Assessment Of Hydrological Processes And Ecological Effects In The Qinghai Lake River Basin

As the largest inland salt water lake in Qinghai Tibet Plateau,Qinghai Lake,which is not only an important ecological security barrier in China,but also a highland for the construction of ecological civilization in China,is replenished by Buha River,Quanji River,Shaliu River,Hargai River,Ganzi River,Daotang River and Heima River.It has an essential strategic position at the national and regional scales.Therefore,scientific understanding of the temporal and spatial variation law of hydrological process in Qinghai Lake Basin boasts great strategic significance for both regional ecological environment protection and sustainable development of natural resources and environment.However,the snowmelt process often occurs in the alpine region or the source of the river,the study area is located in the river-lake merged inland lake basin,the complex topography and local microclimate affect the runoff variation of the basin,the lack of measured data has affected the study of hydrological processes in the region and the calculation of ecological indicators such as NDVI in recent years due to the presence of aquatic plant such as Chaetoceros sp.in Lake Qinghai Lake.On the occasion of the establishment of Qinghai Lake National Park,how to predict the water resources and ecological effects assessment of seven important rivers in Qinghai Lake Basin accurately has gradually become a hot and difficult issue for the scholars at home and abroad.Therefore,Qinghai Lake Basin has been taken as the research object,the temporal and spatial differentiation characteristics of natural geographical elements such as climate,vegetation,hydrology,land use/cover change,landform and soil are comprehensively considered;moreover,calibration and validation a semi distributed HBV hydrological model based on snow melting process in Qinghai Lake Basin by means of hydrological model simulation,ecological model analysis and field investigation is constructed.The water resources of seven important rivers in the basin during the historical period(1980?2016)are simulated and inversed by parameter transplantation.On basis of the future climate change scenario prediction data set under CMIP6,the water resources of seven main rivers in Qinghai Lake Basin during the future period(2015?2064)are estimated in the successfully constructed hydrological model.The temporal and spatial variation characteristics of important variables of water cycle are analyzed in linear trend method,Mann-Kendall mutation test,sliding T Test and R/S analysis;Secondly,based on the spatial analysis advantages,correlation analysis and geographic detector statistical methods of Arc GIS platform,the spatial differentiation characteristics of climate change,land use change,normalized vegetation index(NDVI),Net primary productivity(NPP)and carbon sequestration are quantitatively analyzed.The findings reveal that the temporal and spatial evolution characteristics of the ecological environment in Qinghai Lake Basin from the perspective of multi spatial scales such as pixel and ecosystem type.Based on the variation characteristics of soil moisture content,electrical conductivity and air temperature at different depths measured on daily scales in Bird Island sample plot,Heimahe sample plot and Jiangxi ditch sample plot in the study area,combined with the measured climate data such as air temperature,precipitation,evaporation,relative humidity,wind speed and wind direction,the driving forces are identified while the influence mechanism of climate change and human activities on the hydrological process of Qinghai Lake Basin is clarified.The relative contribution of climate change and human activity factors of hydrological process variation is clarified.The main conclusions are as follows:(1)HBV hydrological model can effectively simulate the freeze-thaw process of ice and snow in Alpine region,so it can effectively simulate the hydrological process of Qinghai Lake River basin.The Particle swarm optimization is used to calibrate the model for each sub basin,the KGE,NSE and RMSE are used to evaluate the accuracy of the model.The results show that,in the Buha River basin,the model is more robust than that in the other river basins,k GE,NSE and RMSE are 0.88,0.77,10.21 and 0.79,0.76 and18.63,respectively,k GE,NSE and RMSE are 0.87,0.82,12.34 and 0.84,0.83,14.38,respectively.(2)From 1980 to 2016,the amount of water resources in the Qinghai Lake River basin is fluctuating and increasing.It is mainly because the precipitation in the northwest Plateaux Region has increased significantly in the past 50 years,such climate change has an important impact on river runoff and lake water levels.The trend rates of runoff variation in Buha River basin,Quanji River basin,Shaliu River basin,Haergai River basin,Ganzi River basin,inverted river basin and Heima River basin are 8.9×10~6m~3/10a,4×10~5m~3/10a,2.7×10~6m~3/10a,8×10~5m~3/10a,7×10~4m~3/10a,4×10~5m ~3/10a and 7×10~4m~3/10a respectively.Based on the analysis of the correlation of water resources quantity,it is found that there is a significant positive correlation between runoff and effective rainfall,evaporation,soil water content,surface groundwater content and deep groundwater content(p<0.001),the effective snow cover and snowmelt are negatively correlated with the effective rainfall,runoff,evaporation,soil water content,surface groundwater content and deep groundwater content(p<0.001).(3)The change of water resources in Qinghai Lake River basin from 2015 to 2064 is different under different climate change scenarios.In the SSP1-RCP 2.6 scenario,the runoff,effective rainfall,evaporation,effective snow cover and snowmelt,soil water content,surface groundwater content and deep groundwater content of the seven major rivers in the Qinghai Lake River basin all show a fluctuating upward trend,the soil water content,effective snow cover and snowmelt increase obviously in 7 major river basins.Under the SSP5-RCP8.5 scenario,the snow cover and snowmelt amount of the seven major rivers showe a decreasing trend,and the decreasing trend was obvious.On the whole,with the increase of greenhouse gas emission and temperature,the precipitation and temperature of Qinghai Lake basin will increase in the future,and the total amount of water resources will increase compared with the historical period.(4)Hydrological processes are closely related to ecological processes in the Qinghai Lake River Basin.The water resources amount,NDVI,NPP and carbon sink all show a synergetic change and an overall fluctuation increase trend.There was significant positive correlation between effective rainfall,evaporation and NDVI in Qinghai Lake River basin(p<0.05),the correlation coefficients were 0.530,0.596 respectively;The effective precipitation,evaporation,soil water content and NPP(1 year lag)show significant positive correlation(p<0.05),the correlation coefficient are 0.515,0.561,0.548respectively;There was a significant positive correlation(p<0.01)between the effective rainfall,the soil water content and the carbon sink,the correlation coefficients are 0.617,0.643,respectively;There is a significant positive correlation between evaporation and carbon sink(p<0.05),and the correlation coefficient was 0.604.The results of this study can be used to promote the construction of nature reserves in Qinghai Lake Valley,Qinghai Lake National Park,and implement and perfect the performance appraisal system of ecological civilization,to further improve high-precision,dynamic ecological protection to provide scientific and technological support and decision-making basis.