Study On The Changes Of Hydrological Processes In The Ulagai River Basin And Their Effects On Ecosystem Quality

In recent years,global warming and continuous human activities have significantly altered the hydrological cycle and the closely related ecological environment of inland river basins in arid and semi-arid regions.In order to gain insight into the synergistic evolutionary effects of changing environments on hydrological processes and ecosystems in this type of region,this study selected a typical inland river basin in arid and semi-arid region,the Ulagai River basin,as the study area.Based on multi-source remote sensing and ground monitoring data,the improved SWAT hydrological model(Soil and Water Assessment Tool)was used to simulate the hydrological process factors in the Ulagai River basin from 1982 to 2018.Meanwhile,the Remote Sensing Ecological Index(RSEI)was constructed using normalized vegetation index,precipitation,leaf area index,surface temperature index,and temperature vegetation drought index to evaluate the ecosystem quality of the Ulagai River basin from 1982 to 2018.In addition,the synergistic evolution characteristics of hydrological processes and ecosystems in the Ulagai River basin were explored by combining gray correlation and Pearson correlation analysis.On this basis,the internal and external relationships of the synergistic evolution of hydrological processes and ecosystems in the basin were further explored by combining data such as population and gross product.The following conclusions were obtained:1)The SWAT model simulations of the Ulagai River basin are good,the rate regular and validation period NSE and R~2 are higher than 0.6,PBLAS are less than 20%.In addition,MODIS snow area and evapotranspiration data and model simulation values correlation coefficient are higher than 0.8.The simulation results show that the basin evapotranspiration from 1982～2018showed a significant increasing trend,precipitation,surface runoff depth,lateral flow,and groundwater recharge and snowmelt all showed decreasing trends;and the runoff depth changed abruptly in 2000.Spatially,the spatial distribution characteristics of more precipitation and snowmelt and smaller runoff depth in the northeastern part of the basin,and more evapotranspiration,surface runoff and lateral flow in the downstream area.The hydrological processes in the Ulagai River basin from 1982 to 2018showed a decreasing trend,and climate change was the main factor leading to the decrease of hydrological process factors;the contribution of climate change was 95.84%,which reduced the runoff depth by 40.07 mm;the contribution of human activities was 4.16%,which reduced the runoff depth by 1.74 mm.During the study period,the contribution of climate change to runoff gradually decreased,while human activities gradually became the dominant factor,increasing from 11.74%to 74.53%.In addition,the total water yield in the Ulagai River basin in different surface states showed a trend of increasing,then decreasing and then increasing,with a decrease of 21.4 mm in the total water yield from 1981 to 2000.2)The ecosystem quality of the Ulagai River basin showed a non-significant decreasing trend at a rate of 0.001/yr from 1982 to 2018,with a multi-year mean of 0.41,indicating that the overall ecosystem quality of the basin is at a moderate level(level III).During the study period,the ecosystem quality was the best in 1985 and the worst in 2000,which was at a lower level.The distribution pattern of ecosystem quality in the basin gradually gets better from east to west.The area with the best ecosystem quality(level V)was concentrated in the upper part of the basin,with an area of 1.21%,and the worst area(level I)was in the area around the wetlands in the lower part of the basin,with an area of 21.11%.During the study time period,the overall ecosystem quality of the Ulagai River basin showed a decreasing trend(slope>0),accounting for 88.9%of the total basin area.3)The correlations between basin evapotranspiration,precipitation,snowmelt,lateral flow,runoff depth,and groundwater recharge and ecosystem quality during 1982-2018 were 0.96,0.92,0.88,0.88,0.78,and 0.72,respectively.the correlations between hydrological process factors and ecosystem quality at the sub-basin scale were all higher than 0.65.The correlations between hydrological process factors and ecosystem quality during1982～2018 in the upper and southern part of the lower basin had the strongest synergy between hydrological process factors and ecosystem quality,while the central part of the basin was less synergistic.The population size and gross product of the Ulagai River basin showed an increasing trend from 1982～2018.Population growth and economic development have increased the use of water resources and increased the burden on grasslands.The implementation of a series of ecological restoration policies has effectively expanded the area of grasslands and woodlands in the basin,resulting in an improving trend in ecosystem quality.However,there is still a slight degradation trend in the overall ecosystem quality of the basin during 1982～2020 due to extreme droughts,dust storms,human activities such as agriculture and industry in the basin,and the degree of policy implementation.All these human activities have had an impact on the synergistic evolution of hydrological process factors and ecosystem quality in the basin.