ANALYSIS OF RUNOFF RESPONSES TO LAND USE CHANGES BASED ON SWAT MODEL IN CHAOHE WATERSHED OF MIYUN RESERVOIR, NORTH CHINA

As a main tributary of Miyun Reservoir, the most important surface water source in Beijing city, the Chaohe River has been witnessed significant streamflow variations over past five decades. Land use had an important impact on runoff variations. In this paper, the SWAT model was applied to estimate the seasonal average runoff and its dynamic variations in Chaohe watershed under different land use scenarios. The contributions of land use changes were analyzed to clarify the runoff responses to this main influence factors. The results showed the following: (1) the shrub land, grassland, farmland and woodland were the main land use types in the research area. The watershed witnessed runoff reduction due to land use changes. And contributions of land use changes had not apparent relief with the trend of the time series; (2) the runoff reduction was the results of the woodland and farmland area growth, especially the substantial woodland increase; (3) the shrub land and the grassland would increase the runoff, the former provided greater help which increased about 1.58 times of the original runoff; contrarily, the farmland (41.7%) could lessen the runoff more obviously than the woodland (23.7%). It is critical to develop adaptive land use assignment to insure the balance of soil and water conservation and runoff generation in the ecological system. The understanding of the various runoff responses could provide the comprehensive water resource management for the government with theoretical foundation under different scenarios of land use changes.