| With the rapid development of modern science and technology, the application of information technology taking computer and communications as its core widely in hydrology, water resources science and hydraulic engineering science has promoted the research of watershed hydrological model. Now distributed watershed hydrological model has become a focus of hydrology research. The reason was that: on the one hand the model is able to describe spatial variation of precipitation, model parameters, model structure, land surface and soil moisture, etc. On the other hand, practical application of the model is difficult because of mass data, very high accuracy and parameter determination. Huangshui River basin is major water source area of Longkou, Qixia, Zhaoyuan, Penglai in Yantai, deep understanding and effective prediction of regime variation of hydrology and water resources in the study area are not only important aspects of water resources scheduling management, but also have important significance for water resources planning and ecological control and protection. In the paper, SWAT model which was exploited by United States agricultural research center was used to simulate runoff process of Huangshui River basin and discuss hydrological response to environmental changes by joint Chinese-German technical project (2007DFB70200) and Shandong provincial natural science foundation (Y2008E10) . Main research contents and results are as follows:(1)Based on former research accomplishment,the paper synthesized the theories and methodology of disrtibuted hydrological model,including the methods of how to obtain the watershed parameters and route the hydrological process based on GIS, introduction of the hydrological cycle theory, weather simulation theory, structure and application of SWAT. At watershed scale, SWAT was mostly used in the research of river with the basin area of above 1500km2. The applicability of SWAT model when it's used in the research of the river with the basin area of below 1500km2, which also has a reservoir, should be further examined. The research on hydrological response to forest and grassland changes were far more than that to construction land and agricultural land changes.(2)After collecting and processing data, DEM, Land use database, soil database, weather database of Huangshui River basin were built based on ArcGIS. Land use database and soil database separately consist of spatial database and attribute database.(3)Using ArcSWAT, the output data model of Huangshui River basin hydrological simulation was built to simulate 2001-2005 monthly hydrograph. The area of Huangshui River basin extracted from DEM was 941.33km2 and the whole study area was divided into 35 sub-watersheds, 344 hydrological response units. The results reflected that correlation coefficient R 2 was 0.985, 0.792, 0.897, 0.921, 0.892 and Nash coefficient Ens was 0.97, 0.69, 0.85, 0.82, 0.76, indicating the good precision.(4)The paper discussed the runoff response to land use and climate changes,and simulated hydrological process based on hypothesis scenarios using calibrated model. The results were as follows: the runoff effect under temperature change was slighter than that under precipitation change. The runoff increased with the increasing of precipitation but decreased with the increasing of temperature. Annual average runoff depth decreased in the situation of beach, water surface transformed into cropland, construction land and cultivated land, garden plot nearby urban, rural residential area transformed into construction land. The simulation results of conversion of cropland to forest and grassland were: the water holding effects of grass planting was affected by slope and the lower slope limit was, the better the water holding effects were. When the slope was same, the water holding effects of conversion of cropland to grassland was better than that to forest.
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