Simulation Of Hydrological Effects Of Climate And Land Use Changes In The Upper Reaches Of Hetian River Based On SWAT Model

In recent years,the study of hydrological cycle and water resources under the global change has become a hot issue in hydrological science.Watershed hydrological model is an important tool to study the hydrological process of rivers and simulate the scenario under the changing environment of runoff.As a typical distributed hydrological model,SWAT model is widely used.Therefore,based on SWAT model,this paper chooses the upper reaches of Hotan River as the research area,carries out hydrological simulation on the upper reaches of Hotan River with the support of GIS technology,verifies the applicability of SWAT model in high altitude mountainous areas,studies the impacts of different climates and changes of land use scenarios on runoff,and provides scientific references for characteristics of runoff changes and rational allocation of water resources of basin.The main conclusions of this paper are as follows:?1?From 1962 to 2015,the precipitation and temperature in the upper reaches of Hotan River showed an increasing trend,and the change rates were 13.26mm/10a?P>0.05?and0.33?/10a?P<0.001?respectively.In terms of season,rising rates of precipitation in summer,spring,winter and autumn are 9.54 mm/10a,3.11 mm/10a,0.82 mm/10a and 0.32 mm/10a respectively.The trend of change in each season did not reach the significant level of P<0.05.However the rate of change in temperature from small to large was 0.27?/10a in summer,0.31?/10a in spring,0.29?/10a in winter and 0.43?/10a in autumn,and showed a significant upward trend?P<0.05?.Change characteristics of temperature and precipitation in Hotan River Basin reflected that the climate in this area had a trend of warming and humidifying.?2?From 1962 to 2015,the upward trend of Yurunkax River and Karakash River in upper reaches of Hotan River was 3.04 m3·s^-1/10a?P>0.05?and 4.03 m3·s^-1/10a?P<0.05?respectively.The Cv values of interannual variations of runoff were 0.23 and 0.21 respectively.Changes of runoff were relatively stable,but the annual distribution was extremely uneven.?3?During 1990-2015,the land use in the upper reaches of Hotan River was mainly unused land?50%?,followed by grassland?24.5%?and waterarea?17.9%?,and the rangeability of land use was becoming smaller and smaller.Types of land usemainly changed from water area to grassland?3100 ha?and unused land?6300 ha?in Yurunkax River Basin from 1990 to 1995.The Karakash River Basin is mainly diverted from grassland to water area?7700 ha?,and the unused land mainly came from grassland?73.3%of the total transferred area?and water area?67.6%?.From 1995 to 2005,the land in Yurunkax River Basin was mainly converted from unused land to grassland?13500 ha?and water area?8000 ha?.Water area of the Karakash River and unused land converted to grassland up to 8700 ha.The water actually transferred to unused land of39200 ha.The land use pattern in the upper reaches of Hotan River changed from grassland and unused land to cultivated land?1200 ha?from 2005 to 2015.?4?SWAT models of Yurunkax River and Karakash River basins were constructed and their monthly runoff processes were simulated.The results show that the Nash coefficient?NS?between the simulated and measured runoff of Yurunkax River is 0.84 and 0.85,the relative error?RE?is 2.55%and 8.71%,and the determination coefficient?R²?is 0.84 and 0.88 respectively.NS is 0.79,R² is 0.8 and RE is 1.06%during the calibration period of the Karakash River Basin.And the Nash coefficient?NS?of the model validation period is 0.76,the determination coefficient?R²?is 0.77,and the relative error?RE?is-8.81%.All of them meet the basic requirements of application of the model,which shows that the model is suitable for the simulation of hydrological processes in the alpine mountain areas of the region.?5?The calibrated SWAT model was used to establish different change scenarios,quantitatively assess the response of climate and hydrologic reflects of changes of land use.The results show that there is a positive correlation between runoff and precipitation and relative humidity in the upper reaches of Hotan River,but a negative correlation between runoff and temperature,sunshine hours and wind speed.Land use changes cause a small change in runoff in the upper reaches of Hotan River.Compared with the base period,climate change was the main factor causing the runoff change of Yurunkax and Karakash Rivers whose contribution rate was more than 85%,while the contribution rate of land use change to runoff change was less than15%from 1991 to 2015.Climate change is also the main reason for the change of water balance factors from 1991 to 2015.