RS And GIS Based Quantitative Assessment Of Soil And Water Loss In China

Research on soil erosion and environment at regional scale is one of the frontier researchfield of soil erosion science, which mainly includes regional soil erosion factors research,regional soil erosion quantitative assessment, soil erosion and impacts of soil conservation onregional environment and so on. Research on regional soil erosion factors is the basis forunderstanding the characteristics of eroded soil environment and provides parameters for soilerosion quantitative assessment, and is also an important direction of soil erosion andenvironment research.Soil erosion was caused by both natural factors and human factors. Natural factors arethe potential conditions in the development of soil erosion, mainly including rainfall,landform, vegetation, soil and so on, which affect soil erosion in different ways.This studyanalyzed the natural factors including rainfall, soil erodibility, terrain (relief amplitude andground roughness) and vegetation coverage that affected soil erosion in China using remotesensing(RS), geographic information system(GIS) and statistics based on Universal Soil LossEquation(USLE) model, and dynamically analyzed these dynamic factors. Raster database ofnatural factors was created and maps of China’s soil erosion factors (Rainfall erosivity map,soil erodibility map, relief amplitude map, ground roughness map and vegetation coveragemap) were made. The distribution of soil erosion in China was analyzed using slope factorand vegetation coverage (1998-2007) factor, and then the USLE was combined with GIS toquantificationally evaluate the soil and water loss in China and maps of China’s soil erosionclassification map in1998and2007were made. The temporal and spatial dynamic analysis ofsoil erosion were made on the basis of the evaluation maps, which would provide some basicinformation for the comprehensive control of regional soil erosion.The main achievements of this study are as follows:1. The monthly and yearly rainfall erosivity was calculated based on the daily rainfalldata from680ground weather stations in China. The temporal variation characteristics ofrainfall erosivity was analyzed using spatial interpolation by Kriging method, linear tendencyestimation, moving average, accumulated deviation, coefficient of variation (CV), and trendcoefficient (r). Then the overall trend of rainfall erosivity in a long sequence was tested forsignificance using statistical correlation coefficient test, while the spatial distribution features of rainfall and rainfall erosivity were compared and analyzed. The interannual variation ofrainfall erosivity was consistent with the interannual trend of annual rainfall and erosiverainfall, which was unimodal distribution and mainly distributed between April and October.The range of the R of annual rainfall erosivity between1998and2011was22249.32MJ mm/(ha h a), which was decreasing fluctuatingly, and the tendency rate was-278.29MJ mm/(ha h10a). The overall trend of rainfall erosivity did not pass the significanttest with the level of90%, which meant the interannual variation was not significant. From1998to2011, the rainfall erosivity decreased in spring, summer and winter, while the trendwent up in autumn. The tendency rate was between-0.213and0.338from January toDecember and the coefficient of variation of rainfall erosivity in each month was above0.1.The degree of variation of each season in a descending order was as: summer, spring, autumnand winter. The spatial distribution of rainfall and rainfall erosivity gradiently decreased fromsoutheast to northwest. In southern China, it gradiently decreased from the center where thevalue was high to outside.2. The spatial distribution of the chemical and physical properties of soil was analyzedbased on the soil map of China (1:1,000,000). The K value of China’s soil erodibility wascalculated using EPIC model and revised using Zhang Keli’s revised formula and the map ofChina’s soil erodibility was made. The spatial variation of the K value of China’s soilerodibility was small and had significant regional characteristics. The range of the K value ofChina’s soil erodibility was between0.0018and0.089t ha h/(ha MJ mm) and the mean was0.0363t ha h/(ha MJ mm). The K value focused between0.030and0.045t ha h/(ha MJ mm),and the land area with such K value took over half of the study area. The high value of soilerodibility was mainly distributed in parts of the Xinjiang Uygur Autonomous Region, southof Inner Mongolia Plateau, north of Loess Plateau and north of the Qinghai-Tibet Plateau. Insouthern China, the K value was usually lower than average.3. Based on90m×90m SRTM DEM, the relief amplitude of China was extracted usingthe neighborhood statistics analysis method (rectangular neighborhood and circularneighborhood), the neighborhood area and average relief amplitude were carriedlogarithmically fitting and passed statistical tests; the best statistical unit of90m×90m SRTMDEM was calculated by using the mean change-point analysis method, which was the11×11and R=6. Finally, the map of China’s relief amplitude grade was made and the features ofrelief amplitude were analyzed. The relief amplitude in parts of China was large, the wholerelief amplitude was relatively flat, which was mainly medium-sized, followed by micro-sized.The relief amplitude had significant differences in space on the east-west and north-southdirection, the big and great relief amplitudes were clearly concentrated in the west, while the flat, slight and medium relief amplitudes were mainly distributed in the east, and the mediumand big relief amplitude in the south area, and the relief amplitude of the northern part wassmall. The mean change-point analysis method could overcome the subjective factors, whichwas an ideal method to determine the best statistical unit.4. Based on90m×90m SRTM DEM, China’s ground roughness was calculated by theinverse of the cosine of slope. The national ground roughness was between1and31.4296,and the mean value was1.035. Ground roughness had significant differences in the east-westand north-south direction. In western China, along the edge of the Qinghai-Tibet Plateau andTianshan Mountains, ground roughness was great and significantly greater than that of theeastern region, and the ground roughness in north region was mainly small and significantlysmaller than that of the southern region. In the basins and plains region, the ground roughnesswas small, and in the complex terrain such as Tianshan Mountains, Hengduan Mountains andthe Qinling Mountain area, ground roughness was great, this trend was similar to thecharacteristics of the relief amplitude.5. The correlation analysis was made between the relief amplitude (11×11grid unit ofrectangular neighborhood and R=6grid unit of circular neighborhood) and ground roughness.The results showed good correlation, and the circular neighborhood was better thanrectangular neighborhood, so in the national scale, slope and slope factor value was calculatedby the best statistical unit（R=6）of the relief amplitude, the maximum value was20.95, andthe mean value was7.80. The spatial distribution characteristics of slope, relief amplitude andground roughness were basically consistent, and there were significant differences in theeast-west and north-south direction.6. This study applied maximum value composites (MVC), one-dimensional linearregression and differential methods to analyze spatial distribution and inter-annual and annualchanging patterns of vegetation coverage in the whole China and Shaanxi Province based on372images of SPOT-4/VEGETATION (S10) data recorded from April1998to July2008.The vegetation coverage both in the whole China and Shaanxi Province generally raised withfluctuations and its inter-annual variation was basically the same. However, there was obviousseasonal variation within a year that vegetation coverage increased from spring to summerand then decreased from autumn to winter. Vegetation coverage changed significantly invarious regions of Shaanxi. It increased dramatically in Northern Shaanxi, especially in thesoutheast of Yulin city and in the north of Yan’an city. The high vegetation coverage(>60%) inQiaoshan, forest area of Huanglong Mountain and Qinba Mountain increased by10%~20%during the past10years. Vegetation coverage in whole China spatially extended from thenortheast to the southwest and decreased from the southeast to the northwest. Vegetation coverage was high in eastern China and low in the west of the boundary between the semiaridarea and sub-humid area especially and the lowest (about zero value) in the desert zone.7. According to the criteria for soil erosion made by the Ministry of Water Resources（SL190—2007）, the datasets of slope and vegetation coverage were used to conduct qualitativeassessment of soil and water erosion in China and make soil erosion intensity maps(1998-2007). The results showed the spatial distribution patterns and changing trends of soilerosion intensity were generally consistent from1998to2007. Spatially, there weresignificantly differences between eastern China and western China. Among soil erosionintensity types, micro erosion type occupied first place, slight erosion type came second, andmiddle erosion type was the third. Furthermore, this study used USLE model and atlas of soilerosion factors, by means of the raster calculation module of ArcGIS (version9.3), tocalculate soil erosion modulus in1998and2007to obtain the soil erosion intensity gradingmaps of the two years so as to analyze the dynamic changes of soil erosion intensity indifferent erosion areas. There were significantly differences in terms of the largest erosionmodulus and average erosion modulus in each erosion areas. Comparing with the relatedresults in1998, soil erosion intensity generally weakened and the total erosion amountdecreased in2007, except that the largest erosion modulus of mountainous regions in northernChina and average erosion modulus of loess plateau in northwestern China increased.