Hydrological Simulation Based On SWAT In Lasa River Basin

Lhasa City acts as the most important role in political and economic of Tibet, as well as in cultural and religious. It hasgreat significanceto analysis the runoff variation process laws under different rainfall frequency and land use conditions of the Lhasa River Basin, and it is vital to regional water resources utilization andreservoir operation, which can improve ability to resist flood and drought disasters, keeping Tibet autonomous economic and social development and prosperity. Using distributed hydrological model SWAT(soil and water assessment tool) to establish hydrological simulation system in the Lhasa River Basin; simulating runoff changes of the Lhasa River Basin under different conditions by changing the input conditions of meteorological and land use; then finding out the main influence factors of Lhasa River runoff change to provide scientific basis for Lhasa River water resources development, utilization and management.This paper mainly adopts linear regression and other long term trend analysis methods to analyze the historical trends change of the precipitation, temperature and runoff of Lhasa River Basin during the period 1963~2008, and then studies its conspicuousness; secondly, the paper simulates the surface runoff by SWAT(a distributed hydrological model), which proves that the model works well in the research area; finally, the paper also adopts different land use data under different age backgrounds and pseudo different land use conditions by changing the temperature, precipitation, and other climatic conditions to study the change of runoff in the Lhasa River Basin under different scenarios. The main conclusions are as follows:(1) Adopting linear regression method analyze and studythe trend change of thehistorical precipitation, temperature and runoffduring the period of 1963~2008 of Lhasa River basin. The results indicated that: the annual historical temperature and annual historical precipitation all increased significantly druing the period;annual runoff at Lhasa hydrological station also increased, but not significantly.(2) Using the basic data of the Lhasa River basinto build a hydrological model with the help of ArcSWAT, so as to simulate the monthly runoff of the research area. The model simulated monthly runoff process of many years, and the data of 2000 to 2004 was used for calibration, with data 1995 to 1999 and 1999 to 2008 was for validation. The results show that, in the model calibration period and two validation periods, Nash-Sutcliffe efficiency coefficient is 0.83, 0.72 and 0.62 respectively, the relative error of Re is 18%, 31% and 18% respectively, and the correlation coefficient R2 is 0.88, 0.85 and 0.84 respectively; in the period 1995 to 2008, Nash- Ens Sutcliffe efficiency coefficient is 0.75, the relative error of Re is 0.27, the correlation coefficient R2 is 0.87.(3) Comparing the annual runoff under land use/cover scenario of 1980, 1995, 2000 and 2014, with two hypothetical scenarios that assuming all unused land converting into grassland or forest, results are compared, the results showed that land use change had little inpact on river runoff change of Lhasa River. Then, with simulating of 12 climate changing scenarios,which the precipitation and temperature changed by a specified scale respectively, and the two factors both changed, the results showthat there is a positive than th relationship between precipitation and annual runoff change;the higher temperature can reduce runoff, but the impact is relatively weak.