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    Influence of land use change on surface energy balance and climate:results from SiB2 model simulation
    LIU Fengshan, TAO Fulu, XIAO Dengpan, ZHANG Shuai, WANG Meng, ZHANG He
    PROGRESS IN GEOGRAPHY    2014, 33 (6): 815-824.   DOI: 10.11820/dlkxjz.2014.06.010
    Abstract1031)      PDF (4939KB)(1727)      
    The influence of land use and cover change (LUCC), by means of biogeophysical processes, on surface energy balance and climate is highly concerned by climate scientists. Driven by spatially interpolated meteorological data and remote-sensing derived leaf area index validated by on-site observations, the Simple Biosphere model (SiB2) was used to simulate the surface energy balances for different land use types, i.e. farmland, grassland and forest in northeast China, from 2001 to 2010. The SiB2 model validation was done by comparing simulation results with observed surface energy balance components and temperature in 2003 for the three land use types. The effects of LUCC on surface energy balance and climate was based on the average simulation outcomes in 2001-2010. Biogeophysical parameters (including albedo and roughness length), surface energy balances (net radiation flux, latent heat flux and sensible heat flux) and climate (canopy temperature) were analyzed to demonstrate the influences of LUCC. The results show that: (1) The simulated and observed data have similar annual trends ( R 2>0.42) but there is a gap of ±30 W/m 2 for energy balance components and ±4 ℃ for temperature, based on annual averages. The model imitated the surface energy balance and temperature very well, and was used in the simulation of surface energy balance in northeast China. Sensitivity analysis revealed that the major influencing factor of surface energy partitioning was leaf area index, not vegetation cover as set in the SiB2 model. (2) The impacts of different land use types on surface energy balance and climate through biogeophysical processes were simulated using the same meteorological data for the purpose of eliminating the effects of meteorological conditions. The 10 year averages showed that albedo was lowest in forest, followed by grassland and farmland, while forest > farmland > grassland for leaf area index, forest < grassland < farmland for Bowen Ratio and forest > farmland > grassland for roughness length. (3) Trapped net radiation by ecosystem was primarily determined by albedo. Forest traps the highest net radiation, which is mainly allocated into latent heat flux; farmland traps the lowest net radiation, which is mostly channeled into sensible heat flux, and grassland is in between for both net radiation and its partitioning. (4) Canopy temperature (℃) was determined by the relative importance of albedo and the partitioning of net radiation into latent and sensible heat fluxes: forest (7.7)>farmland (7.64) > grassland (6.67), on annual average. The highest temperature of forest was decided by the lowest albedo, but the higher temperature of farmland as compared to grassland was caused by the higher Bowen ratio of farmland. (5) Precipitation was the predominant impact variable on surface energy balances, and was the main cause of the deviation of SiB2 simulation for forest. With the increment of precipitation in all three land use types, the net radiation flux partitioning into latent heat flux was enhanced, and that into sensible heat flux was weakened, as rain increases soil water content; at the same time, canopy temperature also decreased. The results of this research support the warming effect of farmlands converted from grasslands, which have taken place in northeast China over the past few decades.
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    Cited: CSCD(4)
    Wind erosion in Xilingol League, Inner Mongolia since the 1990s using the Revised Wind Erosion Equation
    GONG Guoli, LIU Jiyuan, SHAO Quanqin
    PROGRESS IN GEOGRAPHY    2014, 33 (6): 825-834.   DOI: 10.11820/dlkxjz.2014.06.011
    Abstract1481)      PDF (16519KB)(5336)      
    Soil wind erosion is a major ecological environment problem in northern China. Xilingol League is located in the arid and semiarid areas. As one of the areas suffering from most serious wind erosion in northern China, its ecological environment is very fragile. Because of this environmental fragility, the area was included in the Beijing-Tianjin Dust Storms Sources Control Project that was officially approved by The State Council and implemented in 2002. In order to better understand the status of soil erosion and guide the regional desertification prevention, it is necessary to assess the variation of soil erosion and reveal the influences of weather and vegetation on soil erosion in Xilingol. In this study, based on wind speed, temperature, precipitation and other meteorology data, the normalized difference vegetation index, snow coverage and other remote sensing data, the Revised Wind Erosion Equation (RWEQ), which takes Newton's first law of motion as the foundation, was applied to evaluate annual soil losses caused by wind erosion. The results show that: The average soil erosion in Xilingol League between 1990 and 2010 was 0.34 billion tons. The intensity of soil wind erosion is low in most parts of Xilingol—these areas were mainly concentrated in the eastern, central and southern areas, where vegetation coverage is higher, wind erosion forces is lower, and rainfall is abundant. The areas with medium and higher intensity of erosion were mainly distributed in the Hunshandac desert of Suninteyou Banner, Zhengxiangbai Banner and Zhenglan Banner, where the soil is highly prone to wind erosion. Since the 1990s, soil erosion in Xilingol showed a deceasing trend. The reduction of wind erosion intensity is related to the weakened wind energy and improved vegetation cover. Wind erosion forces is the main driving factor of wind erosion—soil erosion was significantly correlated with the wind erosion forces ( r=0.95, p<0.05). Wind erosion in Xilingol occurred frequently in windy springs. At this time, the effect of soil erosion associated with low vegetation coverage is most significant. Soil erosion was significantly correlated with the spring vegetation coverage in regions of higher wind erosion forces ( r>0.7, p<0.01). Increased vegetation coverage effectively reduced soil wind erosion of the region in the recent 20 years. Low vegetation coverage makes the prevention of soil erosion more difficult and improving the grassland condition, especially in the spring season, is the key to controlling wind erosion of the soil. The RWEQ model was mainly used in the farmlands of the United States and cannot be directly applied in the grassland areas of China. In order to better apply the model in grasslands, the soil particle content was converted into the US system, surface roughness was measured by the roller chain method and withered vegetation coverage (obtained by photos) was introduced to replace flat residues on the surface of the soil. Even so, more research is needed to solve problems such as the influence of relief on soil wind erosion, the determination of noneroding boundaries, among others.
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    Cited: CSCD(27)
    The extreme cold winter of 1620 in the middle and lower reaches of the Yangtze River
    YAN Junhui, LIU Haolong, ZHENG Jingyun, HAO Zhixin, GE Quansheng, FU Hui
    PROGRESS IN GEOGRAPHY    2014, 33 (6): 835-840.   DOI: 10.11820/dlkxjz.2014.06.012
    Abstract875)      PDF (1846KB)(1237)      
    Climate extremes have become a hot topic in the field of climate change research. In this study, the snow-cover days over the middle and lower reaches of the Yangtze River (MLRYR) in the winter of 1620 were extracted from Chinese historical documents and archives. Using these records, the winter temperature anomalies (with respect to the 1961-1990 mean) of 9 stations were estimated based on the relationship between winter temperature and snow-cover days during the period with available instrumental observations. The regional winter temperature anomaly over the MLRYR was also estimated through stepwise regression. The results show that: (1) The regional mean snow-cover days for the middle and lower reaches of the Yangtze River were about 50 days, with high spatial variability. Snow-cover days ranged from 30 in Shanghai to 100 in Jingzhou, and the average snow-cover days were approximately 70 days in Hefei, Huoshan, Nanjing, Chaohu, among others in the region. Snow-cover days in Anqing, Wuhan, Changde, Changsha and Jingdezhen were 40 to 60, while the least snow-cover days of about 30 were found in Shanghai and southern Jiangsu Province. (2) It was extremely cold in the winter of 1620, and the regional mean winter temperature was estimated to be lower by approximately 4.4℃ than that in the period of 1961-1990. The maximum (coldest) winter temperature anomaly occurred in Jingdezhen, with winter temperature anomaly of about 5.7℃ lower than the reference period. The next were Huoshan, Hefei, Changde,Wuhan and Shanghai, with the winter temperature anomalies ranging between -5 and -4℃. Nanjing, Anqing and Changsha experienced smaller negative anomalies, ranging from -4 to -3℃. The minimum (warmest) winter temperature anomaly was detected in Changsha, but it was still much lower than the coldest record during the observational period.
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    Cited: CSCD(3)
    Research progresses on the interaction between desertification and climate change in arid and semiarid East Asia
    HUATing, WANG Xunming
    PROGRESS IN GEOGRAPHY    2014, 33 (6): 841-852.   DOI: 10.11820/dlkxjz.2014.06.013
    Abstract1227)      PDF (5212KB)(1852)      
    Interactions between climate change and land surface processes, especially in arid and semiarid areas, have received increasing attention in recent years from climate scientists and geographers globally. In this paper, progresses in existing research on the interaction between desertification and the climate system in arid, semiarid, and semi-humid East Asia are outlined and discussed. Although there are large regional differences, the climate system affects regional desertification process by altering temperature, precipitation, wind field, and other meteorological factors. The current findings indicate that precipitation has a relative explicit impact on desertification: increases in precipitation are beneficial for vegetation growth and the reversal of desertification, and decreases in precipitation may result in increased desertification. Comparatively, the influences of temperature and wind field on desertification are more complicated and differ among various subregions: in the eastern monsoonal area, rises in temperature and the upper dominant southwest wind may be accompanied by increases in precipitation, contributing to reversals of desertification; in the western non-monsoonal area, rises in temperature promote increases in both surface evaporation and river runoff as a result of enhanced glacier thawing and snow melting, thus it is uncertain how this temperature change affects desertification; in the higher latitudes and altitudes, droughts and frost disasters often act together and give rise to severe damages to regional ecosystem, triggering increased desertification. On the other hand, desertification to some extent affects the local climate system by altering the characteristics of vegetation, land surface and soil. Increased desertification leads to vegetation degradation and subsequently changes in surface albedo, latent heat flux, as well as surface roughness height, which may in turn alter temperature, probabilities of precipitation events, and the wind regimes of local areas. Desertification also leads to the release of higher amount of fine particulates into the atmosphere, which may negatively affect the occurrence of precipitation. Overall, the interactions between desertification and the climate system include many feedbacks, among which the positive albedo-temperature-vegetation feedback and the positive sand-dust-precipitation-vegetation feedback are the principal mechanisms. Despite considerable progresses made in existing research, however, there remain many important issues that are yet to be addressed or difficult to address, such as the spatial and temporal aspects of processes involved in desertification, which are critical for understanding the interactions between climate change and desertification, and thus further studies are needed in the future.
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    Cited: CSCD(6)
    Progress of research on forest land cover change in the Indo-China Peninsula
    LIAO Chenhua, FENG Zhiming, LI Peng, ZHANG Jinghua
    PROGRESS IN GEOGRAPHY    2014, 33 (6): 853-864.   DOI: 10.11820/dlkxjz.2014.06.014
    Abstract1309)      PDF (554KB)(1375)      
    Forest cover is an extremely important natural resource in the Indo-china peninsula. It is of significant importance to the local ecological environment and socioeconomic development. This paper systematically summarizes and reviews research progresses on forest cover change in the Indo-china peninsula with respect to remote sensing monitoring and mapping, spatial-temporal variations, driving forces and ecological environmental effects, and discusses existing problems in these researches and trends of development. The results show that: (1) forest cover monitoring in the Indo-China peninsula have changed from optical remote sensing to radar remote sensing, and monitoring methods from single to multiple classifiers and data sources. The monitoring objects were mainly on natural forest covers, while monitoring of planted forests still face many difficulties; (2) forest cover area increased from 1980 to 1990 and declined since 1990. Among the five member countries of the Indo-China Peninsula, Thailand, Laos, Myanmar and Cambodia had decreased forest cover after 1990, while Vietnam is the only country where forest transition has occurred after the 1990s. The regional differences of forest cover change were significant in the Indo-China peninsula; (3) direct driving factors of forest cover changes were mainly cash plantation expansion, slash-and-burn cultivation, road construction and commercial logging, while indirect driving factors mainly included population change and socioeconomic and policy factors. The impacts on forest cover change were reflected in forest cover area, forest degradation/regeneration, and forest landscape ecology. The extent of impact was directly related to the pattern, intensity and frequency of disturbances; (4) the ecological and environmental impacts of forest cover change were mainly on water, atmosphere, soil and biology. Impact on water is focused on water retention of canopy and soil moisture regulating. Impact on the atmosphere is mainly on greenhouse gas emission and regional climate change. Impact on soil is largely on soil carbon emission and soil erosion. Biological impact is primarily on biodiversity. The forest cover change research in Indo-China peninsula has the following problems: (1) forest cover remote sensing monitoring was mainly on global area of forest cover, while studies on different forest types were rare, especially on local typical plantations. Research on forest degradation and regeneration was also inadequate; (2) the research of spatiotemporal patterns of forest cover change was mainly large-scale, while small-scale studies, especially comparative study of different countries or regions, were fewer; (3) research on the driving mechanisms of forest cover change was mostly qualitative or semi-quantitative, while integration of various data and quantitative analysis were inadequate. In view of these problems, future research on forest cover change of the Indo-China peninsula could be strengthened in the following three areas: (1) to explore or improve the monitoring methods of forest cover change, especially forest cover change in typical regions or typical forest types; (2) to enhance multi-scale, comprehensive and comparative study of forest cover change in the Indo-China peninsula; (3) to enhance quantitative study of forest cover change and the driving mechanisms.
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    Cited: CSCD(1)