Research Of Runoff Simulation In Chaohe Basin Using SWAT Model

In the background of global warming, world population gradually increasing and human beings increasing their demand of water resources by degrees, regions in North China are faced with an intense contradiction between water resources’supply and its demand.Miyun reservoir is an important earth surface drinking water supplier to Beijing, our capital city. Since the 1980s, soil and water conservation projects like "Three-North" Shelterbelt Construction Project,Miyun Reservoir Upstream Water and Soil Conservation Project and Beijing-Tianjin Sandstorm Source Area Anti-Desertification Project are implemented by the government to prevent soil erosion’s further deterioration in Miyun reservoir upstream basin (Chaohe basin included). Land cover of Chaohe basin changes intensively in recent years, its runoff environment of underlying surface followingly changes. Since the year of 1999, Chaohe basin sufferes a persistent drought climate period and a significant reduction in surface flow. Chaohe watershed area accounts for 30% of Miyun reservoir watershed, while Chaohe river contributes to 60% of Miyun reservoir Basin water storage yearly. Chaohe basin has become the most important catchment area for Miyun reservoir, Chaohe river plays an important role in Miyun reservoir’s water deployment. So, using a scientific means to simulate Chaohe basin’s runoff not only provides a reference for the rational development and a sustainable utilization of water resources for Chaohe basin, but also provides a reference for other watersheds’ water resources management in Haihe river basin. Based on the SWAT2009 software, Harmonized World Soil Database (version 1.1), land use spatial data of the year 2000 and 2010, meteorological data from 1956 to 2013, and monthly runoff data from 2006 to 2011, this paper analyzes the regular pattern of Chaohe basin climate change in the past 60 years and land use change in the past 10 years, constructing an applicable SWAT database for its runoff simulation and forcast. In order to analyze runoff’s response from a specific land use change, this paper sets three extreme land use situations. Conclusions are:(1)Forest land was the dominant land use type in the past 10 years, followed by lawn land and arable land, those land use types accounted for 98% of the study area. In terms of land use spatial distribution, forest land was widely distributed, arable land was banding distributed along the river, unutilized land and construction land were scattered distributed.(2)Precipitation in Chaohe basin was mainly concentrated from June to September, those months’ precipitation accounted for 80% of the whole year. In recent 60 years, the annual average precipitation of Chaohe basin was decreasing at the rate of -1.74mm/a, at the same time, the annual average temperature was increasing at the rate of 0.028℃/a.(3)Based on the digital elevation model data of the study area,29 sub-basins and 194 hydrologic research units are divided and extracted. By using LH-OAT algorithm the SWAT software itself provides, this research calculates three most sensitive parameters, those parameters are Alpha_Bf, Esco and CN2.Then, two mathmatic indices are introduced to evaluate SWAT model simulation’s accuracy. Researches show that in model calibration period(from2006 to 2009), Nash-Sutcliffe efficiency coefficient (Ens) and Pearson correlation coefficient(R2) value of Dage hydrological monitoring station acquire 0.61,0.81respectively, Xiahui hydrological monitoring station’s Ens and R2 acquire 0.74,0.84.In model verification period(from2010 to 2011), Dage hydrological station’s Ens and R2 acquire 0.75,0.82 and Xiahui hydrological station’s Ens and R2 acquire 0.80,0.79. Considering the simulation criteria, a calibrated SWAT hydrological model has a good applicability in the study area.(4)Finally, this paper sets up two climate change situations and three extreme land use situations, researches show that, with the extreme increase of arable land and forest land’s coverage, runoff has a decreasing trend, with the extreme increase of Lawn land’s coverage, runoff has an increasing trend.