Runoff Simulation And Prediction In The Kaidu River Basin Under Scenarios Of Land Use And Climate Change

The local hydrological cycle system changes correspondingly with the change of global meteorological environment and land use cover.It is a hot spot in water science research to quantitatively distinguish the impact of the two on local hydrological cycle and water resources.Based on the SWAT hydrological model,this paper selects the Kaidu River in the arid area as the study area,and uses the CN05.1 meteorological grid data to construct the SWAT hydrological model suitable for the Kaidu River basin under the support of Arc GIS platform to study the changes of runoff process under different climate and land use scenarios in the historical period(1981-2016).The runoff change trend of Kaidu River Basin under different climate and land use scenarios is predicted in the future(2021-2050).The main results of this paper are as follows:(1)Analysis of the characteristics of climate change in the watershed:From 1961 to2016,the annual average temperature in the middle and upper reaches of the basin was-3.38?,and the temperature increasing rate reached 0.26?/10a in recent 56 years;The temperature increases rapidly in winter and summer,both exceeding 0.28?/10a,and the lowest in autumn,which is 0.22?/10a;The temperature series changed abruptly in 1996;The average annual precipitation is about 334.94 mm,and increases continuously at the rate of 9.7 mm/10a;The increasing rate of precipitation in each season of the year is as follows:summer(1.75 mm/10a)>winter(0.68 mm/10a)>autumn(0.49 mm/10a)>spring(0.30 mm/10a);The precipitation sequence changed abruptly in 1986.(2)Analysis on the characteristics of land use change in watershed:According to the analysis of the change characteristics of the historical land use map of the river basin in1990,2000 and 2015,the grassland area was the largest in 2015,accounting for 43.77%,followed by the unused land area(34.93%),and the construction land area accounted for the least,accounting for only 0.29%;The transformation of grassland,unused land and cultivated land is the most obvious;The overall change of woodland and water area was not obvious in the past 25 years,while the woodland decreased at first and then increased,while the water body showed the opposite;The area increasing rate of 40.21%in recent15 years is construction land.The land use type map of Kaidu River in 2016 obtained by FLUS model has a Kappa coefficient of 0.92,which is accurate enough to be used to predict land use types in the future watershed.(3)Construction and evaluation of hydrological model:In the rate-setting period(1995-2005)of the SWAT model of the Kaidu River basin,R~2(determination coefficient),NSE(Nash efficiency coefficient)and Re(relative error)were 0.83,0.82 and-4.36%,respectively;During the verification period(2006-2016),R~2,NSE and Re were 0.76,0.72and 1.21%,respectively,far exceeding the evaluation criteria,indicating that the SWAT model can be used to simulate the runoff change process of the Kaidu River basin.(4)Simulation of runoff change process in historical period:(1)The impact of climate change on runoff:based on the impact of climate change on runoff in the historical scenarios S1(1981-1992),S2(1993-2004)and S3(2005-2016),the interannual variation of runoff increased at first and then decreased.In summer,autumn and winter,the runoff first increased and then decreased,and only the spring runoff increased continuously;(2)The influence of land use change on runoff:the influence of the change of historical land use data on runoff is relatively small,which increases at first and then decreases,and the runoff in summer and autumn also increases at first and then decreases,while the runoff in spring is on the contrary.Only in winter runoff continues to decrease.(3)The impact of both on runoff:from S1 to S2,both increased runoff,in which the contribution rate of climate change was 95.41%,and that of land use change was 4.59%from S2 to S3.Both of them reduced runoff,the impact of climate change reached 99.58%,and the impact of land use change was only 0.42%.(5)Runoff forecast in the future(2021-2050):when only the land use pattern is changed,the runoff under the natural development scenario and ecological protection scenario increases,while the runoff under the economic construction scenario decreases,but the degree of change is not great;Only when the climatic background is changed,the surface runoff increases to a great extent,and the annual runoff under the RCP8.5 climate background is higher than that under the RCP4.5 climate background;Combining future climate scenarios(RCP4.5 and RCP8.5 scenarios)and future land use types(natural development,ecological protection and economic construction scenarios)to predict the runoff from 2021 to 2050,the runoff of the watershed shows an increasing trend from2021 to 2050.no matter what kind of climate background scenario,the average annual runoff is natural development scenario>ecological protection scenario>economic construction scenario.