Runoff Simulation And Response To Climate Change In The Upper Reaches Of The HeiHe River Basin Based On SWAT Model

The hydrological model is a tool for the rational allocation of water resources. Itplays an important role during the hydrological regime and agricultural production. Inrecent years, hydrological models have been developed to the stage of a distributedhydrological model, which describe model parameters, the spatial variation of themodel structure and spatial variability of underlying surface and soil moisture. It is aneffective tool to study the hydrological cycle. The soil and water assessmenttool(SWAT) as a representative of the distributed hydrological model has a widerange of applications of runoff simulation, changes in watershed surface conditions,climate change response simulation, pollute transport modeling and so on.There are increasingly serious water shortages because of human unreasonableuse for a long time, leading to a crisis of water cycle. The climate of the northwest isdry and the land is poor and the vegetation is low, where there is an increasing runoffowing to precipitation increasing and glacial ablation, causing landslides, water andsoil loss and other disaters. Therefore, in the trend of global warming, studying runoffvariation of the northwest has implications ans significance on grasping the runoffvaritation to revent disasters, especially in arid and semi arid areas. The Heihe Riverbasin, located in the middle of Hexi Corridor, which is one of the three major rivers inGansu Province and130,000square kilometers. In recent years, there is shrinkingnatural vegetation and serious deterioration of grasslands in the upper reaches ofHeihe River basin especially. The excessive development of the middle reaches ofwater resources lead to environmental degradation of downstream ecosystems andexacerbating water supply and demand.This paper selects the upper reaches of the Heihe River basin as the study areaand uses the distributed hydrological model of SWAT(Soil and Water AssessmentTool), which is developed by the Agricultural Research Center of the United StatesDepartment of Agriculture. On the basis of the collecting basic data of the watershed,we simulate the runoff in the upper reaches of Heihe River in support of GIS and alsosimulate the effect of test to determine the feasibility of the SWAT model in theapplication of this basin, which provide an effective means of simulation, evaluation and analysis of water resources and lay the foundation for further development of thebasin water researches management.(1) Analyzing and processing the basic data needed in the model runs includingLand use data, Meteorogical data and Soil attributed data, which established thedatabase of land use, meteorology and soil properties. We divide the sub-basin andgenerate the network of extract some parameters which related to the topography withhydrology significance. The whole study area was divided into27sub-watersheds,154hydrological response units.(2) We apply the existing data to simulate runoff and then use the measuredrunoff data to calibrate and validate the model, which determine its applicability in thestudy area. Moreover, we need to calibrate the paramatar and analysis the sensitivity.Using measured annual runoff data of1960-2007was calibration and validation. Therelative error Re was5.7%and5.0%, the Nash coefficient Ens was0.81and0.87, thecorrelation coefficient R2was0.89and0.88; using monthly runoff data of1990-2007was calibration and validation.(3) Based on simulation results for SWAT, we extract water balance componentdata, and select the model validation period1999-2007data from the inter-annual andannual variations to analyse. The results are as follows: the precipitation is the mostimportant watershed vapor source, and the rest are spending moisture. Theevaporation is accounting for40%of the output of precipitation. There are basicallythe same trends for precipitation and surface runoff in annual variation, which obtainsthe maximum in July, and the minimum value in December and January. Theremaining component change slightly. There is a negative correlation betweenmonthly soil moisture and monthly precipitation on correlation analysis. However,other components are positively correlated with monthly precipitation and thecorrelation is not so obvious.(4) In the upper reaches of Heihe River basin, the annual runoff, precipitationand evaporation presented an overall increasing trend, with a significant increase ofthe annual precipitation and evaporation. The abrupt change year in the upper reachesis1979by nonparametric Mann-Kendall test and accumulative anomaly. We calculatethe contribution rates of climate change and human activity on the runoff by the change rate of accumulation slope. There is always increasing trend for runoff around1979, and annual precipitation and evaporation have the similiar variation, theircontribution rates to the increase of runoff were42.33%and10.96%, respectively.The contribution is46.71%for human activities on runoff, without considering theimpact of other meteorological elements.(5) Based on the above results, we establish different climate change scenarios toexplore the hydrological response under climate change in the upper reaches of HeiheRiver. The results show that the runoff effect under precipitation change is larger thanthat under temperature change. They also two double impact the runoff at the sametime. The precipitation is a major factor on runoff change in the future.