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  • Original Articles
    Progresses of palaeochannel studies in China in the past 20 years
    ZHAO Yanxia, XU Quanhong, LIU Fangyuan, QIN Yanjie, WU Chen, CHEN Lijiang, CUI Junhui
    2013, 32(1): 3-19. https://doi.org/10.11820/dlkxjz.2013.01.001
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    The last 20 years have seen new progresses in palaeochannel studies in China, including the investigations on palaeochannels in Nenjiang Daan, palaeochannels in the plain south of Laizhou bay, and palaeochannels, deep ancient grooves and submarine palaeochannels in the Yangtze river downstream of Nanjing, and so on. As a result, a large number of achievements have been accomplished, and new theories proposed; the research achievements have found new applications as well. The new knowledge and new theories indicate that buried palaeochannels exist in all of large outflowing rivers in China since the LGM(Last Glacial Maximum). The palaeochannel runs deep into the stadial terrestrial and the sea bed of the continental shelf from the Last Glacial Epoch, forming a cutting valley with deep grooves at the bottom, stacked with fluvial carryover and coarse particulate material from the LGM and early Holocene. The upper part of the valley is covered with marine, paralic, and continental fine-grained material from the Holocene, which frames the shallow-buried palaeochannel with 20 m to 50 m depth. Palaeochannels are rich in underground water, and an important water source for the areas of alluvial plain and shallow continental shelf.
  • Original Articles
    Research progress on the time series analysis methods in hydrology
    SANG Yanfang, WANG Zhonggen, LIU Changming
    2013, 32(1): 20-30. https://doi.org/10.11820/dlkxjz.2013.01.002
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    Hydrological time series are usually composed of various components with complicated characteristics.At present it is generally thought that hydrological time series mainly show stochastic,fuzzy,nonlinear, non-stationary,and multi-temporal scale characteristics.In this paper,research progresses on the time series analysis methods to study the characteristics of hydrological processes and their applications are summarized,including serial correlation analysis methods,hydrological frequency analysis methods,fuzzy analysis methods,chaos theories and methods,information entropy theories,and wavelet analysis methods.The main issues and the problems to be solved with regard to the methods mentioned above are discussed,namely,the disadvantages and limitations in their applications to hydrological time series analysis.Finally,it is pointed out that further improvement and optimization of the methods,combination and coupling between the methods,emphasis on the combination of the analyses of physical mechanisms and mathematical statistics,are the key not only to improving the results of hydrological time series analysis,but also to studying and solving the hydrology and water resources issues caused by environmental change.
  • Original Articles
    Advances in digital watershed features extracting based on DEM
    SONG Xiaomeng, ZHANG Jianyun, ZHAN Chesheng, LIU Jiufu
    2013, 32(1): 31-40. https://doi.org/10.11820/dlkxjz.2013.01.003
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    Digital elevation models(DEMs) can be considered as a digital representation of landscape topographic properties. Construction of a DEM-based digital model for a drainage network and extraction of hydrological attributes of the drainage network are important premises for simulation of distributed hydrological processes in a catchment. Usually, the quality and efficiency of the extraction of hydrological characteristics of a river basin from DEM data are affected by treatment of the closed depressions and flat areas in DEM, determination of flow directions, and selection DEM resolutions. In this paper, fundamental principles, methods and algorithms for extraction of the features of drainage networks and watersheds are reviewed; research progresses on the methods for treatment of flat areas and depressions and for determination of flow directions are discussed; the progress on software design and development for extractions from different types of DEM data are introduced; the effects of different scales and resolutions of DEM on the extraction of drainage network and watershed features are explored. Furthermore, the research progresses on the extraction of the features of drainage networks in flat areas and plain region are summarized.
  • Original Articles
    FUTURES: A new regional urban growth simulation model
    DENG Jing, TANG Wenwu, LIU Runrun, ZHENG Xinqi
    2013, 32(1): 41-48. https://doi.org/10.11820/dlkxjz.2013.01.004
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    It is a critical scientific challenge to better simulate urban growth, especially for the regions undergoing rapid urbanization in developing countries. Conventional methods based on single or integrated models, however, can not provide direct support for decision-making. This paper introduces a new urban growth simulation model——FUTURES(FUTure Urban-Regional Environment Simulation). The model was developed by UNC Charlotte Center for Applied GIScience (CAGIS). FUTURES not only considers the gradient calculation of dynamic suitability for urban growth, analysis of the trend of per capita land consumption, and visual simulation of patch changes based on spatial locations, but also focuses on the feedback process of dynamic interactions between modules, thus forms a unique insightful coupling mechanism, and model structure is compact and flexible. A number of experiments have been executed in a high performance computing environment for several study areas of North Carolina, USA. This paper mainly describes the model design, model composition, and key modeling methods, and summarizes the characteristics and advantages of this model. This review provides a reference for urban growth simulation research in China, which will be meaningful and helpful for promoting related research from another point of view.
  • Original Articles
    Surface modeling of seasonal mean precipitation in China during 1951-2010
    ZHAO Na, YUE Tianxiang, WANG Chenliang
    2013, 32(1): 49-58. https://doi.org/10.11820/dlkxjz.2013.01.005
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    The demand for spatial data sets of precipitation in digital form has risen dramatically in recent years. This paper describes a new surface modeling method, high accuracy and high speed method(HASM), which has been successfully used for digital elevation model(DEM) construction and ecosystem changes. We explored the relationship between precipitation and geographical/topographical variables and local topographical factors, developed a polynomial regression model for seasonal precipitation in each region, and then used symmetric successive over-relaxation method and preconditioned conjugate gradient method to solve the matrix equations produced by HASM, which effectively improved the model. We used ArcGIS to create buffers with a specific distance around each subarea, and the actual computational domain expanded to the buffer area. Polynomial regression and residuals interpolation using HASM were applied to develop a gridded precipitation database for China in seasonal scales with a resolution of 1 km in longitude and latitude. We used precipitation data measured at 711 stations during the period of 1951-2010, with 80% of them used for surface development and 20% reserved for validation tests. Accuracy tests revealed that HASM is superior to the classical methods such as Kriging, Inverse Distance Weighting (IDW) and Spline. Precipitation surfaces generated by HASM showed good performance in precipitation research. Therefore, HASM can be considered as an alternative and accurate method for precipitation interpolation in China.
  • Original Articles
    Runoff simulation of climate change scenarios based on HIMS model in the Huangshui river basin
    ZHANG Yanjiao, GAO Xiaohong, LI Qijiang, CHEN Qiang, YANG Junjun
    2013, 32(1): 59-67. https://doi.org/10.11820/dlkxjz.2013.01.006
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    It is important for rational water use and water management to study the change of runoff processes in response to climate change. Based on HIMS(Hydro-Informatic Modeling System) model, using daily precipitation data from 33 rainfall stations from 1986 to 2000, and daily maximum and minimum temperature measured at 8 meteorological stations, this paper presents a simulation of runoff processes in the Huangshui river basin in Qinghai province. Parameter sensitivity analysis and validation of the simulation are conducted using the recorded runoff data from six hydrological stations during the same time period. Results indicate that efficiency coefficient and correlation coefficient of the simulated daily data at five stations exceed 0.5, except Shiyazhuang station; the efficiency coefficient and correlation coefficient of the simulated monthly data at five stations exceed 0.9. Daily and monthly sensitivity analysis and validation generates good outcome as well, demonstrating that the HIMS model applies to the runoff processes in the Huangshui River basin very well, and can be used to simulate the scenarios of areal responses to climate change, which meets the requirements of water resources management. Based on this, the changes of precipitation and temperature in recent 50 years(from 1961 to 2010) in the Huangshui River basin are analyzed, and the hydrological responses(runoff) to 9 types of possible climate change scenarios are simulated and analyzed. The results suggest that climate change has significantly effects on the runoff of the Huangshui River basin. If temperature rises and precipitation decreases, then runoff shows a strong tendency to decrease; on the contrary, if changes of temperature and precipitation reverse, runoff shows a tendency to increase. In addition, in the Huangshui river basin, precipitation is the key climatic factor, and the effect of precipitation change on runoff processes is significantly greater than that of temperature change.
  • Original Articles
    Temporal and spatial pattern of water storage changes over the Yangtz river basin during 2002-2010 based on GRACE satellite data
    XU Min, YE Baisheng, ZHAO Qiudong
    2013, 32(1): 68-77. https://doi.org/10.11820/dlkxjz.2013.01.007
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    The large-scale change of the amount of water storage over the Yangtze River basin is obtained by using monthly gravity field data, derived from GRACE satellite data between April of 2002 and December of 2010 with Gaussian filter. The temporal and spatial variations of water storage over the Yangtze River basin are compared to the data from GLDAS (Global Land Data Assimilation System) model. The results indicate that: (1) The two sets of data, derived from GRACE satellite and GLDAS model, show the same trend of change in the majority of the areas with high level of consistency; the correlation coefficient is 0.89 (P<0.05). (2) The amount of water storage over the Yangtze River Basin from 2002 to 2010 has an increasing trend. The average annual growth rate is 0.43cm/month, equivalent to 95.04×109 m3/a, with an average annual growth rate of 0.53 cm/month (67.13×109 m3/a) in the upstream area, 0.51cm/month (25.73×109 m3/a) in the midstream area, and 0.36 cm/month (9.14×109 m3/a) in the downstream area. The increasing amount of water storage over the Yangtze River Basin during the time period of nearly nine years is estimated to be 855.33×109 m3/a. Judging from the spatial distribution of average annual water storage over the Yangtze River Basin, there is a shortage in January, February, March, and December, and a surplus in July, August, and September, with a clear transition from shortage to surplus in April, May and June from downstream to upstream, and a transition from surplus to shortage in October and November from upstream to downstream. The maximum increase rate of water storage over the whole basin, in the upstream and midstream areas is in September, with 1.01 cm/a, 1.37 cm/a, and 1.05 cm/a, respectively, whereas in the downstream area the maximum increase rate is in July, with 1.62 cm/a.
  • Original Articles
    Improved soil moisture retrieval model from remotely sensed microwave data
    ZHANG Xianfeng, ZHAO Jiepeng, LIU Yu
    2013, 32(1): 78-86. https://doi.org/10.11820/dlkxjz.2013.01.008
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    Retrieving land surface soil water content from remotely sensed passive microwave data has a good physical basis. Thus, it can provide dynamic monitoring of large-range soil moisture condition. The Advanced Microwave Scanning Radiometer for EOS (AMSR-E) data were used to derive soil moisture base value and daily variation for each image pixel, respectively, to build an inversion model for retrieving soil moisture information. A precipitation impact factor was proposed and incorporated into the modeling process to improve the accuracy of soil moisture retrieval. The IDL language was used to implement the proposed model as software modules of the System of Xinjiang Soil Moisture Inversion from Remotely Sensed Data. The in-situ measured soil moisture data by the WatchDog 2400 instrument and Loss-on-Drying method were used to derive empirical parameters for the regressive model that are suited to the conditions in Xinjiang, and to verify the proposed model output. The results show that, with reference to the data of in-situ measurements, our improved model can achieve better estimation of Xinxiang's soil moisture than the soil moisture products of US National Snow & Ice Data Center (NSIDC). The RMSE is improved from 8.4% to 4.25%. The software modules developed in this study can provide a tool for quick soil moisture monitoring in a large area such as Xinjiang.
  • Original Articles
    Characteristics and influencing factors of runoff consumption in the midstream of Shiyang river
    LIU Haimeng, SHI Peiji, ZHOU Junju, LIU Hailong, SUN Huihui
    2013, 32(1): 87-94. https://doi.org/10.11820/dlkxjz.2013.01.009
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    The runoff of some rivers in the world, especially in the arid and semi-arid regions, has decreased remarkably with climate change and intensive human activities of the development of society and economy. This paper analyzes the characteristics of annual mountainous runoff and runoff consumption in the midstream of Shiyang river in the past 50 years. Using Fisher classification method and relativistic consumption rate, a major inflection point has been identified to be the year of 1975, during which human activities started to have significant influences on runoff consumption in the midstream of Shiyang river. The inflection point is clarified to be a point of significant change of runoff consumption caused by human activities, as opposed to the change of natural runoff, which is an improvement to the current research. Based on the types of human activities and the strength of the influences, the trend of runoff consumption in more than 50 years is divided into four stages; the contributions of human activities and natural changes o the influences on the runoff consumption in each stage from 1956-2009 are analyzed quantitatively and qualitatively. The results indicate that, generally speaking, prior to 2000 the contribution of human activities gradually increases; the contribution of natural changes decreases. Natural contribution is significantly correlated with mountainous runoff. Since mid-1970s, the contribution of human activities on the runoff consumption has increased significantly in the midstream of Shiyang river. In 1990s the influences of human activities and natural changes on the runoff consumption reach an equal level. Quantitatively speaking, from 1956 to 1999, the contribution of human activities is equivalent to 0.633 billion m3/a, with 62.31% of water from upstream as directly artificial water consumption, accounting for 71.52% of overall results. After that, the contribution of human activities started to gradually decrease, indicating the sign of relief of the conflicts between water conservation and human activities in the midstream of Shiyang river.
  • Original Articles
    Surface humidity index and the impacting climatic factors in Hedong region of Gansu province
    ZHAO Yifei, ZHANG Bo, ZHANG Duoyong, ZHANG Jianxiang, HE Xuqiang, SUN Liwei
    2013, 32(1): 95-104. https://doi.org/10.11820/dlkxjz.2013.01.010
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    Based on the climatic factors, such as daily maximum temperature, minimum temperature, precipitation, relative humidity, wind speed and sunshine duration, measured daily at 13 stations from 1960-2010 in Hedong region of Gansu province, potential evaporation is calculated for the region using the UN Food and Agriculture Organization(FAO) Penman-Monteith model, which allows the calculation of the surface humidity index for the location of each station. The characteristics of spatial-temporal variations of the humidity index are then analyzed by using the linear regression, Morlet wavelet, Empirical Orthogonal Function(EOF) and Inverse Distance Weighted(IDW) methods, and the climatic factors impacting the surface humidity index are investigated. The results indicate that the study region was wetter before 1992, and the humidity index has been in a downward trend since 1960s, with an interannual decreasing rate of 0.02/10a in the last 51 years and a correlation coefficient of 0.2946(P<0.05). With the exception of slight increase in winter season, the humidity index decreased in other three seasons. The spatial pattern of the change of humidity index of the study region showed clear difference between the south and the north, with the humidity index decreasing from south to north. The abnormal spatial pattern resides in two aspects: the uniformity of the whole area, and the opposite changes in the south and the north. In the meantime, the periods of 19a, 5a and 11a also existed for interannual changes of the humidity index, with the turning point from wet to dry in the year of 1994. Furthermore, in the past 51 years, the climatic factors showed different impacts on the humidity index change in different seasons; the humidity index had positive correlations with precipitation and relative humidity, but negative correlations with sunshine duration, potential evaporation, wind speed and maximum temperature.
  • Original Articles
    The hydrologic-environmental effects of dams and sluices and the assessment frameworks
    ZHANG Yongyong, XIA Jun, ZHAI Xiaoyan
    2013, 32(1): 105-113. https://doi.org/10.11820/dlkxjz.2013.01.011
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    How to resolve the conflicting relationship between basin development and the protection of ecological environment, and to provide an objective assessment of the effects of dams and sluices on the environment, have become one of pressing scientific challenges and a new task of great significance. From the perspective of the natural characteristics of rivers, this paper explores the theories, key topics, and methodologies for the analysis of hydrological and environmental effects of dams and sluices, i.e., quantity and quality of waters, and proposes a quantitative framework to study and simulate water cycle at the river basin scale. As a case study in Huai river basin, one of the areas with most water projects and most polluted water, this paper presents a preliminary analysis of the effects of dams and sluices on the hydrological environment of the area. This study provides a theoretical basis for the management of water resources and control of water pollutions in the areas of dam-sluice regulated river basins, and contributes to the strategies for comprehensive management of river basins and for sustainable socio-economical development of the country.
  • Original Articles
    Accelerating polygon overlay analysis by GPU
    ZHAO Sisi, ZHOU Chenghu
    2013, 32(1): 114-120. https://doi.org/10.11820/dlkxjz.2013.01.012
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    Overlay analysis is one of the most important analysis capabilities of geographic information systems. Overlay analysis with polygon layers is a time-intensive process. To improve time efficiency, modern approaches of overlay analysis are generally divided into two stages, filtering and refinement (also known as polygon clipping). A great deal of effort has been taken to significantly reduce the number of candidates in the first stage (filtering) in order to alleviate the workload of the second stage (refinement). However, the second stage is still the most time-consuming part of the process. In this paper we applied GPGPU (General-purpose Graphics Processing Unit) computing to the two key stages of overlay analysis: MBR filtering (part of the filtering) and polygon clipping, and restricted the search area to polygon intersection analysis. We proposed GPU-based MBR filtering algorithm by combining histogram and parallel prefix-sum algorithms, and introduced GPU-based polygon clipping algorithm by improving Weiler-Atherton algorithm. There are two differences between our algorithm and Weiler-Atherton algorithm: First, it adopts a new method to insert intersecting points which reduces computing workload, making it more suitable to be implemented on GPU. Second, it simplifies the algorithm used to mark entry and exit points. Furthermore, based on dynamic programming, we provided a solution to avoid load imbalance caused by spatial data skew. The improved algorithms and the solution have been applied to filtering stage and refinement stage to achieve better performance. The experimental results show that the speedup ratio between GPU-based MBR filtering implementation and CPU implementation is 3.8. The GPU-based polygon clipping implementation runs 3.4 times faster than the CPU's. Overall, GPU-accelerated polygon intersection implementation achieves performance that is up to three times faster than CPU implementation. Accelerating other types of overlay analyses, such as union, difference, etc., by GPU needs to be studied and implemented in the future.
  • Original Articles
    DEM-based topographic unit diversity index and its algorithm
    TIAN Ruiyun, WANG Yukuan, FU Bin, LIU Yuan
    2013, 32(1): 121-129. https://doi.org/10.11820/dlkxjz.2013.01.013
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    In this paper, based on review of the studies on methods and techniques of terrain information description, topographic unit diversity index (TUDI), a new concept and quantification method, was proposed. The diversity index integrates several terrain parameters, e.g., elevation, slope, slope position, slope aspect, water confluences and distributions information. By combining the algorithms of the topographic position index and the topographic wetness index, using layer overlay analysis method and appropriate indicators for classification and grading, TUDI algorithm re-classifies the types of topographic units, and then calculate the TUDI using the neighborhood statistics and analysis method. The results of the experiment in Sichuan Province as a test region using DEM (100 m×100 m) and waters distribution data (1:250,000, 2005) show that TUDI is a comprehensive index, revealing the complexity and variations of the true surface. In the process of calculation, the topographic units were divided into 13 different types. The topographic unit diversity index was calculated with the statistics window radius set to 900m based on division results of the topographic units. The areas with diversity index value less than 0.5 cover around 11 percent of the whole region; the areas with the value more than 0.75 take up as much as 57 percent. Basically the results of the calculation agree with the topographic features of the study areas. In addition to the experiment to test the reliability of the algorithm, the advantages and disadvantages of it were also evaluated. This research provides a good basis for constructing a conceptual system of DEM-based topographic attributes, as well as for the spatial analysis of terrain information from micro to macro scales.
  • Original Articles
    Conceptual model of disaster chain risk assessment: Taking Wenchuan Earthquake on 12 May 2008 as a case
    ZHANG Weixing, ZHOU Hongjian
    2013, 32(1): 130-144. https://doi.org/10.11820/dlkxjz.2013.01.014
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    A vast number of cases have demonstrated that a major disaster can trigger a series of secondary disasters, forming a disaster chain with much more destructive power than a single-type disaster. Understanding the process of disaster chain formation and establishing a conceptual model for risk assessment are the premise for governance of the disaster chain risk. In this paper, we first reviewed the chain risk assessment models from the studies at home and abroad, e.g., the accident chain, supply chain and so on, and then, taking Wenchuan Earthquake as a case study, we proposed a new conceptual model of disaster chain risk assessment. The two major conclusions are: (1) sensitivity of the environment susceptible to disasters is an important impact factor, which determines the probability of disaster chain. Therefore, the key aspect of risk assessment is to identify the factors affecting the sensitivity of the environment and characterize their quantitative relationships. (2) Vulnerability of a disaster-affected area in a disaster chain increases after incurring repeated hazards; evaluation of change of the vulnerability of the area will improve the precision of disaster chain risk assessment. This study aims to improve the theory on disaster system research and provide a basis for further improvement of disaster chain risk governance.