Runoff Simulation Using SWAT Model In The Middle Reaches Of The Da Gu River Basin

The fifth report released by the Intergovernmental Panel on Climate Change(IPCC) pointed out that the climatic change rate is faster than expected and the future human will be faced with more serious climate situation. Therefore it is highly significant for human’s future living and sustainable development including the utilization of water resources to grasp the scientific law of climatic change and the process and change law of the hydrologic cycle within the river basin.The hydrologic model of SWAT(the Soil and Water Assessment Tool) is chosen in this paper. the hydrologic model of SWAT of the Dagu river basin is built based on the software ARCGIS9.3 to simulate the surface runoff of the Dagu river basin. main contents and results of the research are as follows:(1)Fundamental factors such as the local terrain and soil climate in Dagu river are researched through investigation in this paper and attribute database such as the spatial database, the weather database and the soil database of the Dagu river basin is built.(2)The digital evaluation map, the land use map, the soil map, the weather station and meteorological data of the river basin are imported into the SWAT model,the sub-basin and the hydrologic responseunit, land use and soil covering are divided,the meteorological data is imported and editing input file is generated and run, then the hydrologic model of SWAT is preliminarily built.(3)The most sensitive parameters of this model are adjusted and checked by using the software SWATCUP-2012 according to the run-off records that were actually measured between 1986 and 2000 in the south-village hydrologic station and the Zhangjiayuan hydrologic station of Dagu river basin. the results show that the simulation results are good, the determination coefficients(R2) are all higher than 0.8and the Nash efficiency coefficients(NS) are all higher than 0.7, all of which meet the requirement. This shows that the model can accurately simulate the hydrological analogy of the researched area.(4)Based on the findings above, the historical method of inversion is used in this paper to rebulid the SWAT model based on the land use data in 2000, and the SWAT model is also built in three cases of extreme land use / cover by using themethod of extreme land use. The meteorological data between 2001 and 2003 is input the model and the output monthly runoffs are analyzed. The findings show that the simulated runoff volume by using the land use data in 2000 is greater than that by using the land use data in 1986 which is adopted by the model itself. The runoffs produced in the three cases of extreme land use / cover show changes. The increased area of the forest land and cultivated land will reduce the surface runoff and the increased area of grassland will increase the surface runoff.(5)The postulational situational approach widely used in the research on climatic change is employed in this paper to change the meteorological data between2001 and 2003. The temperature is decreased by 1℃ and 2℃ respectively, and increased by 1℃ and 2℃ respectively. The rainfall amount is decreased by 20% and10% respectively, and increased by 10% and 20% respectively. The situational models above are combined pairwise, combined with the situation of unchanged climate totally 25 climate models are built. The findings show that increased temperature will reduce the surface runoff and decreased temperature will increase the surface runoff.The increased rainfall amount will increase the runoff volume and the decreased rainfall amount will reduce the runoff volume. In the situation that the temperature decreases by 2℃ and the rainfall amount increases by 20%, the surface runoff will reach its maximum. In contrast, when the temperature increases by 2℃ and the rainfall amount decreases by 20%, the surface runoff will reach its minimum.In summary, this research provides a appropriate model for the research on runoff of the Dagu river basin. the model can provide multiple simulation results including the prediction of runoff in future hydrologic research on the Dagu river basin The analysis of simulation results of the land use and climate change also provides practical significance for the future sustainable development and appropriate distribution of the water resources in the river basin.