张国庆
中国科学院青藏高原研究所,北京 100101
ZHANG Guoqing
收稿日期: 2017-09-25
修回日期: 2018-01-29
网络出版日期: 2018-02-28
版权声明: 2018 地理科学进展 《地理科学进展》杂志 版权所有
基金资助:
作者简介:
作者简介：张国庆(1978-),男,陕西武功人,博士,副研究员,主要从事冰冻圈遥感研究,E-mail: guoqing.zhang@itpcas.ac.cn。
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摘要
青藏高原位于中国西南部、亚洲中部,平均海拔高程大于4000 m,面积约300万km2,是“世界屋脊”,与周边地区一起常被称为地球的“第三极”。青藏高原分布着约1200个面积大于1 km2的湖泊,占中国湖泊数量与面积的一半;同时也是黄河、长江、恒河、印度河等大河的源头,被称为“亚洲水塔”。近几十年来,在全球变暖的背景下,青藏高原升温更加突出,其能量与水循环发生了显著变化,气候趋于暖湿化,冰川加速消融,湖面水位上升。湖泊是气候变化的重要指标,青藏高原湖泊分布密集、人为活动影响较小,多源遥感数据的广泛应用,为监测高原湖泊变化提供了难得的契机。本文依托国家自然科学基金青年项目“基于多源遥感的青藏高原内流区湖泊水量变化及水体相态转换研究(2000-2009年)”,主要研究进展为：初步查明了西藏高原的湖泊数量、面积及水位变化与时空格局,以及湖泊水量变化与水量平衡;探讨了湖泊变化对气候变化的响应。目前对青藏高原湖泊的变化及驱动因素虽有一些认识,但其定量的水量平衡及驱动机制还有待于进一步研究。这对了解世界第三极、一带一路国家和地区水资源状况与变化、生态文明和生态安全屏障建设具有重要的意义,同时也可为第三极国家公园的建立提供重要的科学基础。
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Abstract
The Tibetan Plateau (TP) is located in the southwest of China and central Asia, with a mean elevation higher than 4000 m and area of 3×106 km2. It is named "the roof of the world". The TP and surrounding areas together is also called "the Third Pole". The TP has 1200 lakes greater than 1 km2 in area, which accounts for approximately 50% of the total number and area of lakes in China. It is the sources of the Yellow River, the Yangtze River, the Indus, Ganges, Brahmaputra, Irrawaddy, Salween, and the Mekong, and therefor known as "Asia's water tower". In the past several decades, the TP experienced a faster warming than other regions in the world. The climate of the TP is also getting wetting. Lakes are indicators of climate change. The TP has the dense distribution of lakes with little disturbance of human activities. The utilization of multi-sensors’ data has provided a useful tool to monitor lake change in the remote TP. Several studies of lake changes have been conducted focusing on the following scientific questions: (1) how many lakes are on the TP and what are the spatial and temporal changes of the number, area, and abundance of these lakes? (2) the increased mass over the TP from glaciers or lakes? (3) under anthropogenic warming, how did the water and cryosphere cycles change on the two adjacent largest Plateaus in the world, the Tibetan and the Mongolian Plateaus, over the last four decades? and (4) how did the lake water storage and water balance change? These studies are of great significance to the understanding of the third pole of the world, the state of regional water resources and changes, and ecological civilization and ecological security construction. They also provide an important scientific basis for the planning of the third polar national park. The quantitative understanding of lake water balance and mechanisms and driving factors of lake change needs further work in the future.
Keywords：
青藏高原及周边地区(包括帕米尔高原,兴都库什,喀喇昆仑和喜马拉雅山脉)覆盖有冰川46000多条,总面积约100000 km2,是除南极、北极和格陵兰以外冰川分布最广泛的地区,因此常常将其称为第三极(Qiu, 2008; Yao et al, 2012)。这些冰川是黄河、长江、恒河、印度河等大河的源头,为中国西部及周边地区约20亿人口提供了重要的水源,因此也被称为亚洲水塔(Barnett et al, 2005; Immerzeel et al, 2010; Pritchard, 2017)。近50多年来,青藏高原升温迅速(0.04 oC/a)(Zhang, Yao et al, 2014a),其升温速率是全球温度变化速度的3倍(IPCC, 2014)。在快速变暖的背景下,第三极地区冰冻圈不仅对区域水资源与广泛分布的湖泊变化产生了重要的影响,也对区域气候变化及水循环加强产生了重要的作用,导致第三极地区湖泊变化模式与世界其他地区不同、甚至相反(Pekel et al, 2016; Zhang, Yao, Piao et al, 2017)。
青藏高原是地球系统五大圈层(冰冻圈、大气圈、水圈、生物圈、岩石圈)最集中的地区,湖泊是地球表层系统冰冻圈、大气圈、水圈、生物圈连接的纽带,其变化可为定量评估区域水循环提供钥匙。青藏高原分布着1200多个面积大于1 km2的湖泊,占中国湖泊总数量与面积的一半(Ma et al, 2011)。青藏高原湖泊很少受到人类活动的影响,为研究气候变化提供了重要的指标,是气候变化的前哨。近几年来,很多学者对青藏高原湖泊变化进行了研究,特别是基于遥感监测的青藏高原湖泊变化,内容主要集中在：①面积较大的湖泊(>10 km2)或者时间尺度跨度较大的湖泊面积变化(Ma et al, 2010; Song et al, 2013);②湖泊水位变化研究(Crétaux et al, 2011; Zhang, Xie, Duan et al, 2011; Zhang, Xie, Kang et al, 2011; Kleinherenbrink et al, 2015; Jiang et al, 2017);③少数湖泊的水量平衡定量研究,如纳木错(Zhu et al, 2010; Wu Y H et al, 2014; Li B Q et al, 2017; Li G et al, 2017)、色林错(Zhou et al, 2015; Tong et al, 2016)、青海湖(Zhang et al, 2014b)和当惹雍错、玛旁雍错、佩枯错(Biskop et al, 2016 )等。
青藏高原内流区为一封闭的盆地,湖泊数量与面积占整个高原湖泊的70%左右,湖泊水量变化对其质量变化起主导作用。Gravity Recovery and Climate Experiment(GRACE)地球重力卫星数据估算的总水储量,包括地表水和地下水,其中地表水包括湖泊、冰川、积雪、土壤和冻土水分变化等。为真实地揭示内流区质量变化信息,需对这些不同相态水体水量平衡进行定量评估。Jacob等(2012)利用地球重力卫星数据,发现青藏高原中部及祁连山地区2003-2010年的质量平衡为7±7 Gt/a,认为该地区的冰川在前进。然而,此研究未从GRACE数据反演的总水储量变化中分离出湖泊水量变化(Jacob et al, 2012)。同时,青藏高原中部地区2005-2009年3个冰川实测的物质平衡变化为-549~ -312 mm/a (Yao et al, 2012),遥感监测也发现部分冰川面积与长度呈现出退缩趋势(Yao et al, 2007; Bolch et al, 2010; Yao et al, 2012)。基于“青藏高原内流区质量增加是归因于冰量增加还是湖泊水量增加”这一科学问题,在国家自然科学基金青年科学基金项目“基于多源遥感的青藏高原内流区湖泊水量变化及水体相态转换研究(2000-2009年)(项目批准号：41301063)的资助下,开展了一系列的青藏高原湖泊变化方面的研究,研究内容包括：①湖泊数量、面积及水位变化与时空格局;②湖泊水量变化与水量平衡;③湖泊变化对气候变化的响应。
上述内容涵盖了目前青藏高原湖泊变化遥感监测研究的各个方面,在对这些研究进展归纳总结的基础上,目前仍面临许多尚未解决的科学问题,如：青藏高原湖泊水储量及其空间差异;整个青藏高原单个湖泊水量平衡定量评估;青藏高原湖泊变化的驱动机制。要回答这些问题,需结合多源遥感数据、地面观测、模型模拟等进行协同研究。而这些研究,对了解气候快速变暖背景下,亚洲水塔的水资源与水安全状况、未来变化及其影响都有具十分重要的科学与现实意义。
使用的数据包括遥感数据与气象数据,其中：①遥感数据有湖泊面积提取的Landsat系列卫星遥感影像;湖泊水面高程提取及水位变化研究的ICESat(the Ice, Cloud, and land Elevation Satellite)测高数据;湖泊水量变化研究的多源遥感数据,如GRACE重力卫星数据,雪深测量的被动微波遥感数据等。②实测数据主要为气象站点数据和湖泊水位高程数据。青藏高原自1950年代以来已建立气象站点95个(其中49个自1957年开始),这些气象站点已提供了长期连续的气温、降水、风速、气压、蒸发量等观测数据。气象站点数据为研究基于遥感监测的湖水物理性质和分析湖泊变化的驱动因素提供了必不可少的数据。湖泊水位高程数据主要来自青海湖(1959年至今),为验证遥感水面高程反演提供了必要的验证数据。
美国国家航空和航天局(NASA) Landsat计划,自1972年以来开展了最长且连续的地球卫星观测,包括Landsat MSS(Multispectral Scanner System)(1972-1992)、TM(Thematic Mapper)(1982-)、ETM+(Enhanced Thematic Mapper)(1999-)和Landsat-8 OLI (Operational Land Imager)(2013-)。随着Landsat及其他更多中-高分辨率遥感数据(如高分、中巴、MODIS、哨兵等)的免费公开,发展自动或半自动的湖泊水体信息提取成为必然。目前基于卫星数据的水体分类方法主要有4类,即：专题分类法、线性混合模型、单波段阈值法和光谱水体指数法(Ji et al, 2009)。归一化差异水体指数法(NDWI)是用来区分水体与非水体信息应用最广泛的方法(McFeeters, 1996; Xu, 2006)。一些研究指出,默认的0值作为阈值,可快速地区分水体与非水体 (McFeeters, 1996; Xu, 2006);同时Xu(2006)指出手动调整阈值可以提高水体分类的精度。优化阈值的选取是准确和快速水体分类与湖泊制图的关键。
以Landsat数据为基础,首先将影像的灰度值(DN)转化成表观反射率(TOA),然后结合已有的算法和DEM数据排除云和山体阴影的干扰(Zhu et al, 2015; Li, Shen et al, 2017b)。利用全局—局部的水体半自动提取方法(骆剑承等, 2009; Li et al, 2012; Zhang, Zhang et al, 2017),通过Otsu算法(Otsu, 1979)自动为每一个水体单元选取最优的阈值,可快速地提取出水体信息。在此基础上,结合水库与大坝数据库、河流数据集、在线地图等排除非湖泊水体。对照原始影像对湖泊边界进行人工目视检查与编辑,可快速、准确地完成湖泊制图。目前很多学者也提出了其他水体指数,如改进的归一化差异水体指数(MNDWI)(Xu, 2006)、AWEI(Feyisa et al, 2014)等,在青藏高原湖泊水体信息提取中都表现了较好的效果(Zhang, Li et al, 2017)。湖泊边界的提取,也可完全通过目视解译完成,但不同工作人员判别标准差异、大量的手工操作都会不同程度地引入误差,造成质量下降。实践表明：对青藏高原密集分布湖泊的提取,半自动水体分类结合人工目视检查与编辑是最优方法。
通过分析湖泊稳定状态,确定10月份的数据为最优选择(Zhang, Li et al, 2017)。如果10月无可利用数据,可将数据扩展到9月和11月。通过3年数据窗口可减少季节变化带来的不确定性,同时适用于长时间序列湖泊变化研究。
青藏高原目前只有青海湖、纳木错和羊卓雍错有长期连续的水位观测,这相对于青藏高原1200多个湖泊非常有限(Zhang, Yao et al, 2014b)。稀少的水位观测数据大大限制了对青藏高原湖泊变化及水文过程的理解。ICESat卫星为NASA地球观测系统的一部分,于2003年1月发射,2010年8月停止飞行。ICESat地面采样点的直径为~70 m,采样点之间的距离间隔为172 m(Zwally et al, 2002)。ICESat/ GLA14产品可提供陆地表面高程、大地水准面、波形饱和度及许多其他参数。在平坦的地面上,其绝对精度可达10~15 cm(Zwally et al, 2002)。ICESat激光测高主要用于监测格陵兰岛和南极的冰盖厚度变化,在陆地湖泊与河流的水位高程变化研究中也表现较好(Urban et al, 2008; Zhang, Xie, Duan et al, 2011; Zhang, Xie, Kang et al, 2011)。通过美国国家冰雪中心获取了ICESat/GLA14数据,采用NSIDC提供的IDL程序代码提取出高程及相关信息。利用Landsat数据获取的湖泊边界,选取在湖面上的采样点,去除异常值,从而确保数据不受云及其他环境因素的影响。然后对每次经过的采样点取平均,即为湖面对应时间的水位高程(Zhang, Xie, Kang et al, 2011)。ICESat数据可用时间段为2003-2009年,选取有4~7年数据的湖泊,通过线性回归方法估算湖泊水位变化率。
对面积不规则的湖泊,其体积近似按圆台的体积计算,如公式(1)所示：
式中：S', S为圆台上下底面积,H为圆台高度,湖泊体积变化由两个圆台体积之差求得,即公式(2)：
式中：
湖泊水量平衡可通过水文模型估算,但由于青藏高原气象与水文要素观测数据少,只有少数几个湖泊有定量评估。青藏高原湖泊水量平衡要素包括冰川、雪水当量、冻土层融化、陆面径流和湖面降水与蒸发变化。定量的水量平衡评估需对每一项准确估算。目前青藏高原只有15条冰川有连续的物质平衡观测(Yao et al, 2012),ICESat 数据已被用于估算喜马拉雅地区和青藏高原内流区大尺度范围的冰川厚度变化(Kääb et al, 2012; Gardner et al, 2013; Neckel et al, 2014)。青藏高原湖泊主要分布在内流区,其2003-2009年冰川厚度变化率为1.0±0.5 Gt/a (Gardner et al, 2013; Neckel et al, 2014)。被动微波遥感能穿透云层且对雪层含水量高度敏感,是用来探测积雪厚度最有效的方法。自1978年以来,多个被动微波遥感数据,如scanning multichannel microwave radiometer(SMMR),Special Sensor Microwave/Imager (SSM/I),Special Sensor Microwave Imager/Sounder (SSMI/S),和Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) 被用于估算雪水当量。有学者通过结合气象站点雪深观测数据,发展了长时间序列中国雪深数据集(Che et al, 2008; Dai et al, 2015),可用来估算青藏高原雪水当量变化。季节冻土广泛分布于青藏高原,特别是内流区,近年来冻土退化明显 (Wu Q B et al, 2014; Luo et al, 2016)。目前青藏高原长期连续的冻土活动层厚度变化观测主要分布在青藏高原铁路沿线,已有研究通过模型模拟,如Nelson法(Nelson et al, 2004)、Stefan法 (Stendel et al, 2002)、Kudryavtsev法 (Pang et al, 2009),将其扩展到整个青藏高原(Oelke et al, 2007)。青藏高原气象站点主要分布在东部地区,中西部站点非常匮乏,并且主要分布在海拔较低(< 4800 m)和山谷地带。不同海拔梯度降水存在较大差异,高山地区卫星降水数据,如Tropical Rainfall Measuring Mission (TRMM) 存在较大的误判(Behrangi et al, 2017),大大限制了区域尺度的湖泊水量平衡评估。
GRACE卫星自2002发射以来,被用来估算大尺度的水储量变化,效果较好(Chen et al, 2016; Yi et al, 2016; Asoka et al, 2017)。青藏高原内流区为一封闭的盆地且湖泊主要分布在此流域,此流域作为一个整体,其湖泊水量平衡可用公式(3)表示(Zhang, Yao, Shum et al, 2017)。湖泊水量变化可通过面积与水位变化获得,进而推导出降水变化对湖泊水量变化的贡献。
搭载在Terra和Aqua卫星上的MODIS传感器,分别于1999年12月和2002年5月发射。Terra卫星以下行方式在10: 30 am经过赤道、Aqua卫星以上行方式在1: 30 pm经过赤道(Savtchenko et al, 2004)。这两颗卫星轨道与太阳同步、沿近极地圆轨航行。MODIS有36个不连续、细小的波谱波段(0.4~14.0 μm)对地球表面和云成像,数据产品的空间分辨率有250、500 和1000 m。MODIS LST反演使用分裂窗算法,生成时间分辨率为每日、8天和每月7种产品(Wan et al, 1996)。同时,已有研究表明,夜间地温产品特别是MODIS/Terra卫星数据,相对于白天产品(MODIS/Aqua)有更好的准确性(Schneider et al, 2009; Zhu et al, 2013)。在青藏高原,每天云覆盖可达45%,使用8天合成产品,可大大减少云的干扰(Yu et al, 2016)。采用8天的MODIS/Terra 夜间温度产品(MOD11A2,500 m空间分辨率)来提取湖水表面温度,湖面上3行×3列像元窗口的平均值作为当天的温度值,同时确保与湖岸边有2个像元(1 km)的距离,以减少陆地温度的影响。
目前这些数据与方法的使用仍存在以下一些局限和不确定性：①湖泊面积的提取在方法上主要有目视解译法和水体指数法。人工目视解译法虽对数据质量能得到较好的控制,但由于人工处理工作量大时,会由于操作者的细心与耐心程度而影响湖泊矢量化边界的质量。同时,如果是多人合作完成,不同人对湖泊边界的判别标准(如湿地、沼泽等的区分)差异,也会带来数据质量的不确定性。另外,湖泊通常与河流相连,在裁剪时也需统一,避免因人为因素带来较大的误差。因此,在矢量化前,需制定统一标准,数据完成后,还需交叉检查与核对。②目前青藏高原较大范围的湖泊水位变化研究,主要使用ICESat, CryoSat, 和SRTM这3种数据,特别是ICESat和CryoSat 能提供较高的高程精度,但只有100多个湖泊有可利用的测高数据。同时ICESat(2003-2009)和CryoSat(2010-)可监测的时间段有限。这两种数据联合使用监测2003年以来湖泊水位变化时,由于基准面的不同,会给时间序列变化分析带来一定的不确定性。③通过湖泊面积与水位变化可估算湖泊水量变化。目前湖泊水量变化研究仍局限于有水位高程数据的湖泊,这部分仍占湖泊总数量的一部分,其余湖泊的水量变化通过估算完成,因此整个高原湖泊水量变化估算仍有一定的不确定性。湖泊水量平衡虽可通过多源遥感数据结合或水文模型,对整个流域(盆地)或单个湖泊各贡献因子进行定量评估,但由于水文与气象站点较少或时间尺度较短(如冰川融水径流、降水与蒸发、冻土退化、地下水变化等),其结果的验证仍有一定的局限性。
采用Landsat卫星数据,对青藏高原1970s、1990、2000和2010年大于1 km2的湖泊数量与面积变化进行了详细的研究(Zhang, Yao et al, 2014b)。利用2000年的Landsat 数据,共发现青藏高原有湖泊32842个,总面积为43151.08 km2,占整个青藏高原面积的1.4%,其中大于1 km2的湖泊有1204个。2010年青藏高原面积大于1 km2的湖泊有1236个,主要分布在内流区(面积占整个青藏高原湖泊面积的66%)。在1970s和1990年间,大于1 km2的湖泊总数量和面积都略有减少,然而在1990和2010年间明显增加。近40年来湖泊面积增加了7240 km2(18%),湖泊面积的增加主要发生在2000-2010年间(占40年来的84%)及内流区。湖泊丰度分布统计显示,青藏高原湖泊背离指数分布规律,以面积较大湖泊为主。通过对青藏高原湖泊的详细调查,以及大小分布的评估,对青藏高原湖泊面积及水量变化估算、水资源管理、湖泊-冰川相互作用研究等都具有重要的科学意义。
青藏高原仅有3个湖泊有长期连续的水位观测,分别为青海湖(1959-),羊卓雍错(1974-)和纳木错(2005-)。这些水位观测数据在验证遥感测高数据获取的湖泊水位高程及变化方面发挥重要作用,特别是青海湖。青海湖的水位观测基准面为黄海面,在使用时需要将其转化成WGS84基准面,以便与ICESat或CryoSat高程数据对比(Zhang, Xie, Kang et al, 2011)。利用青海湖实测水位数据对ICESat获取的水位高程数据进行了验证,其相关性较高(r2=0.90),绝对平均误差及均方根误差分别为0.06 m和0.08 m(Zhang, Xie, Kang, et al, 2011),显示ICESat数据在青藏高原湖泊水面高程反演方面具有较高的精度。
利用ICESat数据对青藏高原湖泊水位变化进行监测,111个湖泊有可利用的ICESat数据,其中74个湖泊有4年以上的数据,2003-2009年间湖水位平均变化率为0.21 m/a(Zhang, Xie, Duan et al, 2011a)。湖面增加的湖泊的平均变化率为0.26 m/a (0.01~0.80 m/a),湖面降低的湖泊的平均变化率为-0.06 m/a (-0.40~-0.02 m/a)。湖面增加的盐湖的平均变化率为0.27 m/a,湖面降低的盐湖的平均变化率为-0.10 m/a(-0.40~-0.03 m/a)。湖面增加的淡水湖的平均变化率为0.24 m/a(0.01~0.39 m/a),湖面降低的淡水湖的平均变化率为-0.03 m/a (-0.04~ -0.02 m/a) 。同时也通过利用ICESat与SRTM DEM两种高程数据的高程差,对青藏高原2000-2009年湖泊水位变化进行研究。
通过结合湖泊水位变化与面积,对青藏高原2000-2009年湖泊水量变化进行估算(Zhang, Yao, et al, 2013)。200个有ICESat数据湖泊的平均湖面和水量变化率分别为0.14 m/a和4.95 Gt/a。内流区的118个湖泊,平均湖面高程变化率为0.20 m/a、水量变化率为4.28 Gt/a,占青藏高原有ICESat湖泊数量(200)的59%、水量的86%。根据其面积比例对青藏高原内流区和整个青藏高原所有湖泊的水量进行了估算,其水量变化率分别为8.06和8.76 Gt/a,这与GRACE反演的青藏高原内流区质量平衡~7 Gt/a相当(Jacob et al, 2012)。此研究揭示了GRACE反演的质量平衡增加,主要应归因于湖泊水量的增加,而不是冰川物质正平衡。
青藏高原湖泊主要分布在内流区,而内流区只有4个长期观测的气象站点,同时全球格点气候数据或再分析资料在青藏高原具有较大的不确定性,大大制约了湖泊水量平衡的定量评估。青藏高原湖泊变化原因,以往的研究主要以定性分析为主。Lei等(2012)通过对令戈错水量与流域冰川物质平衡估算,认为冰川融水对其扩张占主体。Li等(2014)通过对湖泊面积和水位变化分析,结合空间变化模式和降水变化,推测冻土退化可能是湖泊变化的主要驱动因素。另外,也有研究通过对比湖泊水位(面积)与降水变化,发现二者在趋势与空间上匹配较好,从而推测降水贡献占主体(Lei et al, 2014; Song et al, 2014; Zhang, Yao, Piao, et al, 2017)。也有研究利用水文模型对色林错(Zhou et al, 2015; Tong et al, 2016)和纳木错(Li G et al, 2017; Li B Q et al, 2017)水量平衡进行了定量评估,认为冰川融水占这两个西藏最大湖泊的水量增加的10%左右。显然,这些研究对青藏高原广泛分布的湖泊水量平衡的解析还非常有限。
多源遥感数据的使用为内流区湖泊水量变化及水量平衡整体评估提供新思路。利用湖泊面积与水位的高相关性(Zhang, Xie, et al, 2013),通过湖泊面积估算湖面水位,对青藏高原1970s-2015年每年湖泊面积、水位、水量变化进行研究。结果表明：青藏高原湖泊面积、水位与水量变化相似,并同时经历了3个阶段,即：1970s-1995年间略有减少,1996-2010年间快速增加,近几年来(2011-2015年)增速减缓(Zhang, Yao, Shum, et al, 2017)。结合GRACE重力卫星数据、土壤水分、雪水当量、冰川物质平衡、冻土消融、湖泊水量,对2003-2009年青藏高原内流区质量平衡与湖泊水量平衡进行了估算。研究表明：湖泊水量增量(7.72±0.63 Gt/a)与地下水储量(5.01±1.59 Gt/a)相似。降水对湖泊水量增加占主体(74%),其次为冰川消融(13%)与冻土退化(12%),积雪消融贡献较少(1%)(Zhang, Yao, Shum et al, 2017)。由于ICESat数据的限制,目前只对2003-2009年间湖泊水量平衡进行了估算。但随着TanDEM-X以及更多测高数据的利用,如Jason-3、sentinel-3A和3B、ICESat-2、Jason-CS、SWOT等,湖泊水量平衡估算的时间和空间尺度都可被扩展,直接估算湖泊水量平衡成为可能。
(1) 湖水表面温度变化
湖泊是气候变化研究的重要指标之一,受气候相关的多方面因素影响,如湖冰的冻融(Kropáček et al, 2013)、积雪动态(Zhang et al, 2012; Zhang, Xie, et al, 2014b; Yu et al, 2016)、径流、湖泊水位与水量变化(Zhang, Yao et al, 2013, 2014a; Zhang, Yao, Shum et al, 2017)。湖水表面温度变化是对气候变化的重要响应(Zhang, Yao et al, 2014a; O'Reilly et al, 2015)。特别是在青藏高原地区,人为影响因素少,冰川、积雪广泛分布,海拔高、梯度差异大,是利用湖水温度这一自然环境指标开展湖泊对气候变化响应研究的理想地区。然而,青藏高原只有青海湖有长期的湖水温度监测数据。基于站点观测资料验证表明,Moderate Resolution Imaging Spectroradiometer (MODIS) 陆表温度绝对辐射精度可达1 K(Wan, Zhang, Li et al, 2002; Wan, Zhang, Zhang et al, 2002; Coll et al, 2005)。另外,监测湖水表面温度方面,MODIS 陆表温度数据(LST)也表现较好(Reinart et al, 2008; Crosman et al, 2009; Schneider et al, 2009),为利用遥感数据,在地球观测系统(EOS)记录的时间尺度上监测整个青藏高原湖水温度变化提供了可能。
利用MODIS LST产品(MOD11A2),研究52个有可利用MODIS温度产品覆盖湖泊的湖水表面温度变化,发现平均的湖水温度变化率为0.012 oC/a,升温湖泊湖面平均变化率为0.055 oC/a,降温湖泊湖面平均变化率为-0.053 oC/a(Zhang, Yao, et al, 2014a)。17个有可利用附近气象站点数据的湖泊,其中9个湖泊升温率比气象站点气温和陆温升高更快。另外,对气象站点气温、陆温和湖水表面温度变化随海拔梯度变化特征进行了分析。总体来看,湖水升温和降温(加快的冰川融化冷水补给)都是由于气候变暖引起。
(2) 青藏高原与蒙古高原湖泊变化对比
区域尺度的湖泊对比研究对了解不同区域对气候变化的响应非常重要。不同区域的高山湖泊对气候变化的响应主要依赖于其受大尺度大气环流、区域气候、及冰冻圈过程的影响。除地球南北极外,青藏高原和蒙古高原也是气候变化最敏感的地区。与邻近的蒙古高原不同,青藏高原有广泛分布的冰川。过去几十年来,这两个高原经历了相似的快速变暖,升温率是地球其他地区的3倍。考虑到更为强烈的环境变化及西风、季风系统和其他气候现象的影响,两个高原的水循环可能发生显著的变化。
利用遥感数据对过去40多年来(1970s-2013年)两个高原的湖泊变化进行了监测与对比研究。结果表明：青藏高原湖泊变化特征体现为湖泊的扩张和新湖泊的出现;长期连续时间序列湖泊(内流区)的快速扩张,主要发生在1997/1998年后;在空间上,青藏高原南部(雅鲁藏布江流域)湖泊出现萎缩,但其变化幅度较小,其他流域湖泊则无明显的变化趋势。蒙古高原湖泊出现消失和萎缩,连续时间序列变化显示其萎缩主要发生在1997/1998年后。湖泊水量平衡变化分析显示,青藏高原湖泊的扩张主要归因于降水的增加和冰冻圈的贡献,在内流区尤为突出。而蒙古高原湖泊的萎缩主要归因于降水的减少,同时伴随有人类活动的影响,其中内蒙古比外蒙古更为明显(Tao et al, 2015)。上述两个高原湖泊变化相反的模式及水循环的变化,特别是时间序列拐点发生在1997/1998年,可认为是大尺度及区域大气环流变化对气候变暖的响应(Zhang, Yao, Piao et al, 2017)。
青藏高原暖—湿的气候和蒙古高原暖—干的气候,是导致过去40多年来两个高原湖泊变化呈现完全不同模式的主要原因。此研究为区域水资源和生态系统管理提供了重要信息,为在区域尺度上制定适当的适应和管理战略提供决策支持。
在全球变暖、青藏高原气候暖—湿背景下,冰川消融加速、冻土退化,综合促使青藏高原湖泊的快速变化。目前青藏高原湖泊面积、水位与水量变化,以及湖泊变化对气候的响应虽有诸多报道,然而仍面临许多挑战,如湖泊总水储量估算、湖泊变化原因解释、驱动机制、能量平衡、局地环流、以及与冻土层/地下水等的关系、未来变化预测方面的研究还比较欠缺。现将目前面临的挑战总结如下：
(1) 湖泊总水储量估算及其空间特征
青藏高原面积大于10 km2的湖泊有424个,大于50 km2的湖泊有169个,这些大湖总水储量的轻微变化可能诱发地震,引起周边地区水资源及生态系统的变化。目前青藏高原有近40个湖泊有水深测量,然而相对于整个青藏高原湖泊数量(1200个)与分布,目前对第三极地区湖泊总储水量的理解仍非常有限,迫切需要结合更多的测量数据与地学统计模型对其进行全面的估算,以加强对亚洲水塔湖泊总储水量的定量认识。
(2) 湖泊水量平衡定量评估
由于青藏高原气象与水文观测站点的稀少,特别是湖泊集中分布的内流区,大大制约了湖泊水量平衡的定量估算。青藏高原湖泊整体水量的增加,冰川消融占主体还是降水增加占主体,目前仍有较大争议。这些争议的解决,依赖于整个青藏高原更多湖泊水量平衡的定量评估。目前则可通过TanDEM-X、ASTER、CryoSat-2等数据监测冰川厚度(冰储量)变化,InSAR技术监测冻土活动层厚度变化,模型模拟陆面与湖面蒸发变化等手段,不断量化冰川与冻土消融及降水—蒸发变化对湖泊水量变化的影响。随着更多遥感卫星的发射及数据的开放获取,及更多气象与水文站点的建设和数据共享,不断地推进湖泊水量平衡定量研究。
(3) 湖泊变化的驱动机制
通过对青藏高原湖泊的遥感及野外调查,研究过去40多年来湖泊年际变化趋势和年代际动态变化过程、空间和不同类型湖泊(冰川补给和非冰川补给)变化差异。选择典型湖泊对影响湖泊变化的重要指标进行长期连续观测,结合驱动数据和水文模型,综合定量评估降水、冰川融水、冻土活动层和积雪融水变化对湖泊水量变化的贡献。同时分析区域及大尺度大气环流对湖泊水量变化的影响,厘清亚洲“水塔”在气候快速变化背景下,湖泊不同演化阶段的驱动机制。虽然湖泊水量变化的空间差异非常明确,但相应的气候变化机制并不清楚。未来研究需进一步探索气候变化影响降水的空间格局,特别应关注年代际甚至多年代际气候变率对水汽传输的影响。
The authors have declared that no competing interests exist.
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分步迭代的多光谱遥感水体信息高精度自动提取 [J].https://doi.org/10.11834/jrs.20090405 Magsci [本文引用: 1] 摘要
以LANDSAT卫星遥感数据为信息源, 在归一化差异水指数(NDWI)计算的基础上, 采用“全域―局部”的分步迭代空间尺度转换机制, 将全域分割、全域分类、局部分割与分类等计算过程有机地结合起来, 分阶段地融合了水体信息提取所需的不同层次知识, 并建立迭代算法实现了水体最佳边缘的逐步逼近, 获得了高精度的水体信息提取。通过对青藏高原试验区湖泊信息提取的实验表明, 该方法除了能够实现对复杂多样的水体信息进行高精度自动提取外, 还可有效避免与阴影等信息的混淆。
Automatic and high-precise extraction for water information from multispectral images with the step-by-step iterative transformation mechanism [J].https://doi.org/10.11834/jrs.20090405 Magsci [本文引用: 1] 摘要
以LANDSAT卫星遥感数据为信息源, 在归一化差异水指数(NDWI)计算的基础上, 采用“全域―局部”的分步迭代空间尺度转换机制, 将全域分割、全域分类、局部分割与分类等计算过程有机地结合起来, 分阶段地融合了水体信息提取所需的不同层次知识, 并建立迭代算法实现了水体最佳边缘的逐步逼近, 获得了高精度的水体信息提取。通过对青藏高原试验区湖泊信息提取的实验表明, 该方法除了能够实现对复杂多样的水体信息进行高精度自动提取外, 还可有效避免与阴影等信息的混淆。
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Relative contribution of monsoon precipitation and pumping to changes in groundwater storage in India [J].https://doi.org/10.1038/ngeo2869 URL [本文引用: 1] 摘要
The depletion of groundwater resources threatens food and water security in India. However, the relative influence of groundwater pumping and climate variability on groundwater availability and storage remains unclear. Here we show from analyses of satellite and local well data spanning the past decade that long-term changes in monsoon precipitation are driving groundwater storage variability in most parts of India either directly by changing recharge or indirectly by changing abstraction. We find that groundwater storage has declined in northern India at the rate of 2 cm yrand increased by 1 to 2 cm yrin southern India between 2002 and 2013. We find that a large fraction of the total variability in groundwater storage in north-central and southern India can be explained by changes in precipitation. Groundwater storage variability in northwestern India can be explained predominantly by variability in abstraction for irrigation, which is in turn influenced by changes in precipitation. Declining precipitation in northern India is linked to Indian Ocean warming, suggesting a previously unrecognized teleconnection between ocean temperatures and groundwater storage.
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| [3] |
Potential impacts of a warming climate on water availability in snow-dominated regions [J].https://doi.org/10.1038/nature04141 URL [本文引用: 1] |
| [4] |
Using GRACE to constrain precipitation amount over cold mountainous basins [J].https://doi.org/10.1002/2016GL071832 URL [本文引用: 1] 摘要
Despite the importance for hydrology and climate-change studies, current quantitative knowledge on the amount and distribution of precipitation in mountainous and high-elevation regions is limited due to instrumental and retrieval shortcomings. Here by focusing on two large endorheic basins in High Mountain Asia, we show that satellite gravimetry (Gravity Recovery and Climate Experiment (GRACE)) can be used to provide an independent estimate of monthly accumulated precipitation using mass balance equation. Results showed that the GRACE-based precipitation estimate has the highest agreement with most of the commonly used precipitation products in summer, but it deviates from them in cold months, when the other products are expected to have larger errors. It was found that most of the products capture about or less than 50% of the total precipitation estimated using GRACE in winter. Overall, Global Precipitation Climatology Project (GPCP) showed better agreement with GRACE estimate than other products. Yet on average GRACE showed 30% more annual precipitation than GPCP in the study basins. In basins of appropriate size with an absence of dense ground measurements, as is a typical case in cold mountainous regions, we find GRACE can be a viable alternative to constrain monthly and seasonal precipitation estimates from other remotely sensed precipitation products that show large bias.
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| [5] |
Differences in the water-balance components of four lakes in the southern-central Tibetan Plateau [J].https://doi.org/10.5194/hess-20-209-2016 URL [本文引用: 1] 摘要
The contrasting patterns of lake-level fluctuations across the Tibetan Plateau (TP) are indicators of differences in the water balance over the TP. However, little is known about the key hydrological factors controlling this variability. The purpose of this study is to contribute to a more quantitative understanding of these factors for four selected lakes in the southern-central part of the TP: Nam Co and Tangra Yumco (increasing water levels), and Mapam Yumco and Paiku Co (stable or slightly decreasing water levels). We present the results of an integrated approach combining hydrological modeling, atmospheric-model output and remote-sensing data. The J2000g hydrological model was adapted and extended according to the specific characteristics of closed-lake basins on the TP and driven with High Asia Refined analysis (HAR) data at 10 m resolution for the period 2001 2010. Differences in the mean annual water balances among the four basins are primarily related to higher precipitation totals and attributed runoff generation in the Nam Co and Tangra Yumco basins. Precipitation and associated runoff are the main driving forces for inter-annual lake variations. The glacier-meltwater contribution to the total basin runoff volume (between 14 and 30 % averaged over the 10-year period) plays a less important role compared to runoff generation from rainfall and snowmelt in non-glacierized land areas. Nevertheless, using a hypothetical ice-free scenario in the hydrological model, we indicate that ice-melt water constitutes an important water-supply component for Mapam Yumco and Paiku Co, in order to maintain a state close to equilibrium, whereas the water balance in the Nam Co and Tangra Yumco basins remains positive under ice-free conditions. These results highlight the benefits of linking hydrological modeling with atmospheric-model output and satellite-derived data, and the presented approach can be readily transferred to other data-scarce closed lake basins, opening new directions of research. Future work should go towards a better assessment of the model-chain uncertainties, especially in this region where observation data are scarce.
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| [6] |
A glacier inventory for the western Nyainqentanglha Range and the Nam Co Basin, Tibet, and glacier changes 1976-2009 [J].https://doi.org/10.5194/tc-4-419-2010 URL [本文引用: 1] 摘要
The western Nyainqentanglha range is located in the south-eastern centre of the Tibetan Plateau. Its western slope drains into Lake Nam Co. The area is of special interest for glacio-climatological research as this region is influenced by both the continental climate of central Asia and the Indian Monsoon system and it is situated at the transition zone between temperate and subcontinental glaciers. A glacier inventory for the whole mountain range for the year ~2000 was generated using automated remote sensing and GIS techniques based on Landsat ETM+ and SRTM3 DEM data. Change analysis is based on data from Hexagon KH-9 and Landsat MSS (year 1976), Metric Camera (year 1984), and Landsat TM/ETM+ (1991, 2001, 2005, 2009). Manual adjustment was especially necessary for the panchromatic Hexagon data and for debris covered glaciers. The whole mountain range contains about 960 glaciers covering an area of 795.6 卤 22.3 km虏 while the catchment area of Nam Co covers 198.1 卤 5.6 km虏. The median elevation of the glaciers is ~5800 m a.s.l. with the majority terminating around 5600 m. Five glaciers with debris-covered tongues terminate lower than 5200 m. The glacier area decreased between 1976 and 2001 by about 6 卤 3%, which is less than presented in previous studies based on topographic maps from the 1970s and Landsat data from 2000. The shrinkage rate increased in the period 2001 - 2009. No advancing glaciers were detected. Detailed length measurements for five glaciers indicate a retreat of the tongues of around 10 m per year (1976-2009) with higher absolute but lower relative values for the larger glaciers. No consistent trend was found for the rate of change within the investigation period which might indicate different response times of individual glaciers.
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| [7] |
Snow depth derived from passive microwave remote-sensing data in China [J].https://doi.org/10.3189/172756408787814690 URL [本文引用: 1] 摘要
In this study, we report on the spatial and temporal distribution of seasonal snow depth derived from passive microwave satellite remote-sensing data (e.g. SMMR from 1978 to 1987 and SMM/I from 1987 to 2006) in China. We first modified the Chang algorithm and then validated it using meteorological observation data, considering the influences from vegetation, wet snow, precipitation, cold desert and frozen ground. Furthermore, the modified algorithm is dynamically adjusted based on the seasonal variation of grain size and snow density. Snow-depth distribution is indirectly validated by MODIS snow-cover products by comparing the snow-extent area from this work. The final snow-depth datasets from 1978 to 2006 show that the interannual snow-depth variation is very significant. The spatial and temporal distribution of snow depth is illustrated and discussed, including the steady snow-cover regions in China and snow-mass trend in these regions. Though the areal extent of seasonal snow cover in the Northern Hemisphere indicates a weak decrease over a long period, there is no clear trend in change of snow-cover area extent in China. However, snow mass over the Qinghai-Tibetan Plateau and northwestern China has increased, while it has weakly decreased in northeastern China. Overall, snow depth in China during the past three decades shows significant interannual variation, with a weak increasing trend.
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| [8] |
Groundwater storage changes: Present status from GRACE observations [J].https://doi.org/10.1007/s10712-015-9332-4 URL [本文引用: 1] 摘要
Satellite gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) provide quantitative measurement of terrestrial water storage (TWS) changes with unprecedented accuracy. Combining GRACE-observed TWS changes and independent estimates of water change in soil and snow and surface reservoirs offers a means for estimating groundwater storage change. Since its launch in March 2002, GRACE time-variable gravity data have been successfully used to quantify long-term groundwater storage changes in different regions over the world, including northwest India, the High Plains Aquifer and the Central Valley in the USA, the North China Plain, Middle East, and southern Murray-Darling Basin in Australia, where groundwater storage has been significantly depleted in recent years (or decades). It is difficult to rely on in situ groundwater measurements for accurate quantification of large, regional-scale groundwater storage changes, especially at long timescales due to inadequate spatial and temporal coverage of in situ data and uncertainties in storage coefficients. The now nearly 13 years of GRACE gravity data provide a successful and unique complementary tool for monitoring and measuring groundwater changes on a global and regional basis. Despite the successful applications of GRACE in studying global groundwater storage change, there are still some major challenges limiting the application and interpretation of GRACE data. In this paper, we present an overview of GRACE applications in groundwater studies and discuss if and how the main challenges to using GRACE data can be addressed.
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| [9] |
Ground measurements for the validation of land surface temperatures derived from AATSR and MODIS data [J].https://doi.org/10.1016/j.rse.2005.05.007 URL [本文引用: 1] 摘要
An experimental site was set up in a large, flat and homogeneous area of rice crops for the validation of satellite derived land surface temperature (LST). Experimental campaigns were held in the summers of 2002–2004, when rice crops show full vegetation cover. LSTs were measured radiometrically along transects covering an area of 1 km 2. A total number of four thermal radiometers were used, which were calibrated and inter-compared through the campaigns. Radiometric temperatures were corrected for emissivity effects using field emissivity and downwelling sky radiance measurements. A database of ground-based LSTs corresponding to morning, cloud-free overpasses of Envisat/Advanced Along-Track Scanning Radiometer (AATSR) and Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) is presented. Ground LSTs ranged from 25 to 32 °C, with uncertainties between ± 0.5 and ± 0.9 °C. The largest part of these uncertainties was due to the spatial variability of surface temperature. The database was used for the validation of LSTs derived from the operational AATSR and MODIS split-window algorithms, which are currently used to generate the LST product in the L2 level data. A quadratic, emissivity dependent split-window equation applicable to both AATSR and MODIS data was checked as well. Although the number of cases analyzed is limited (five concurrences for AATSR and eleven for MODIS), it can be concluded that the split-window algorithms work well, provided that the characteristics of the area are adequately prescribed, either through the classification of the land cover type and the vegetation cover, or with the surface emissivity. In this case, the AATSR LSTs yielded an average error or bias of 61 0.9 °C (ground minus algorithm), with a standard deviation of 0.9 °C. The MODIS LST product agreed well with the ground LSTs, with differences comparable or smaller than the uncertainties of the ground measurements for most of the days (bias of + 0.1 °C and standard deviation of 0.6 °C, for cloud-free cases and viewing angles smaller than 60°). The quadratic split-window algorithm resulted in small average errors (+ 0.3 °C for AATSR and 0.0 °C for MODIS), with differences not exceeding ± 1.0 °C for most of the days (standard deviation of 0.9 °C for AATSR and 0.5 °C for MODIS).
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| [10] |
SOLS: A lake database to monitor in the Near Real Time water level and storage variations from remote sensing data [J].https://doi.org/10.1016/j.asr.2011.01.004 URL [本文引用: 1] 摘要
An accurate and continuous monitoring of lakes and inland seas is available since 1993 thanks to the satellite altimetry missions (Topex–Poseidon, GFO, ERS-2, Jason-1, Jason-2 and Envisat). Global data processing of these satellites provides temporal and spatial time series of lakes surface height with a decimetre precision on the whole Earth. The response of water level to regional hydrology is particularly marked for lakes and inland seas in semi-arid regions. A lake data centre is under development at by LEGOS (Laboratoire d’Etude en Géophysique et Océanographie Spatiale) in Toulouse, in coordination with the HYDROLARE project (Headed by SHI: State Hydrological Institute of the Russian Academy of Science). It already provides level variations for about 150 lakes and reservoirs, freely available on the web site (HYDROWEB: http://www.LEGOS.obs-mip.fr/soa/hydrologie/HYDROWEB ), and surface-volume variations of about 50 big lakes are also calculated through a combination of various satellite images (Modis, Asar, Landsat, Cbers) and radar altimetry. The final objective is to achieve in 2011 a fully operating data centre based on remote sensing technique and controlled by the in situ infrastructure for the Global Terrestrial Network for Lakes (GTN-L) under the supervision of WMO (World Meteorological Organization) and GCOS (Global Climate Observing System).
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| [11] |
MODIS-derived surface temperature of the Great Salt Lake [J].https://doi.org/10.1016/j.rse.2008.08.013 URL [本文引用: 1] 摘要
The dominant SWT signal is the annual cycle (with a range of 26°C and peak temperature in mid-July) while the diurnal range is as large as 4°C during the spring season. Year-to-year variations in SWT are largest during the fall with over 1°C anomalously warm (cold) departures from the 8-year monthly medians observed during fall 2001 (2006). The MODIS imagery provides an updated SWT climatology for operational weather forecasting applications (e.g., lake-effect snow storm prediction) as well as for input into operational and research numerical weather prediction models.
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| [12] |
Inter-calibrating SMMR, SSM/I and SSMI/S data to improve the consistency of snow-depth products in China [J].https://doi.org/10.3390/rs70607212 URL [本文引用: 1] 摘要
Long-term snow depth/snow water equivalent (SWE) products derived from passive microwave remote sensing data are fundamental for climatological and hydrological studies. However, the temporal continuity of the products is affected by the updating or replacement of passive microwave sensors or satellite platforms. In this study, we inter-calibrated brightness temperature (Tb) data obtained from the Special Sensor Microwave Imager (SSM/I) and the Special Sensor Microwave Imager/Sounder (SSMI/S). Then, we evaluated the consistency of the snow cover area (SCA) and snow depth derived from the Scanning Multichannel Microwave Radiometer (SMMR), SSM/I and SSMI/S. The results indicated that (1) the spatial pattern of the SCA derived from the SMMR and SSM/I data was more consistent after calibration than before; (2) the relative biases in the SCA and snow depth in China between the SSM/I and SSMI/S data decreased from 42.42% to 1.65% and from 66.18% to 1.5%, respectively; and (3) the SCA and snow depth derived from the SSM/I data carried on F08, F11 and F13 were highly consistent. To obtain consistent snow depth and SCA products, inter-sensor calibrations between SMMR, SSM/I and SSMI/S are important. In consideration of the snow data product continuation, we suggest that the brightness temperature data from all sensors be calibrated based on SSMI/S.
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| [13] |
Automated Water Extraction Index: A new technique for surface water mapping using Landsat imagery [J].https://doi.org/10.1016/j.rse.2013.08.029 URL [本文引用: 1] 摘要
61We introduced a new automated method that improves surface water mapping accuracy.61The new method improves mapping accuracy by enhancing spectral contrast.61The new method was tested on several water bodies in different parts of the world.61Accuracy of the new method is consistently higher than that of MNDWI and MaxLike.61The new index also has fairly stable optimal threshold for accurate classification.
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| [14] |
A reconciled estimate of glacier contributions to sea level rise: 2003 to 2009 [J].https://doi.org/10.1126/science.1234532 URL PMID: 23687045 [本文引用: 2] 摘要
Abstract Glaciers distinct from the Greenland and Antarctic Ice Sheets are losing large amounts of water to the world's oceans. However, estimates of their contribution to sea level rise disagree. We provide a consensus estimate by standardizing existing, and creating new, mass-budget estimates from satellite gravimetry and altimetry and from local glaciological records. In many regions, local measurements are more negative than satellite-based estimates. All regions lost mass during 2003-2009, with the largest losses from Arctic Canada, Alaska, coastal Greenland, the southern Andes, and high-mountain Asia, but there was little loss from glaciers in Antarctica. Over this period, the global mass budget was -259 00± 28 gigatons per year, equivalent to the combined loss from both ice sheets and accounting for 29 00± 13% of the observed sea level rise.
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| [15] |
Climate change will affect the Asian water towers [J].https://doi.org/10.1126/science.1183188 URL PMID: 20538947 [本文引用: 1] 摘要
More than 1.4 billion people depend on water from the Indus, Ganges, Brahmaputra, Yangtze, and Yellow rivers. Upstream snow and ice reserves of these basins, important in sustaining seasonal water availability, are likely to be affected substantially by climate change, but to what extent is yet unclear. Here, we show that meltwater is extremely important in the Indus basin and important for the Brahmaputra basin, but plays only a modest role for the Ganges, Yangtze, and Yellow rivers. A huge difference also exists between basins in the extent to which climate change is predicted to affect water availability and food security. The Brahmaputra and Indus basins are most susceptible to reductions of flow, threatening the food security of an estimated 60 million people.
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| [16] |
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| [17] |
Recent contributions of glaciers and ice caps to sea level rise [J].https://doi.org/10.1038/nature10847 URL [本文引用: 3] |
| [18] |
Analysis of dynamic thresholds for the normalized difference water index [J].https://doi.org/10.14358/PERS.75.11.1307 URL [本文引用: 1] 摘要
The normalized difference water index (NDWI) has been successfully used to delineate surface water features. However, two major problems have been often encountered: (a) NDWIS calculated from different band combinations [visible, near-infrared, or shortwave-infrared (SWIR)] can generate different results, and (b) NDWI thresholds vary depending on the proportions of subpixel water/non-water components. We need to evaluate all the NDWIS for determining the best performing index and to establish appropriate thresholds for clearly identifying water features. We used the spectral data obtained from a spectral library to simulate the satellite sensors Landsat
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| [19] |
Monitoring recent lake level variations on the Tibetan Plateau using CryoSat-2 SARIn mode data [J].https://doi.org/10.1016/j.jhydrol.2016.11.024 URL [本文引用: 1] 摘要
Lakes on the Tibetan Plateau (TP) are of great interest due to their value as water resources but also as an important indicator of climate change. However, in situ data in this region are extremely scarce and only a few lakes have gauge measurements. Satellite altimetry has been used successfully to monitor lake levels. In this study, Cryosat-2 SARIn mode data over the period 2010 to 2015 are used to investigate recent lake level variations. The estimated water levels of the 70 largest lakes (> 100 km 2 ) on the TP show that 48 lakes reveal a rising trend (avg. 0.28 0.06 m/yr) while the other 22 show a slightly decreasing trend (avg. -0.10 0.04 m/yr). To compare with the change rates during 2003-2009, ICESat data which cover 42 of the 70 lakes are also used. When combining the data, the results show that during the period of 2003-2015, 28 lakes maintained a rising trend and the change rates are comparable. Lakes in the northern part of the TP experienced pronounced rising (avg. 0.37 0.10 m/yr), while lakes in southern part were steady or decreasing even in glaciated basins with high precipitation. Factor analysis indicates that driving factors for lake change are variable due to high spatial heterogeneity. However, autumn/winter temperature plays an important role in lake level change. These results demonstrate that lakes on the TP are still rapidly changing under climate change, especially in northern part of the TP, but the driving factors are variable and more research is needed to understand the mechanisms behind observed changes.
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| [20] |
Contrasting patterns of early twenty-first-century glacier mass change in the Himalayas [J].https://doi.org/10.1038/nature11324 URL PMID: 200101 [本文引用: 1] 摘要
Glaciers are among the best indicators of terrestrial climate variability, contribute importantly to water resources in many mountainous regions and are a major contributor to global sea level rise. In the Hindu Kush-Karakoram-Himalaya region (HKKH), a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance. There is, however, indirect evidence of a complex pattern of glacial responses in reaction to heterogeneous climate change signals. Here we use satellite laser altimetry and a global elevation model to show widespread glacier wastage in the eastern, central and south-western parts of the HKKH during 2003-08. Maximal regional thinning rates were 0.6665±650.09 metres per year in the Jammu-Kashmir region. Conversely, in the Karakoram, glaciers thinned only slightly by a few centimetres per year. Contrary to expectations, regionally averaged thinning rates under debris-mantled ice were similar to those of clean ice despite insulation by debris covers. The 2003-08 specific mass balance for our entire HKKH study region was -0.2165±650.0565m65yr(-1) water equivalent, significantly less negative than the estimated global average for glaciers and ice caps. This difference is mainly an effect of the balanced glacier mass budget in the Karakoram. The HKKH sea level contribution amounts to one per cent of the present-day sea level rise. Our 2003-08 mass budget of -12.865±653.5 gigatonnes (Gt) per year is more negative than recent satellite-gravimetry-based estimates of -565±65365Gt65yr(-1) over 2003-10 (ref. 12). For the mountain catchments of the Indus and Ganges basins, the glacier imbalance contributed about 3.5% and about 2.0%, respectively, to the annual average river discharge, and up to 10% for the Upper Indus basin.
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| [21] |
Monitoring of lake level changes on the Tibetan Plateau and Tian Shan by retracking Cryosat SARIn waveforms [J].https://doi.org/10.1016/j.jhydrol.2014.11.063 URL [本文引用: 1] 摘要
In this study we present, for the first time, the application of Cryosat SARIn mode data to monitor lakes in mountainous areas and to find their water balance. By applying a novel retracker, tailored for lake level observations, we find at least four useable passes for 125 lakes on the Tibetan Plateau and Tian Shan areas over the period February 2012 to January 2014. From these 125 lakes, 30 are passed at least ten times, for which we compute trends and periodic variations, and 16 lakes more then twenty times, for which we additionally apply a water slope correction. This slope correction accounts for geoid inaccuracies or wind effects. We compared the results over two lakes, Langa Co and Bosten, with Jason-2 measurements. Over Langa Co we find an RMS difference of 0.5502m, while for Lake Bosten this is only 0.2602m. For Lake Bosten, the estimated trends, annual and semi-annual variations from the Cryosat and Jason-2 datasets are compared as well. The estimated amplitudes are comparable, while derived phases differ by a few days. Using the trends of all lakes passed at least ten times, a water volume balance of natural lakes is estimated. A loss of 1.5102±020.1102km 3 02y 611 is observed in the lakes in the Tian Shan area. In Tibet, a positive mass balance is estimated of 1.7602±020.2402km 3 02y 611 .
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| [22] |
Analysis of ice phenology of lakes on the Tibetan Plateau from MODIS data [J].https://doi.org/10.5194/tc-7-287-2013 URL [本文引用: 1] 摘要
The Tibetan Plateau includes a large system of endorheic (closed basin) lakes. Lake ice phenology, i.e. the timing of freeze-up and break-up and the duration of the ice cover may provide valuable information about climate variations in this region. The ice phenology of 59 large lakes on the Tibetan Plateau was derived from Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day composite data for the period from 2001 to 2010. Ice cover duration appears to have a high variability in the studied region due to both climatic and local factors. Mean values for the duration of ice cover were calculated for three groups of lakes defined by clustering, resulting in relatively compact geographic regions. In each group several lakes showed anomalies in ice cover duration in the studied period. Possible reasons for such anomalous behaviour are discussed. Furthermore, many lakes do not freeze up completely during some seasons. This was confirmed by inspection of high resolution optical data. Mild winter seasons, large water volume and/or high salinity are the most likely explanations. Trends in the ice cover duration derived by linear regression for all the studied lakes show a high variation in space. A correlation of ice phenology variables with parameters describing climatic and local conditions showed a high thermal dependency of the ice regime. It appears that the freeze-up tends to be more thermally determined than break-up for the studied lakes.
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| [23] |
Response of inland lake dynamics over the Tibetan Plateau to climate change [J].https://doi.org/10.1007/s10584-014-1175-3 URL [本文引用: 1] |
| [24] |
Glacier mass loss induced the rapid growth of Linggo Co on the central Tibetan Plateau [J].https://doi.org/10.3189/2012JoG11J025 URL [本文引用: 1] 摘要
Remote-sensing and GIS techniques in conjunction with field investigations show how glacier mass loss has led to the rapid growth of Linggo Co, a glacier-fed lake on the central Tibetan Plateau, which has expanded by 21.3% in area between 1974 and 2010, with a lake-level rise of 6511.2 m. The lake volume of Linggo Co increased at a rate of 0.02 × 10, 42.67 × 10and 65.8 × 10maduring the periods 1974–92, 1992–99 and 1999–2010, respectively. Other non-glacier-fed lakes in the vicinity (i.e. Longwei Co, Amur Co and Darngo Co Ngion) shrank considerably from the early 1970s to 1992 and then expanded from 1992 to 2010. Despite being in the same climate region, Linggo Co and the non-glacier-fed lakes have differed in response to climate change. The glaciers in the catchment of Linggo Co retreated by 2.4% in area between 1974 and 2007, and their mean thickness decreased by 6.19 ± 1.91 m between 1974 and 2000, with an associated glacier meltwater runoff of (7.52 ± 2.32) × 10m. The results indicate that glacier mass loss had a significant impact on the growth of Linggo Co over the past 40 years.
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| [25] |
Climate change driven water budget dynamics of a Tibetan inland lake [J].https://doi.org/10.1016/j.gloplacha.2017.02.003 URL [本文引用: 3] 摘要
61Precipitation is the main factor controlling the water balance and lake level variability of Lake Nam Co.61A lumped lake-watershed model was improved for water budget analysis of the Tibetan lakes.61Contributions of the individual hydrologic components to the water balance of a Tibetan lake (Nam Co) were examined.61There is groundwater outflow (water seepage) in Lake Nam Co.
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| [26] |
Recent decadal glacier mass balances over the Western Nyainqentanglha Mountains and the increase in their melting contribution to Nam Co Lake measured by differential Bistatic SAR interferometry [J].https://doi.org/10.1016/j.gloplacha.2016.12.018 URL [本文引用: 1] 摘要
The Western Nyainqentanglha Mountains locates in the southeastern center of the Inner Tibetan Plateau (ITP). Glaciers in this region are influenced by both the continental climate of Central Asia and the Indian Monsoon system. Their melting on the western slopes feeds the Nam Co Lake, which is the second largest endorheic lake in the ITP. The elevation of Nam Co Lake increased at a rate of 0.2502±020.1202m02year 61021 from 2003 to 2009. In this study, aimed at quantifying the decadal glacier mass balance in the Western Nyainqentanglha Mountains and their increasing melting contribution to Nam Co Lake; we applied the differential Bistatic SAR interferometry method to five pairs of TanDEM CoSSC datasets observed between 2013 and 2014 and SRTM acquired in 2000. The mean annual mass loss rate was 61020.23502±020.12702m02w.e.02year 61021 for the entire range. The mass loss rate for the northwestern slope (inside the Nam Co Lake drainage basin) and the southeastern slope (outside the Nam Co Lake drainage basin) were 61020.26802±020.12902m02w.e.02year 61021 and 01020.21902±020.12602m02w.e.02year 61021 , respectively. Our results agree well with previous fieldwork at the Zhadang and Gurenhekou glaciers located on the northwestern and southeastern slopes. Debris-cover suppressed glacier downwasting to some extent. By presuming that all of the melted ice flows into the lake, the glaciers' melting contribution to Nam Co Lake's increasing water volume was approximately 10.5002±029.00% during the period between 2003 and 2009.
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| [27] |
An automated scheme for glacial lake dynamics mapping using Landsat imagery and digital elevation models: A case study in the Himalayas [J].https://doi.org/10.1080/01431161.2012.657370 URL [本文引用: 1] 摘要
Glacial lakes in alpine regions are sensitive to climate change. Mapping and monitoring these lakes would improve our understanding of regional climate change and glacier-related hazards. However, glacial lake mapping over large areas using remote sensing remains a challenge because of various disturbing factors in glacial and periglacial environments. This article presents an automated mapping algorithm based on hierarchical image segmentation and terrain analysis to delineate glacial lake extents. In this algorithm, each glacial lake is delineated with a local segmentation value, and the topographic features derived from digital elevation models (DEMs) are also used to separate mountain shadows from glacial lakes. About 100 scenes of Landsat Thematic Mapper/Enhanced Thematic Mapper Plus (TM/ETM+) images from circa 1990, circa 2000 and 2009 were used to map the glacial lakes and their changes over the entire Himalayas. The results show that the algorithm can map the glacial lakes effectively and efficiently. Mountain shadows or melting glaciers can be differentiated from glacial lakes automatically, and those lakes with mountain shadows can also be identified. Area changes of more than 1000 glacial lakes show that the glacial lakes in the Himalayas have experienced mixed directions of change, while the overall lake areas are expanding at an accelerated rate in the past two decades, indicating great changes to the glacial lakes in the Himalayas.
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| [28] |
Patterns and potential drivers of dramatic changes in Tibetan lakes, 1972-2010 [J].https://doi.org/10.1371/journal.pone.0111890 URL PMID: 25372787 [本文引用: 1] 摘要
Abstract Most glaciers in the Himalayas and the Tibetan Plateau are retreating, and glacier melt has been emphasized as the dominant driver for recent lake expansions on the Tibetan Plateau. By investigating detailed changes in lake extents and levels across the Tibetan Plateau from Landsat/ICESat data, we found a pattern of dramatic lake changes from 1970 to 2010 (especially after 2000) with a southwest-northeast transition from shrinking, to stable, to rapidly expanding. This pattern is in distinct contrast to the spatial characteristics of glacier retreat, suggesting limited influence of glacier melt on lake dynamics. The plateau-wide pattern of lake change is related to precipitation variation and consistent with the pattern of permafrost degradation induced by rising temperature. More than 79% of lakes we observed on the central-northern plateau (with continuous permafrost) are rapidly expanding, even without glacial contributions, while lakes fed by retreating glaciers in southern regions (with isolated permafrost) are relatively stable or shrinking. Our study shows the limited role of glacier melt and highlights the potentially important contribution of permafrost degradation in predicting future water availability in this region, where understanding these processes is of critical importance to drinking water, agriculture, and hydropower supply of densely populated areas in South and East Asia.
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| [29] |
Multi-feature combined cloud and cloud shadow detection in GaoFen-1 wide field of view imagery [J].https://doi.org/10.1016/j.rse.2017.01.026 URL [本文引用: 1] 摘要
Abstract: The wide field of view (WFV) imaging system onboard the Chinese GaoFen-1 (GF-1) optical satellite has a 16-m resolution and four-day revisit cycle for large-scale Earth observation. The advantages of the high temporal-spatial resolution and the wide field of view make the GF-1 WFV imagery very popular. However, cloud cover is an inevitable problem in GF-1 WFV imagery, which influences its precise application. Accurate cloud and cloud shadow detection in GF-1 WFV imagery is quite difficult due to the fact that there are only three visible bands and one near-infrared band. In this paper, an automatic multi-feature combined (MFC) method is proposed for cloud and cloud shadow detection in GF-1 WFV imagery. The MFC algorithm first implements threshold segmentation based on the spectral features and mask refinement based on guided filtering to generate a preliminary cloud mask. The geometric features are then used in combination with the texture features to improve the cloud detection results and produce the final cloud mask. Finally, the cloud shadow mask can be acquired by means of the cloud and shadow matching and follow-up correction process. The method was validated using 108 globally distributed scenes. The results indicate that MFC performs well under most conditions, and the average overall accuracy of MFC cloud detection is as high as 96.8%. In the contrastive analysis with the official provided cloud fractions, MFC shows a significant improvement in cloud fraction estimation, and achieves a high accuracy for the cloud and cloud shadow detection in the GF-1 WFV imagery with fewer spectral bands. The proposed method could be used as a preprocessing step in the future to monitor land-cover change, and it could also be easily extended to other optical satellite imagery which has a similar spectral setting.
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| [30] |
Recent changes in the active layer thickness across the northern hemisphere [J].https://doi.org/10.1007/s12665-015-5229-2 URL [本文引用: 1] 摘要
中国科学院寒区旱区环境与工程研究所机构知识库(CASNW OpenIR)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。
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| [31] |
A half-century of changes in China's lakes: Global warming or human influence [J].https://doi.org/10.1029/2010GL045514 URL [本文引用: 1] 摘要
Lake size is sensitive to both climate change and human activities, and therefore serves as an excellent indicator to assess environmental changes. Using a large volume of various datasets, we provide a first complete picture of changes in China's lakes between 1960s-1980s and 2005-2006. Dramatic changes are found in both lake number and lake size; of these, 243 lakes vanished mainly in the northern provinces (and autonomous regions) and also in some southern provinces while 60 new lakes appeared mainly on the Tibetan Plateau and neighboring provinces. Limited evidence suggested that these geographically unbalanced changes might be associated primarily with climate change in North China and human activities in South China, yet targeted regional studies are required to confirm this preliminary observation.
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| [32] |
China's lakes at present: Number, area and spatial distribution [J].https://doi.org/10.1007/s11430-010-4052-6 URL [本文引用: 1] 摘要
Based on 11004 satellite images from CBERS CCD and Landsat TM/ETM,changes in the spatial characteristics of all lakes in China were determined following pre-established interpretation rules.This dataset was supported by 6843 digital raster images(1:100000 and 1:50000),a countrywide digital vector dataset(1:250000),and historical literature.Comparative data were corrected for seasonal variations using precipitation data.There are presently 2693 natural lakes in China with an area greater than 1.0 km2,excluding reservoirs.These lakes are distributed in 28 provinces,autonomous regions and municipalities and have a total area of 81414.6 km2,accounting for-0.9% of China's total land area.In the past 30 years,the number of newly formed and newly discovered lakes with an area greater than 1.0 km2 is 60 and 131,respectively.Conversely,243 lakes have disappeared in this time period.
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| [33] |
The use of the normalized difference water index (NDWI) in the delineation of open water features [J].https://doi.org/10.1080/01431169608948714 URL [本文引用: 2] 摘要
The Normalized Difference Water Index (NDWI) is a new method that has been developed to delineate open water features and enhance their presence in remotely-sensed digital imagery. The NDWI makes use of reflected near-infrared radiation and visible green light to enhance the presence of such features while eliminating the presence of soil and terrestrial vegetation features. It is suggested that the NDWI may also provide researchers with turbidity estimations of water bodies using remotely-sensed digital data.
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| [34] |
Glacier mass changes on the Tibetan Plateau 2003-2009 derived from ICESat laser altimetry measurements [J].https://doi.org/10.1088/1748-9326/9/1/014009 URL [本文引用: 2] 摘要
Glacier mass changes are a valuable indicator of climate variability and monsoon oscillation on the underexplored Tibetan Plateau. In this study data from the Ice Cloud and Elevation Satellite (ICESat) is employed to estimate elevation and mass changes of glaciers on the Tibetan Plateau between 2003 and 2009. In order to get a representative sample size of ICESat measurements, glaciers on the Tibetan Plateau were grouped into eight climatically homogeneous sub-regions. Most negative mass budgets of - 0.77 ± 0.35 m w.e. awere found for the Qilian Mountains and eastern Kunlun Mountains while a mass gain of + 0.37 ± 0.25 m w.e. awas found in the westerly-dominated north-central part of the Tibetan Plateau. A total annual mass budget of - 15.6 ± 10.1 Gt awas estimated for the eight sub-regions sufficiently covered by ICESat data which represents 0080% of the glacier area on the Tibetan Plateau. 13.9 ± 8.9 Gt a(or 0.04 ± 0.02 mm asea-level equivalent) of the total mass budget contributed ‘directly’ to the global sea-level rise while 1.7 ± 1.9 Gt adrained into endorheic basins on the plateau.
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| [35] |
The Circumpolar-Active-Layer-Monitoring (CALM) workshop: Introduction [J].https://doi.org/10.1002/(ISSN)1099-1530 URL [本文引用: 1] |
| [36] |
Modeling the active-layer depth over the Tibetan Plateau [J].https://doi.org/10.1657/1523-0430(06-200)[OELKE]2.0.CO;2 URL [本文引用: 1] |
| [37] |
Rapid and highly variable warming of lake surface waters around the globe [J].https://doi.org/10.1002/2015GL066235 URL [本文引用: 1] 摘要
In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global mean = 0.34°C decade 1) between 1985 and 2009. Our analyses show that surface water warming rates are dependent on combinations of climate andlocal characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factors —from seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72°C decade 1) to ice-free lakes experiencing increases in air temperatureand solar radiation (0.53°C decade 1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.
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| [38] |
A threshold selection method from gray-level histograms [J].https://doi.org/10.1109/TSMC.1979.4310076 URL [本文引用: 1] |
| [39] |
Active layer thickness calculation over the Qinghai-Tibet Plateau [J].https://doi.org/10.1016/j.coldregions.2009.01.005 URL [本文引用: 1] 摘要
The rising air temperature and increased human activities have caused permafrost degradation over the Qinghai–Tibet Plateau, including thickening of the active layer. The active layer plays an important role in cold regions. Active layer thickness (hereafter ALT) variation may have profound socio-economic and eco-environmental consequences. Using a climate-driven model based on Kudryavtsev's formulations and data from climate records, snow and vegetation parameters, and soil features, we calculated ALTs of the permafrost regions over the Qinghai–Tibet Plateau. A general agreement was found when comparing the calculated results with measured values at survey sites. A distribution map of ALT over the Qinghai–Tibet Plateau shows that ALTs in the central part of the plateau are generally smaller than those in other regions while ALTs in the northern and western regions are larger than those in the eastern and southern regions of the plateau. ALTs of the permafrost regions along the Qinghai–Tibet Highway are generally larger than 2.002m. The regions with ALTs less than 2.002m are mainly in the high-mountain areas.
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| [40] |
High-resolution mapping of global surface water and its long-term changes [J].https://doi.org/10.1038/nature20584 URL PMID: 27926733 [本文引用: 1] 摘要
Abstract The location and persistence of surface water (inland and coastal) is both affected by climate and human activity and affects climate, biological diversity and human wellbeing. Global data sets documenting surface water location and seasonality have been produced from inventories and national descriptions, statistical extrapolation of regional data and satellite imagery, but measuring long-term changes at high resolution remains a challenge. Here, using three million Landsat satellite images, we quantify changes in global surface water over the past 32 years at 30-metre resolution. We record the months and years when water was present, where occurrence changed and what form changes took in terms of seasonality and persistence. Between 1984 and 2015 permanent surface water has disappeared from an area of almost 90,000 square kilometres, roughly equivalent to that of Lake Superior, though new permanent bodies of surface water covering 184,000 square kilometres have formed elsewhere. All continental regions show a net increase in permanent water, except Oceania, which has a fractional (one per cent) net loss. Much of the increase is from reservoir filling, although climate change is also implicated. Loss is more geographically concentrated than gain. Over 70 per cent of global net permanent water loss occurred in the Middle East and Central Asia, linked to drought and human actions including river diversion or damming and unregulated withdrawal. Losses in Australia and the USA linked to long-term droughts are also evident. This globally consistent, validated data set shows that impacts of climate change and climate oscillations on surface water occurrence can be measured and that evidence can be gathered to show how surface water is altered by human activities. We anticipate that this freely available data will improve the modelling of surface forcing, provide evidence of state and change in wetland ecotones (the transition areas between biomes), and inform water-management decision-making.
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| [41] |
Asia’s glaciers are a regionally important buffer against drought [J].https://doi.org/10.1038/nature22062 URL PMID: 28492255 [本文引用: 1] 摘要
The high mountains of Asia ncompassing the Himalayas, the Hindu Kush, Karakoram, Pamir Alai, Kunlun Shan, and Tian Shan mountains ave the highest concentration of glaciers globally, and 800 million people depend in part on meltwater from them. Water stress makes this region vulnerable economically and socially to drought, but glaciers are a uniquely drought-resilient source of water. Here I show that these glaciers provide summer meltwater to rivers and aquifers that is sufficient for the basic needs of 136 million people, or most of the annual municipal and industrial needs of Pakistan, Tajikistan, Turkmenistan, Uzbekistan and Kyrgyzstan. During drought summers, meltwater dominates water inputs to the upper Indus and Aral river basins. Uncertainties in mountain precipitation are poorly known, but, given the magnitude of this water supply, predicted glacier loss would add considerably to drought-related water stress. Such additional water stress increases the risk of social instability, conflict and sudden, uncontrolled population migrations triggered by water scarcity, which is already associated with the large and rapidly growing populations and hydro-economies of these basins.
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| [42] |
China: The third pole [J].https://doi.org/10.1038/454393a URL [本文引用: 1] |
| [43] |
Mapping surface temperature in large lakes with MODIS data [J].https://doi.org/10.1016/j.rse.2007.05.015 URL [本文引用: 1] 摘要
Satellite sensor MODIS on two platforms can produce Sea Surface Temperature over certain regions about three to four times per day. Our objective was to test if the MODIS SST product can be applied for lakes whose surface areas are large enough to be observed at the MODIS spatial resolution and to compare the satellite-derived lake surface temperatures with in situ measurements. Surface temperatures for Lakes V01nern and V01ttern in Sweden, two of the largest European lakes, are extracted from the MODIS/Terra images for period 2001–2003. The results are analyzed on different quality levels, as all MODIS L2 products are equipped with an additional quality flag. We present temperature development over 2001–2003, and show the capability of the MODIS SST product to couple the known thermodynamical features in the lakes under study, where temperature varies greatly with space and time. These results can complement lake monitoring programs anywhere.
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| [44] |
Terra and aqua MODIS products available from NASA GES DAAC [J].https://doi.org/10.1016/j.asr.2004.03.012 URL [本文引用: 1] 摘要
The NASA Goddard Earth Sciences Distributed Active Archive Center (GES DAAC), known as GSFC-ECS in the Earth Observing System Data Gateway, distributes three major groups of MODIS products: Level 1 Radiometric and Geolocation data, and Level 2 and higher level of Atmosphere and Ocean products. The Atmosphere data types are aerosol, water vapor, cloud, temperature and moisture profiles, and cloud mask. The 107 (at present) Ocean data types include such parameters as normalized water-leaving radiances, chlorophyll and pigment concentrations (“ocean color”), total absorptions, sea surface temperatures, and ocean primary productivity. GES DAAC provides a broad spectrum of MODIS support, covering; data access, visualization tools, tools for search and order of the aforementioned data, documentation, data content, troubleshooting, and science and software support for the Earth Observing System Core System (ECS). The Web gateway for MODIS data products and services is http://daac.gsfc.nasa.gov/MODIS/
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| [45] |
Satellite observations indicate rapid warming trend for lakes in California and Nevada [J].https://doi.org/10.1029/2009GL040846 URL [本文引用: 2] 摘要
Large lake temperatures are excellent indicators of climate change; however, their usefulness is limited by the paucity of in situ measurements and lack of long-term data records. Thermal infrared satellite imagery has the potential to provide frequent and accurate retrievals of lake surface temperatures spanning several decades on a global scale. Analysis of seventeen years of data from the Al...
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| [46] |
Modeling and analysis of lake water storage changes on the Tibetan Plateau using multi-mission satellite data [J].https://doi.org/10.1016/j.rse.2013.03.013 URL [本文引用: 1] 摘要
Estimation of the water storage changes in the lakes of the Tibetan Plateau (TP) is essential for an accurate evaluation of climate change in this alpine region and its impact on the surrounding hydrologic environment. Because of the remoteness and poor accessibility of these alpine lakes, and a lack of lake bathymetric data, estimating their mass budget over the TP poses a considerable challenge. However, the integration of optical remote sensing images, satellite altimetry data, and gravimetry data makes it possible to monitor the overall variations in lake water storage in this extensive region. The ICESat/GLAS altimetry data used in this study reveal that most of the lakes in the TP showed a significant upward tendency (0.2–0.602m/year) in water level between 2003 and 2009, particularly those lakes that are supplied with a large proportion of glacial meltwater. A series of lake area data derived from Landsat MSS/TM/ETM02+02imagery over the past four decades indicate that during the 1970–1990 period most of the lakes experienced severe shrinkage, with only some of those in central and western Tibet undergoing expansion. During the 1990–2011 period, in contrast, the majority of the lakes on the TP displayed a remarkably expansion tendency. The total lake area increased from 35,638.1102km 2 in the early 1970s to 41,938.6602km 2 in 2011. Based on the statistical relationships between the extent of the lake surface area and lake water levels from 2003 to 2009, an empirical model for each of the region's 30 lakes is established to estimate the lake water level from the corresponding area data, thereby reconstructing time series of lake level data for each lake from the 1970s to 2011. Based on time series of lake area and water level data, a time series of lake water volume is also reconstructed. The results show that total lake water storage increased by 92.4302km 3 between the early 1970s and 2011, with lakes with an area larger than 10002km 2 accounting for 77.21% of the total lake water volume budget. Moreover, the GRACE signals confirm a similar spatial pattern in water mass changes, i.e., a significantly positive water mass balance in the north and center of the TP and mass loss in southeastern Tibet and along the Himalayas. The water mass budget (6.8102km 3 /year) derived from satellite gravimetry signals in the Chiangtang Plateau are in good agreement with the estimated rising rate of 6.7902km 3 /year of lake water storage in this region based on the empirical model developed in this study. The mechanism of lake water storage changes is discussed and analyzed with reference to previous studies.
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| [47] |
Accelerated lake expansion on the Tibetan Plateau in the 2000s: Induced by glacial melting or other processes [J].https://doi.org/10.1002/2013WR014724 URL [本文引用: 1] 摘要
ccelerated lake expansion in the 2000s has been confirmed by both dramatic lake-area increases (for 312 lakes larger than 10 km2) derived from optical images, and rapid water-level rises (for 117 lakes with water-level data) measured by satellite altimetry. However, the underlying climate causes remain unclear. This paper analyzes the relationship between the water-level changes of lakes on the plateau and the potential driving factors, such as the glacier meltwater supply and a dependency on precipitation and runoff over the whole plateau and in each zone. The results show that the rates of change of non-glacier-fed lakes in the 2000s were as high as those of glacier-fed lakes across the whole plateau and the lake-level changes were closely associated with the lake supply coefficients (the basin/lake area ratio). The lake variations agreed well with the spatial pattern of precipitation changes. However, in different zones, especially at around 33 N north of the plateau, glacier-fed lakes did exhibit faster lake level increases than no-glacier-fed lakes, indicating that the presence of a glacier meltwater supply augmented the precipitation-driven lake expansions in these areas. Despite the absence of quantitative modeling due to limited data availability, this study provides qualitative support that the lake expansions on the Tibetan Plateau in the 2000s have been driven primarily by changes in precipitation and evapotranspiration and not solely by the effect of glacier wastage.
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| [48] |
Impact of global warming on permafrost conditions in a coupled GCM [J].https://doi.org/10.1029/2001GL014345 URL [本文引用: 1] 摘要
Permafrost currently underlies nearly a quarter of the exposed land area of the North- ern Hemisphere. A climate change scenario experiment conducted with the state- of-the-art coupled atmosphere-ocean general circulation model ECHAM4/OPYC3 is analysed with the objective to quantify changes in Arctic permafrost conditions. We propose an efficient procedure which overcomes the many problems associated with an explicit treatment of soil freezing and thawing processes. The zero degree soil tem- perature as well as induced permafrost index characteristics simulated by the model for present-day conditions match well the observed permafrost zonation. For future scenarios of greenhouse gas emissions (SRES A2 and B2 issued by IPCC), we es- timate the amounts that the permafrost zones move poleward and how the thickness of the active layer deepens in response to the global warming by the end of the 21st century.
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| [49] |
Rapid loss of lakes on the Mongolian Plateau [J].https://doi.org/10.1073/pnas.1411748112 URL PMID: 25646423 [本文引用: 1] 摘要
Abstract Lakes are widely distributed on the Mongolian Plateau and, as critical water sources, have sustained Mongolian pastures for hundreds of years. However, the plateau has experienced significant lake shrinkage and grassland degradation during the past several decades. To quantify the changes in all of the lakes on the plateau and the associated driving factors, we performed a satellite-based survey using multitemporal Landsat images from the 1970s to 2000s, combined with ground-based censuses. Our results document a rapid loss of lakes on the plateau in the past decades: the number of lakes with a water surface area >1 km(2) decreased from 785 in the late 1980s to 577 in 2010, with a greater rate of decrease (34.0%) in Inner Mongolia of China than in Mongolia (17.6%). This decrease has been particularly pronounced since the late 1990s in Inner Mongolia and the number of lakes >10 km(2) has declined by 30.0%. The statistical analyses suggested that in Mongolia precipitation was the dominant driver for the lake changes, and in Inner Mongolia coal mining was most important in its grassland area and irrigation was the leading factor in its cultivated area. The deterioration of lakes is expected to continue in the following decades not only because of changing climate but also increasing exploitation of underground mineral and groundwater resources on the plateau. To protect grasslands and the indigenous nomads, effective action is urgently required to save these valuable lakes from further deterioration.
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| [50] |
Quantifying the contribution of glacier meltwater in the expansion of the largest lake in Tibet [J].https://doi.org/10.1002/2016JD025424 URL [本文引用: 2] 摘要
Abstract The Lake Siling Co is currently the largest endorheic lake in Tibet and the lake surface area has expanded by about 40% since the 1970s, with a remarkable acceleration after 1999. In this study, a hydrologic modeling framework was established by linking the Variable Infiltration Capacity (VIC) land surface hydrologic model with the degree-day glacier-melt model over the Lake Siling Co basin, with the aim to quantify the contribution of each runoff component to changes in the lake storage. We found that glacier melt contributed to less than 10% of the total water input to the lake during 1979–2013, while precipitation-induced runoff in non-glacierized area was responsible for about 67–75%. The mean annual water input to the lake increased by 2.15 × 109 m3 yr611 in 2000–2013 relative to that in 1979–1999. The amount of precipitation over the lake surface, precipitation-induced runoff, and glacier-melt runoff accounted for 13%, 82% and 5% of this total increase, respectively, suggesting that the substantial expansion of Siling Co in the 2000s was mostly due to the increase in precipitation-induced runoff. When modeling lake level changes during 1979–2013, we found that the water level rose by 14.1 m when glacier melt was included and only 10.5 m, a reduction of about 1/4, when glacier melt was removed. It is concluded that glacier melt played an important role in controlling the water level of Siling Co, although it only contributed less than 10% of water input to the lake during 1979–2013.
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| [51] |
A survey of ICESat coastal altimetry applications: Continental coast, open ocean island, and inland river [J].https://doi.org/10.3319/TAO.2008.19.1-2.1(SA) URL [本文引用: 1] 摘要
ICESat satellite laser altimetry provides an unprecedented set of global elevation measurements of the Earth, yielding great detail over ice, land and ocean surfaces. Coastal regions in particular, including seamless land-water transitions, benefit from the small footprint (50 to 90 m), high resolution (40 Hz, ~170 m along-track), and high precision (2 to 3 cm) of ICESat. We discuss the performance and character of ICESat data in three example coastal scenarios: continental coast (Louisiana-Mississippi Gulf Coast, USA, including Lake Pontchartrain), open ocean island (Funafuti, Tuvalu), and an inland river (confluence of Tapajos and Amazon rivers, Brazil). Water elevations are compared to tide gauge heights and to TOPEX and Jason-1 radar altimetry. In demonstrating the utilization of ICESat, we also present examples of: laser waveform shapes over a variety of surface types (water, land, and vegetation); vegetation canopy heights (detecting large-scale destruction from Hurricane Katrina comparing data before and after); sub-canopy surface water; measurements of waves; and examination of along-stream river slope and comparisons of river stage to hydrologically-driven GRACE geoid change.
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| [52] |
A generalized split-window algorithm for retrieving land-surface temperature from space [J].https://doi.org/10.1109/36.508406 URL [本文引用: 1] |
| [53] |
Preliminary estimate of calibration of the moderate resolution imaging spectroradiometer thermal infrared data using Lake Titicaca [J].https://doi.org/10.1016/S0034-4257(01)00327-3 URL [本文引用: 1] 摘要
The absolute radiometric accuracy of Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared (TIR) data was evaluated with in situ data collected in a vicarious calibration field campaign conducted in Lake Titicaca, Bolivia during May 26 and June 17, 2000. The comparison between MODIS TIR data produced by the version 2.5.4 Level-1B code and the band radiances calculated with atmospheric radiative transfer code MODTRAN4.0 based on lake surface kinetic temperatures measured by five IR radiometers deployed in the high-elevation Lake Titicaca and the atmospheric temperature and water vapor profiles measured by radiosondes launched on the lake shore on June, 15 2000, a calm clear-sky day, shows good agreements in bands 31 and 32 (within an accuracy of 0.4%) in the daytime overpass case. Sensitivity analysis indicates that the changes on the measured atmospheric temperature and water vapor profiles result in negligible or small effects on the calculated radiances in the atmospheric window bands (bands 20–23, 29, and 31–32). Therefore, comparisons for these bands were made for cases when lake surface temperature measurements were available but no radiosonde data were available and in subareas of 10×16 pixels where there was no in situ measurement but MODIS brightness temperatures in band 31 vary within ±0.15 K by using the validated band 31 to determine lake surface temperatures through the MODTRAN4.0 code. Comparisons and error analysis show that the specified absolute radiometric accuracies are reached or nearly reached in MODIS bands 21, 29, and 31–33 and that there is a calibration bias of 2–3% in bands 20, 22, and 23. The error analysis also shows that the radiosondes cannot provide accurate atmospheric temperature and water vapor profiles to estimate the calibration accuracies in the atmospheric sounding bands (bands 24–25, 27–28, and 34–36) at the specified 1% level and that the calibration accuracy in the ozone band 30 cannot be estimated without in situ measurements of ozone.
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| [54] |
Validation of the land-surface temperature products retrieved from Terra moderate resolution imaging spectroradiometer data [J].https://doi.org/10.1016/S0034-4257(02)00093-7 URL [本文引用: 1] 摘要
This paper presents the status of land-surface temperature (LST) standard products retrieved from Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) data. Based on estimates of the channel-dependence error and noise equivalent temperature difference (NEDT) and the calibration accuracy of MODIS thermal nfrared data, the impact of instrument performance on the accuracy of LST is discussed. A double-screen scheme based on the difference between the 5-km LST retrieved by the day/night LST algorithm and the aggregated 1-km LST retrieved by the generalized split-window algorithm, and the difference between daytime and nighttime LSTs, is proposed to remove the LSTs contaminated with cloud effects. The accuracy of daily MODIS LST product at 1-km resolution, which was produced by the generalized split-window algorithm, was validated in 11 clear-sky cases with in situ measurement data collected in field campaigns in 2000 and 2001. The MODIS LST accuracy is better than 1 K in the range from 263 to 300 K over Lake Titicaca in Bolivia, Mono Lake, Bridgeport grassland, and a rice field in Chico, CA, and Walker Lake, Nevada (NV), in the atmospheric column water vapor range from 0.4 to 3.0 cm. It is difficult to validate the daytime LST product over land sites rather than lakes with ground-based measurements alone because of the high spatial variations in the in situ LST measurement data, which was verified by the daytime data of the MODIS Airborne Simulator (MAS) over a grassland in Bridgeport, CA, on October 6, 2000. In six cases over a silt playa in Railroad Valley, NV, the 1-km MODIS LSTs are a few Kelvin degrees lower than the in situ measured LSTs because the surface emissivities inferred from land cover types in the split-window LST method are often overestimated in semi-arid and arid regions. After a correction with the difference between the 5-km LST retrieved by the day/night LST method and the LST aggregated from 1-km LSTs retrieved by the split-window method, the MODIS LSTs agree with in situ measured LSTs within 1 K in the range 263 322 K for the six cases in Railroad Valley and one case of snowcover in Bridgeport, CA, leading a recommendation for use of the 5-km LST product retrieved by the day/night LST method in bare and sparse vegetated areas.
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| [55] |
Changes in active-layer thickness and near-surface permafrost between 2002 and 2012 in alpine ecosystems, Qinghai-Xizang (Tibet) Plateau, China [J].https://doi.org/10.1016/j.gloplacha.2014.09.002 URL [本文引用: 1] 摘要
Between 2002 and 2012, daily soil temperature measurements were made at 10 sites within five alpine ecosystems in the Beiluhe area of the central Qinghai–Tibet Plateau. Changes in freeze–thaw occurrence, active-layer thickness and near-surface permafrost temperature in barren, desert grassland, alpine steppe and alpine meadow ecosystems indicate that alpine ecosystems are sensitive to climate variability. During this time, the average onset of spring thawing at 50-cm depth advanced by at least 1602days in all but the barren alpine settings, and the duration of thaw increased by at least 1402days for all but the desert grassland and barren ecosystems. All sites showed an increase in active-layer thickness (ALT) and near-surface permafrost temperature: the average increase of ALT was ~024.2602cm/a and the average increase in permafrost temperatures at 602m and 1002m depths were, respectively, ~020.1302°C and ~020.1402°C. No apparent trend in mean annual air temperature was detected at the Beiluhe weather station. However, an increasing trend in precipitation was measured. This suggests that the primary control on the ALT increase was an increase in summer rainfall and the primary control on increasing permafrost temperature was probably the combined effects of increasing rainfall and the asymmetrical seasonal changes in subsurface soil temperatures.
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| [56] |
Long-term changes of lake level and water budget in the Nam Co Lake Basin, Central Tibetan Plateau [J].https://doi.org/10.1175/JHM-D-13-093.1 URL [本文引用: 1] 摘要
Long-term changes in the water budget of lakes in the Tibetan Plateau due to climate change are of great interest not only for the importance of water management, but also for the critical challenge due to the lack of observations. In this paper, the water budget of Nam Co Lake during 1980-2010 is simulated using a dynamical monthly water balance model. The simulated lake level is in good agreement with field investigations and the remotely sensed lake level. The long-term hydrological simulation shows that from 1980 to 2010, lake level rose from 4718.34 to 4724.93 m, accompanied by an increase of lake water storage volume from 77.33 X 10(9) to 83.66 X 10(9) m(3). For the net lake level rise (5.93 m) during the period 1980-2010, the proportional contributions of rainfall runoff, glacier melt, precipitation on the lake, lake percolation, and evaporation are 104.7%, 56.6%, 41.7%, -22.2%, and -80.9%, respectively. A positive but diminishing annual water surplus is found in Nam Co Lake, implying a continuous but slowing rise in lake level as a hydrological consequence of climate change.
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| [57] |
Modification of normalised difference water index (NDWI) to enhance open water features in remotely sensed imagery [J].https://doi.org/10.1080/01431160600589179 URL [本文引用: 4] 摘要
The normalized difference water index (NDWI) of McFeeters (1996) was modified by substitution of a middle infrared band such as Landsat TM band 5 for the near infrared band used in the NDWI. The modified NDWI (MNDWI) can enhance open water features while efficiently suppressing and even removing built‐up land noise as well as vegetation and soil noise. The enhanced water information using the NDWI is often mixed with built‐up land noise and the area of extracted water is thus overestimated. Accordingly, the MNDWI is more suitable for enhancing and extracting water information for a water region with a background dominated by built‐up land areas because of its advantage in reducing and even removing built‐up land noise over the NDWI.
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| [58] |
Recent glacial retreat and its impact on hydrological processes on the Tibetan Plateau, China, and surrounding regions [J].https://doi.org/10.1657/1523-0430(07-510)[YAO]2.0.CO;2 URL [本文引用: 1] 摘要
Glacial retreat on the Tibetan Plateau and surrounding regions is characteristic since the 1960s and has intensified in the past 10 yr. The magnitude of glacial retreat is relatively small in the interior of the Tibetan Plateau and increases to the margins of the plateau, with the greatest retreat around the edges. Glacial retreat in this region is impacting the hydrological processes in the Tibetan Plateau and surrounding regions. The glacial retreat has caused an increase of more than 5.5% in river runoff from the plateau. In some areas, such as the Tarim River basin, the increase in river runoff is greater. Glacial retreat has also caused rising lake levels in the areas with large coverage of glaciers, such as the Nam Co Lake and Selin Co Lake areas. Rising lake levels are devastating grasslands and villages near the lakes.
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| [59] |
Different glacier status with atmospheric circulations in Tibetan Plateau and surroundings [J].https://doi.org/10.1038/nclimate1580 URL [本文引用: 4] 摘要
The Tibetan Plateau and surroundings contain the largest number of glaciers outside the polar regions1. These glaciers are at the headwaters of many prominent Asian rivers and are largely experiencing shrinkage2, which affects the water discharge of large rivers such as the Indus3, 4. The resulting potential geohazards5, 6 merit a comprehensive study of glacier status in the Tibetan Plateau and surroundings. Here we report on the glacier status over the past 30 years by investigating the glacial retreat of 82 glaciers, area reduction of 7,090 glaciers and mass-balance change of 15 glaciers. Systematic differences in glacier status are apparent from region to region, with the most intensive shrinkage in the Himalayas (excluding the Karakorum) characterized by the greatest reduction in glacial length and area and the most negative mass balance. The shrinkage generally decreases from the Himalayas to the continental interior and is the least in the eastern Pamir, characterized by the least glacial retreat, area reduction and positive mass balance. In addition to rising temperature, decreased precipitation in the Himalayas and increasing precipitation in the eastern Pamir accompanied by different atmospheric circulation patterns is probably driving these systematic differences.
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| [60] |
Basin mass dynamic changes in China from GRACE based on a multibasin inversion method [J].https://doi.org/10.1002/2015JB012608 URL [本文引用: 1] 摘要
Complex landforms, miscellaneous climates, and enormous populations have influenced various geophysical phenomena in China, which range from water depletion in the underground to retreating glaciers on high mountains and have attracted abundant scientific interest. This paper, which utilizes gravity observations during 2003-2014 from the Gravity Recovery and Climate Experiment (GRACE), intends to comprehensively estimate the mass status in 16 drainage basins in the region. We propose a multibasin inversion method that features resistance to stripe noise and an ability to alleviate signal attenuation from the truncation and smoothing of GRACE data. The results show both positive and negative trends. Tremendous mass accumulation has occurred from the Tibetan Plateau (12.1 0.6 Gt/yr) to the Yangtze River (7.7 1.3 Gt/yr) and southeastern coastal areas, which is suggested to involve an increase in the groundwater storage, lake and reservoir water volume, and the flow of materials from tectonic processes. Additionally, mass loss has occurred in the Huang-Huai-Hai-Liao River Basin (-10.2 0.9 Gt/yr), the Brahmaputra-Nujiang-Lancang River Basin (-15.0 1.1 Gt/yr), and Tienshan Mountain (-4.1 0.3 Gt/yr), a result of groundwater pumping and glacier melting. Areas with groundwater depletion are consistent with the distribution of cities with land subsidence in North China. We find that intensified precipitation can alter the local water supply and that GRACE can adequately capture these dynamics, which could be instructive for China's South-to-North Water Diversion hydrologic project.
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| [61] |
Developing daily cloud-free snow composite products from MODIS Terra-Aqua and IMS for the Tibetan Plateau [J].https://doi.org/10.1109/TGRS.2015.2496950 URL [本文引用: 2] 摘要
Daily snow cover mapping is difficult when Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products are cloud obscured. The daily cloud-free snow cover product provides an essential parameter for hydrological modeling, climate system studies, and snow-caused disaster monitoring on the Tibetan Plateau (TP). In this paper, we present an algorithm, Terra-Aqua-IMS (TAI), which combines MODIS Terra and Aqua (500 m) and the Interactive Multisensor Snow and Ice Mapping System (IMS; 4 km) to produce a daily cloud-free snow cover product (500 m). The overall accuracy of the new TAI over the TP is 94% as compared with ground stations in all-sky conditions; this value is significantly higher than the 64% of the blended MODIS Terra-Aqua product and the 55% and 50% of the original MODIS Terra and Aqua products, respectively. Without the IMS, the daily combination of MODIS Terra-Aqua can only remove limited cloud contamination: 37.3% of the annual mean cloud coverage compared with 46.6% (MODIS Terra) and 55.1% (MODIS Aqua). The resulting annual mean snow cover over the TP from the daily TAI data is 19.1%, which is much larger than the 4.7%-8.1% from the daily original MODIS Terra/Aqua and the blended Terra-Aqua snow product due to cloud blockage.
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| [62] |
Lake-area mapping in the Tibetan Plateau: an evaluation of data and methods [J].https://doi.org/10.1080/01431161.2016.1271478 URL [本文引用: 2] 摘要
Lake area derived from remote-sensing data is a primary data source, because changes in lake number and area are sensitive indicators of climate change. These indicators are especially useful when the climate change is not convoluted with a signal from direct anthropogenic activities. The data used for lake-area mapping is important, to avoid introducing unnecessary uncertainty into long-term trends of lake-area estimates. The methods for identifying waterbodies from satellite data are closely linked to the quality and efficiency of surface-water differentiation. However, few studies have comprehensively considered the factors affecting the selection of data and methods for mapping lake area in the Tibetan Plateau (TP), nor of evaluating their consequences. This study tests the dominant data sets (Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) data) and the methods for automated waterbody mapping on 14 large lakes (>500 km2) distributed across different climate zones of the TP. Seasonal changes in lake area and data availability from Landsat imagery are evaluated. Data obtained in October is optimal because in this month the lake area is relatively stable. The data window can be extended to September and November if insufficient data is available in October. Grouping data into three-year bins decreases the effects of year-to-year seasonal variability and provides a long-term trend that is suitable for time series analysis. The Landsat data (Multispectral Scanner, MSS; Thematic Mapper, TM; Enhanced Thematic Mapper Plus, ETM+; and Operational Land Imager, OLI) and MODIS data (MOD09A1) showed good performance for lake-area mapping. The Otsu method is used to determine the optimal threshold for distinguishing water from non-water features. Several water extraction indices, namely NDWIMcFeeters, NDWIXu, and AWEInon-shadow, yielded high overall classification accuracy (92%), kappa coefficient (0.83), and user s accuracy (~90%) for lake-water classification using Landsat data. The MODIS data using NDWIMcFeeters and NDWIXu showed consistent lake area (r2 = 0.99) compared with Landsat data on the corresponding date with root mean square error (RMSE) values of 86.87 and 103.33 km2 and mean absolute error (MAE) values of 25.7 and 29.04 km2, respectively. The MODIS data is suitable for great lake mapping, which is the case for the large lakes in the TP. Although automated water extraction indices exhibited high accuracy in separating water from non-water, visual examination and manual editing are still necessary. Combined with recent Chinese high-resolution satellites, these remotely sensed imageries will provide a wealth of data for studies of lake dynamics and long-term lake evolution in the TP.
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| [63] |
Water level variation of Lake Qinghai from satellite and in situ measurements under climate change [J].https://doi.org/10.1117/1.3601363 URL [本文引用: 2] |
| [64] |
Monitoring lake level changes on the Tibetan Plateau using ICESat altimetry data (2003-2009) [J].https://doi.org/10.1016/j.rse.2011.03.005 URL [本文引用: 6] 摘要
In this study, ICESat altimetry data are used to provide precise lake elevations of the Tibetan Plateau (TP) during the period of 2003–2009. Among the 261 lakes examined ICESat data are available on 111 lakes: 74 lakes with ICESat footprints for 4–702years and 37 lakes with footprints for 1–302years. This is the first time that precise lake elevation data are provided for the 111 lakes. Those ICESat elevation data can be used as baselines for future changes in lake levels as well as for changes during the 2003–2009 period. It is found that in the 74 lakes (56 salt lakes) examined, 62 (i.e. 84%) of all lakes and 50 (i.e. 89%) of the salt lakes show tendency of lake level increase. The mean lake water level increase rate is 0.2302m/year for the 56 salt lakes and 0.2702m/year for the 50 salt lakes of water level increase. The largest lake level increase rate (0.8002m/year) found in this study is the lake Cedo Caka. The 74 lakes are grouped into four subareas based on geographical locations and change tendencies in lake levels. Three of the four subareas show increased lake levels. The mean lake level change rates for subareas I, II, III, IV, and the entire TP are 0.12, 0.26, 0.19, 610.11, and 0.202m/year, respectively. These recent increases in lake level, particularly for a high percentage of salt lakes, supports accelerated glacier melting due to global warming as the most likely cause.
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| [65] |
Snow cover dynamics of four lake basins over Tibetan Plateau using time series MODIS data (2001-2010) [J].https://doi.org/10.1029/2012WR011971 URL [本文引用: 1] 摘要
Snow over the Tibetan Plateau (TP) is an important water source of major Asian rivers and greatly influences water availability in the downstream areas. In this study, snow cover dynamics of the four characteristic lake basins, Cedo Caka, Selin Co, Nam Co, and Yamzhog Yumco during hydrological years 2001-2010 (September through August) are examined at the basin scale using the flexible multiday combined MODIS snow cover products. The time series of multiday, seasonal, and annual snow covered area (SCA), onset/disappearance dates of snow, snow covered days (SCD), peaks of maximum SCA, and snow cover index (SCI) for each hydrological year (HY) are examined. Results show there is no obvious trend of snow cover change in the examined period, although Nam Co basin has the greatest SCA in all four basins and in all years, and Cedo Caka and Selin Co basins show the smallest SCA in most of the years. Overall, the HY2007 shows a greater snow extent and HY2010 a smaller for the region, with exceptions for the Nam Co basin where the HY2003 is the greatest and for Cedo Caka basin where the HY2004 is the smallest. Statistical analysis between lake level changes and lake basin's SCA, precipitation and pan evaporation (ET) changes shows that (1) Cedo Caka's water level rise was highly correlated with the basin's SCA changes (r = 0.94, p = 0.063); (2) Selin Co's water level rise was significantly correlated with the basin's SCA, precipitation and ETchanges (r = 0.99, p = 0.029); and (3) lake level changes of Nam Co and Yamzhog Yumco were correlated with their corresponding lake basin's SCA, precipitation and ETchanges (r = 0.87 and r = 0.86, respectively), although insignificant at the 95% level. This could have been due to precipitation and ETdata of a distant meteorological station for Nam Co lake basin and the complex hydrological processes in the Yamzhog Yumco basin. This study suggests that the examination of time series snow cover dynamics is important to evaluate the water budget of lake basins with snow as a major component of water balance.
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| [66] |
Water balance estimates of ten greatest lakes in China using ICESat and Landsat data [J].https://doi.org/10.1007/s11434-013-5818-y URL [本文引用: 1] |
| [67] |
Quantitative water resources assessment of Qinghai Lake basin using Snowmelt Runoff Model (SRM) [J].https://doi.org/10.1016/j.jhydrol.2014.08.022 URL [本文引用: 1] 摘要
A Snowmelt Runoff Model (SRM) is used to simulate streamflow from snowmelt in the Buha watershed within the Qinghai Lake basin for the hydrologic years 2003–2009 (from September to August). Two different precipitation products are used as inputs to examine the model and their performances: station measured precipitation and gridded APHRODITE-precipitation, with two different snow cover products, namely, flexible multiday combined MODIS Terra–Aqua (MODISMC) maps, and the standard MODIS/Terra 8-day composite (MOD10A2) product. Results show that the MODISMC product with a higher temporal resolution of 2.202days obtains slightly small bias in runoff volumes than MOD10A2 does for basin- and zone-wide simulations. The average Nash–Sutcliffe coefficient of determination ( R 2 ) is 0.73 (0.70–0.75) for basin- and zone-wide simulations. The simulated runoff with APHRODITE-precipitation is well correlated with measured runoffs ( R 2 02=020.76). The multivariate regression analysis indicates that lake level changes are significantly associated (95% level) with the following single variables: measured runoff discharge from the Buha watershed ( R m ), simulated runoff ( R s ), simulated runoff fraction from rainfall ( R s -rainfall), the snow cover area at zone B of the Buha watershed, or with a combination of multivariates: R s -rainfall02+02 P L (precipitation over the lake) and R m 02+02 P L 02+02Evaporation. These results suggest that precipitation plays a dominant role in lake level variations. Snowmelt contributed runoff shows no significant contribution to lake level variation (13% of the total runoff). This study suggests that APHRODITE-precipitation data can be used for snowmelt simulations and water resource management on the Tibetan Plateau where precipitation gauges are limited, and that the SRM is an effective tool for estimating snowmelt discharge and water resource management in high mountain regions.
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| [68] |
Extensive and drastically different alpine lake changes on Asia’s high plateaus during the past four decades [J].https://doi.org/10.1002/2016GL072033 URL [本文引用: 3] 摘要
Asia's high plateaus are sensitive to climate change and have been experiencing rapid warming over the past few decades. We found 99 new lakes and extensive lake expansion on the Tibetan Plateau during the last four decades, 1970-2013, due to increased precipitation and cryospheric contributions to its water balance. This contrasts with disappearing lakes and drastic shrinkage of lake areas on the adjacent Mongolian Plateau: 208 lakes disappeared, and 75% of the remaining lakes have shrunk. We detected a statistically significant coincidental timing of lake area changes in both plateaus, associated with the climate regime shift that occurred during 1997/1998. This distinct change in 1997/1998 is thought to be driven by large-scale atmospheric circulation changes in response to climate warming. Our findings reveal that these two adjacent plateaus have been changing in opposite directions in response to climate change. These findings shed light on the complex role of the regional climate and water cycles and provide useful information for ecological and water resource planning in these fragile landscapes.
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| [69] |
Lake volume and groundwater storage variations in Tibetan Plateau's endorheic basin [J].https://doi.org/10.1002/2017GL073773 URL [本文引用: 4] 摘要
Abstract The Tibetan Plateau (TP), the highest and largest plateau in the world, with complex and competing cryospheric-hydrologic-geodynamic processes, is particularly sensitive to anthropogenic warming. The quantitative water mass budget in the TP is poorly known. Here we examine annual changes in lake area, level, and volume during 1970s 61 2015. We find that a complex pattern of lake volume change during 1970s 61 2015: a slight decrease of –2.78 Gt yr-1 during 1970s 61 1995, followed by a rapid increase of 12.53 Gt yr-1 during 1996 61 2010, and then a recent deceleration (1.46 Gt yr-1) during 2011 61 2015. We then estimated the recent water mass budget for the Inner TP, 2003 61 2009, including changes in terrestrial water storage (TWS), lake volume, glacier mass, snow water equivalent (SWE), soil moisture, and permafrost. The dominant components of water mass budget, namely changes in lake volume (7.72 ± 0.63 Gt yr-1) and groundwater storage (5.01 ± 1.59 Gt yr-1), increased at similar rates. We find that increased net precipitation contributes the majority of water supply (74%) for the lake volume increase, followed by glacier mass loss (13%), and ground ice melt due to permafrost degradation (12%). Other term such as SWE (1%) make a relatively small contribution. These results suggest that the hydrologic cycle in the TP has intensified remarkably during recent decades.
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| [70] |
Increased mass over the Tibetan Plateau: From lakes or glaciers [J].https://doi.org/10.1002/grl.50462 URL [本文引用: 2] 摘要
The mass balance in the Inner Tibet Plateau (ITP) derived from the Gravity Recovery and Climate Experiment (GRACE) showed a positive rate that was attributed to the glacier mass gain, whereas glaciers in the region, from other field-based studies, showed an overall mass loss. In this study, we examine lake's water level and mass changes in the Tibetan Plateau (TP) and suggest that the increased mass measured by GRACE was predominately due to the increased water mass in lakes. For the 200 lakes in the TP with 4 to 7 years of ICESat data available, the mean lake level and total mass change rates were +0.14 m/yr and +4.95 Gt/yr, respectively. Compared those in the TP, 118 lakes in the ITP showed higher change rates (+0.20 m/yr and +4.28 Gt/yr), accounting for 59% area and 86% mass increase of the 200 lakes. The lake's mass increase rate in the ITP explains the 61% increased mass (similar to 7 Gt/yr) derived from GRACE [Jacob et al., 2012], while it only accounts for 53% of the total lake area in the ITP.
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| [71] |
Estimating surface temperature changes of lakes in the Tibetan Plateau using MODIS LST data [J].https://doi.org/10.1002/2014JD021615 URL [本文引用: 3] 摘要
Abstract <p>Temperature changes over the Tibetan Plateau (TP) exhibit a dependence on altitude, as observed from meteorological station data and Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data. However, little is known about the changes in water surface temperature (WST) of lakes in the TP under the warming climate conditions over the past few decades. In this study, lake WST was examined using a MODIS/Terra 8 day LST (nighttime) product (MOD11A2) over the period 2001–2012. It was found that 52 lakes included in the analysis of WST exhibited an average rate of change of 0.01265±650.033°C/yr. Of these 52 lakes, 31 lakes (60%) displayed a temperature increase with a mean warming rate of 0.05565±650.033°C/yr and 21 lakes (40%) displayed a temperature decrease with a mean cooling rate of 610.05365±650.038°C/yr. The rates of change in WST for 13 lakes were statistically significant, and these included nine warming and four cooling lakes. Of the 17 lakes with nearby weather stations, nine lakes (53%) showed faster warming than nearby air/land. The warming lakes could be attributed to locally rising air and land surface temperatures as well as other factors such as the decreased lake ice cover. The cooling lakes were mostly located at high elevations (>420065m), and the trend could have been due to increased cold water discharge to the lakes from accelerated glacier/snow melts. Therefore, both warming and cooling lake temperatures in the TP were possibly the result of increased air temperatures (0.03665±650.027°C/yr) under global warming conditions.</p>
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| [72] |
Lakes' state and abundance across the Tibetan Plateau [J].https://doi.org/10.1007/s11434-014-0258-x URL [本文引用: 3] 摘要
Understanding the changes in number and areal extent of lakes, as well as their abundance and size distribution is important for assessments of regional and global water resources, biogeochemical cycles, and changes in climate. In this study, changes in lake area greater than 102km 2 are mapped using Landsat datasets, spanning the 1970s, 1990, 2000, and 2010. In addition, high-resolution images (GeoCover Landsat mosaic 2000, with a pixel size of 14.2502m) are used for the first time to map lakes as small as 0.00102km 2 across the entire Tibetan Plateau (TP). Results show that the numbers and areal extent of individual lakes >102km 2 in size show a slight decrease between the 1970s and 1990, followed by a clear increase from 1990 to 2010. Ninety-nine new lakes are identified between the 1970s and 2010, 71 of which are found between 1990 and 2010. This indicates the accelerated glacier melt and/or increased difference of precipitation minus evaporation since the 1990s. More than 8002% of the lakes show an increase in their area between the 1970s and 2010. The lake census, using 2000 imagery, shows that there are 32,843 lakes with a total area of 43,151.0802±02411.4902km 2 , which makes up 1.402% of the total area of the TP. Around 9602% of all lakes are small, with an area 102km 2 ) account for 9602% of the total lake area. The TP is subdivided into 12 greater drainage basins, and of these the inner TP dominates in terms of the number of lakes (55.0302%), the total area of lakes (6602%), and lake density (0.026/km 2 compared to the mean, 0.011/km 2 ). A plot of lake abundance against size shows that the size distribution of lakes departs from a typical power-law distribution, but displays such a distribution at the mean elevation (4,71502m), with an r 2 value of 0.97 and a slope of 610.66. The slopes of the abundance-size equations from each of the 12 greater basins, and from all basins together, are larger than 611, supporting the inference that larger lakes, rather than the small lakes, contribute more to the total lake surface area across the TP. The lake inventory provided in this study, along with the assessment of lake size distribution, have important implications for estimates of water balance, for water resource management, and for lake area estimations in the TP.
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| [73] |
Automated water classification in the Tibetan Plateau using Chinese GF-1 WFV data [J].https://doi.org/10.14358/PERS.83.7.509 URL [本文引用: 1] 摘要
Abstract The unique climate and topography of the Tibetan Plateau produce an abundant distribution of lakes. These lakes are important indicators of climate change, and changes in lake area have critical implications for water resources and ecological conditions. Lake area change can be monitored using the huge sets of high-resolution remote sensing data available, but this demands an automatic water classification system. This study develops an algorithm for automatic water classification using Chinese GF-1 (or Gaofen-1) wide-field-of-view (WFV) satellite data. The original GF-1 WFV data were automatically preprocessed with radiometric correction and orthorectification. The single-band threshold and two global-local segmentation methods were employed to distinguish water from non-water features. Three methods of determining the optimal thresholds for normalized difference water index (NDWI) images were compared: Iterative Self Organizing Data Analysis Technique (ISODATA); global-local segmentation with thresholds specified by stepwise iteration; and the Otsu method. The water classification from two steps of global-local segmentations showed better performance than the single-band threshold and ISODATA methods. The GF-1 WFV-based lake mapping across the entire Tibetan Plateau in 2015 using the global-local segmentations with thresholds from the Otsu method showed high quality and efficiency in automatic water classification. This method can be extended to other satellite datasets, and makes the high-resolution global monitoring and mapping of lakes possible.
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| [74] |
Exploring the water storage changes in the largest lake (Selin Co) over the Tibetan Plateau during 2003-2012 from a basin-wide hydrological modeling [J].https://doi.org/10.1002/2014WR015846 URL [本文引用: 2] |
| [75] |
Quantitative analysis of lake area variations and the influence factors from 1971 to 2004 in the Nam Co basin of the Tibetan Plateau [J].https://doi.org/10.1007/s11434-010-0015-8 URL [本文引用: 1] 摘要
By using remote sensing and GIS technologies, spatial analysis and statistic analysis, we calculated the water area and volume variations of the Nam Co Lake from 1971–2004, and discussed their influence factors from the viewpoints of climatic change and water balance. Data source in this study includes bathymetric data of the lake, aerial surveyed topographic maps of 1970, remote sensing images of 1991 and 2004 in the lake catchment, meteorological data from 17 stations within 1971–2004 in the adjacent area of the lake catchment. The results showed that the lake area expanded from 1920 km 2 to 2015 km 2 during 1971 to 2004 with the mean annual increasing rate (MAIR) of 2.81 km 2 a 611 , and the lake volume augmented from 783.23×10 8 m 3 to 863.77×10 8 m 3 with the MAIR of 2.37×10 8 m 3 . Moreover, the MAIR of the lake area and volume are both higher during 1992 to 2004 (4.01 km 2 a 611 and 3.61×10 8 m 3 a 611 ) than those during 1971 to 1991 (2.06 km 2 a 611 and 1.60×10 8 m 3 a 611 ). Analyses of meteorological data indicated that the continue rising of air temperature conduced more glacier melting water. This part of water supply, together with the increasing precipitation and the descending evaporation, contributed to the enlargement of Nam Co Lake. The roughly water balance analyses of lake water volume implied that, in two study periods (1971–1991 and 1992–2004), the precipitation supplies (direct precipitations on the lake area and stream flow derived from precipitations) accounted for 63% and 61.92% of the whole supplies, while the glacier melting water supplies occupied only 8.55% and 11.48%, respectively. This showed that precipitations were main water supplies of the Nam Co Lake. However, for the reason of lake water increasing, the increased amount from precipitations accounted for 46.67% of total increased water supplies, while the increased amount from glacier melting water reached 52.86% of total increased water supplies. The ratio of lake evaporation and lake volume augment showed that 95.71% of total increased water supplies contributed to the augment of lake volume. Therefore, the increased glacier melting water accounted for about 50.6% of augment of the lake volume, which suggested that the increased glacier melting water was the main reason for the quickly enlargement of the Nam Co lake under the continuous temperature rising.
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| [76] |
Estimation of daily maximum and minimum air temperature using MODIS land surface temperature products [J].https://doi.org/10.1016/j.rse.2012.10.034 URL [本文引用: 1] 摘要
Accurate estimation of spatially distributed air temperature (Ta) is useful for a wide range of disciplines such as hydrology, meteorology and ecology. Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (Ts) products hold the potential to get spatial estimates of land surface temperature at high temporal (daily) and spatial resolution (102km) across the world. In this paper, the possibility of retrieving high-resolution Ta data from MODIS Ts data on both Terra and Aqua satellites was investigated over Xiangride River basin in the north Tibetan Plateau. The results of statistical analysis show that during the night MODIS Ts data on Terra satellite provides a good estimation of daily minimum air temperature with RMSE02=022.9702°C, MAE02=022.3702°C, and r02=020.94, while during the day the difference between Terra MODIS Ts data and daily maximum air temperature is large with RMSE02=027.4502°C, MAE02=026.2102°C, and r02=020.83. In order to improve the accuracy of the estimation of daily maximum air temperature, the temperature-vegetation index (TVX) method was used in this paper. By lowering the threshold for the negative correlation coefficient between NDVI (Normalized Difference Vegetation Index) and Ts to 61020.1, the TVX method was applied to MODIS land products to estimate daily maximum air temperature successfully for the first time. The validation results show that the TVX method has improved the accuracy of daily maximum air temperature significantly with RMSE02=023.7902°C, MAE02=023.0302°C, and r02=020.83. Finally, the diurnal air temperature variation was simulated using a simple sine curve model for the period 21:00–9:0002UCT. The simulation results were in good agreement with observed values with RMSE02=023.4302°C, MAE02=022.5402°C, and r02=020.86. The results of this study show that daily maximum and minimum air temperature can be retrieved effectively from MODIS land surface products through the use of TVX method.
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| [77] |
Improvement and expansion of the Fmask algorithm: Cloud, cloud shadow, and snow detection for Landsats 4-74-7, 8, and Sentinel 2 images [J].https://doi.org/10.1016/j.rse.2014.12.014 URL [本文引用: 1] 摘要
61Cloud, cloud shadow, and snow detection for Landsats 4–8 and simulated Sentinel 2.61This algorithm improves the original Fmask algorithm for Landsats 4–7 images.61A new version developed for Landsat 8 that takes advantage of the new cirrus band.61A prototype algorithm designed for Sentinel 2 that does not have a thermal band.61For cloud detection, the cirrus band is more helpful than the thermal band.
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| [78] |
ICESat's laser measurements of polar ice, atmosphere, ocean, and land [J].https://doi.org/10.1016/S0264-3707(02)00042-X URL [本文引用: 2] 摘要
The Ice, Cloud and Land Elevation Satellite (ICESat) mission will measure changes in elevation of the Greenland and Antarctic ice sheets as part of NASA's Earth Observing System (EOS) of satellites. Time-series of elevation changes will enable determination of the present-day mass balance of the ice sheets, study of associations between observed ice changes and polar climate, and estimation of the present and future contributions of the ice sheets to global sea level rise. Other scientific objectives of ICESat include: global measurements of cloud heights and the vertical structure of clouds and aerosols; precise measurements of land topography and vegetation canopy heights; and measurements of sea ice roughness, sea ice thickness, ocean surface elevations, and surface reflectivity. The Geoscience Laser Altimeter System (GLAS) on ICESat has a 1064 nm laser channel for surface altimetry and dense cloud heights and a 532 nm lidar channel for the vertical distribution of clouds and aerosols. The predicted accuracy for the surface-elevation measurements is 15 cm, averaged over 60 m diameter laser footprints spaced at 172 m along-track. The orbital altitude will be around 600 km at an inclination of 94掳 with a 183-day repeat pattern. The on-board GPS receiver will enable radial orbit determinations to better than 5 cm, and star-trackers will enable footprints to be located to 6 m horizontally. The spacecraft attitude will be controlled to point the laser beam to within卤35 m of reference surface tracks at high latitudes. ICESat is designed to operate for 3鈥5 years and should be followed by successive missions to measure ice changes for at least 15 years.
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