Attribution Analysis Of Runoff Change In Min-tuo River Basin

Minjiang River and Tuojiang River are two main water systems in Sichuan Province.Because Minjiang River system diverts part of water into Tuojiang River in Dujiangyan and the two rivers are connected with each other,it is known as"twin River".However,in recent years,the water resources of the big Minjiang River Basin have decreased sharply,and the water resources that can be controlled are facing shortage.Tuojiang River Basin is located in an important population and industrial agglomeration area in Sichuan Province,and in a water shortage area.It needs to draw water from Minjiang River,and there is a contradiction between supply and demand.Min-Ttuo River Basin is an organic and indivisible whole.It is of great significance to study the Min-Tuo River Basin,the most important water system in Sichuan Province,for the water security and sustainable development of Sichuan people.Taking Min-Tuo River Basin as a whole,it is divided into four sub-basins:Dadu River Basin,Qingyi River Basin,Minjiang River Basin and Tuojiang River Basin.The four sub-basins are further divided into 89 second-level sub-basins by using SWAT model.Taking these sub-basins as the research object,the annual precipitation,annual potential evapotranspiration,annual actual evapotranspiration,monthly precipitation,monthly potential evapotranspiration and monthly actual evapotranspiration data from 1981 to 2014 are statistically analyzed.Based on the daily meteorological data of 12 meteorological stations from 1981 to 2014 and the measured runoff data of seven hydrological stations,SWAT distributed hydrological model is constructed to simulate the potential evapotranspiration,actual evapotranspiration,runoff and other data under different land use conditions of different sub basins in 1980,1985,1995,2000,2005,2010 and 2015.Using weather generator to interpolate missing meteorological data and based on the Budyko coupled equation of water and heat,the method of elastic coefficient is used to analyze the runoff variation in Min-Tuo River Basin.The main contents and conclusions are as follows:(1)A SWAT distributed hydrological model suitable for the study area was constructed for mintuo River Basin,and 89 secondary subbasins were simulated for precipitation,potential evapotranspiration,actual evapotranspiration and runoff from 1981to 2014 by using the established model.The simulation results were better after the calibration and verification of the SUFI-2 algorithm in SWAT-CUP(R~2?0.70,NSE>0.60).(2)Based on the linear statistics,the evolution of hydrological regime and the interannual distribution of runoff in 1981-2014 were analyzed.It was found that the precipitation of Dadu River,Qingyi River,Minjiang River and Tuojiang River decreased at the rates of 11.5mm/10a,27.7mm/10a,14.2mm/10a and 20mm/10a,respectively.The potential evapotranspiration increased at the rates of 108.2mm/10a,3.7mm/10a,47.9mm/10a and 27.8mm/10a,respectively.Compared with the other three basins,the actual evapotranspiration of Qingyi River shows a significant downward trend,with a downward speed of 173.52mm/10a,and that of Dadu River shows a slow upward trend,with an upward speed of 77.51mm/10a.(3)In order to explore the causes of runoff changes in river basins,based on the Budyko water-heat coupling equation and watershed water balance equation,the runoff changes of 89 secondary sub-basins are analyzed.The results show that most of the average annual runoff in the influence period is significantly lower than that in the base period,and rainfall reduction is the main factor leading to runoff reduction.56.18%of the sub-basins have the dominant contribution rate of rainfall,and 37.08%of the sub-basins have the dominant contribution rate of potential evapotranspiration.Only 6.74%of the underlying surface changes in the sub-basin account for the dominant contribution rate.(4)The impacts of climate change and human activities on runoff are quantified on a seasonal scale.The results show that there are seasonal differences in the impacts of precipitation,potential evapotranspiration and underlying surface changes on runoff reduction.The impacts of precipitation on Runoff in 79.8%of the secondary sub basins are negative in the wet season,positive in the normal season,and small in the dry season.The effect of potential evaporation on 93.2%of runoff in the sub basin is more obvious in the wet season than in the normal and dry season.