Spatial-temporal Change Of Runoff And Sediment Discharge Of China

The construction of a prediction model for regional soil and water loss requires research of runoff and suspended sediment discharge factors. Based on hydrological data collected from nationwide hydrological stations, the spatial-temporal change of runoff and sediment discharge of China has been systematically studied in multi-temporal scales (including long-term average, decadal and annual) by validating the runoff and sediment balance, and using computer-assistant cartography and overlay analysis methods of GIS. The main results are as follows.1. Chinese Hydrological Calculation Polygon has been mapped based on existing thematic digital map of China, including a river map, a geomorphology map and a topographic map. According to matter balance theory, the runoff and' sediment accumulative relationship was recorded and the runoff and sediment data integrated from Chinese hydrological control sites. In this way a spatial hydrological database has been established that can provide basic data and unified calculation unit for temporal and spatial change analysis of runoff and sediment discharge.2. Based on matter balance theory and the runoff and sediment accumulation relationship between upper and middle reaches of watersheds, runoff and sediment discharge moduli were calculated using the Visual FoxPro program. Based on these data, a total of 12 time series contour and grid maps of the moduli of runoff and sediment discharge have been mapped at three time-scales, These data have been transformed from point to polygon, and the trend surface of these moduli has been built. This surface provides the data basis for the analysis of spatial-temporal runoff and sediment discharge change and the construction of regional soil and water loss models. According to these maps, the average sediment yield of China is about 3.3 billion tons per year and total runoff is about 32000 m3.3. Using spatial statistics, map algebra algorithms and GIS spatial analysis, the area proportion, sediment discharge proportion and area-sediment discharge relations were analyzed for different sediment discharge moduli grades, and the spatial-temporal change of sediment discharge on two time-scales (decadal and annual) was also studied. The results show the following. (1) Sediment discharge is obviously differentiated at regional scales. Mountainous regions in northern Hebei and western Liaoning, Yanbei Plateau, Loess Plateau, hills in the middle of Sichuan, South-West Plateau and hills south of Huihe are marked with serious erosion and high sediment discharge, while hills in southern of China and small hills in the north-east have little sediment discharge. The northern China Plain, middle and lower reaches of the Yangtze River Plain and the Hetao Plain are sediment deposition regions, whose area account for ten percent of the total area of China. (2) For the whole of China, sediment comes mainly from seriously eroded regions (where the sediment discharge modulus is more than 15000 t/km2.a); fifty percent of the national sediment yield comes fromonly three percent of the total area of China. (3) Over the long term, sediment discharge moduli and all sediment discharge yields decreased between the 1950's and 1980's.4. A set-of methods is proposed for calculation and analysis of runoff and sediment discharge data. The methods include the mapping of hydrological calculation polygons, the analysis of the matter accumulative relationship, construction of a database for hydrological calculation-polygons, the conversion of hydrological data from point to polygon, the mapping of contour and grid maps of runoff and sediment discharge and the dynamic analysis of the temporal-spatial differentiation of runoff and sediment discharge.