Assessment Of The Uncertainty Of Runoff And The Water Shortage Risk In The Tarim River Basin Under The Impact Of Climate Change

The arid region of Northwest China,which located in the hinterland of Eurasia with dry climate and scarce rainfall,and almost all rivers in this region originate from mountainous areas.However,due to the scarcity of meteorological and hydrological observation sites in mountainous areas and lack of data,the uncertainty assessment of runoff under the influence of climate change has become a difficult problem.To solve this problem,this study takes the Tarim River basin as a typical representative of the inland river basin in the arid area of Northwest China.Based on the multi-source data,this paper reveals the uncertainty of runoff and the risk of water shortage in Tarim River Basin with a comprehensive method under the historical period and RCP4.5 climate scenarios.The characteristics and uncertainties of runoff change,the correlations between runoff and climate change,the uncertainties of climate change affecting runoff,the change of supply and demand of crop irrigation water demand and the risk of water shortage were analyzed by using multiple indexes of uncertainty measurement and the water shortage index,combining with recursive calculation method of water regime change,time series analysis and correlation analysis of climate and hydrological variables.The results of this study can provide a reference for a scientific understanding of the uncertainty of runoff change under the influence of climate change in the Tarim River Basin,and rationally develop runoff and formulate adaptive policies for water resources under climate change.The major findings are summarized as follows.(1)The uncertainty of runoff change in Tarim River Basin is mainly manifested in the large change amplitude,frequently shifted state of wet and dry,and the change cycle of runoff and monthly water inflow also have uncertainties.From 1965 to 2015,the state of wet and dry in the Tarim River Basin was transferred about 30?50 times.Moreover,runoff has various drought characters in different time-scales,with the alternating frequency of drought change about 60 times and about 20?30 times on the six-month scale and the twelve-month scale respectively.The uncertainty in the change period is manifested in the annual runoff has a significant period of about 2?3 years,which variance contribution accounts for about 24.79%?73.03%,and with the increase of time scale,the differences in the change period of runoff in each sub-basin are expanded.The uncertainty of the inflow mainly shows that the monthly inflow is obvious decrease and the annual inflow frequency is increase with the upward of drought grade.When the drought grade rises by one level,the average monthly inflow in Aksu River Basin,Kaikong River Basin,and the mainstream area decreases about21.53%?49.35%,26.24%?46.16%,and 34.83%?63.84%,respectively.(2)Runoff in the Tarim River Basin has multi-scale correlation and lag correlation with precipitation,temperature and potential evapotranspiration.The annual runoff in the source region has a significant positive correlation with annual precipitation and annual average temperature,while it has no significant negative correlation with annual potential evapotranspiration.Moreover,annual runoff presents in-phase change with annual precipitation and annual average temperature,with the high-energy resonance regions during the study period.From the lag response of runoff to regional climate change,the lag time of runoff to precipitation change is shorter than that to temperature and potential evapotranspiration.The lag time of runoff to precipitation change is about0.08d?0.85 d,while the lag time to temperature and potential evapotranspiration is about 0.68d?3.01 d and 0.10d?2.22 d,respectively.(3)Runoff in the Tarim River basin is sensitive to climate change,and the uncertainty of runoff is different in different time scales,which uncertainty is relatively greater in summer and autumn.Runoff is positively sensitive to the variation of precipitation,temperature,and potential evapotranspiration.When the annual precipitation and annual average temperature change by 1%,the annual runoff will increase by 2.5767%?2.9990% and 0.6784% ?2.7398%,respectively.And,when the annual potential evapotranspiration changes by 1%,the annual runoff will decrease by-1.9991%?-1.5767%.Considering the impact of precipitation,temperature,and potential evapotranspiration on runoff,the runoff change caused by climate change presents an increase in runoff depth.Since 1965,the changes in runoff depth caused by climate change in Yarkant River Basin and Aksu River Basin are relatively large,which are about 26.86mm?64.87 mm and 7.67mm?104.77 mm.The change is greatly influenced by precipitation and temperature,with the contribution rates of precipitation and temperature about 60%?92% and 11%?70%.The contribution rate of temperature to runoff change increases obviously during the study period.Moreover,the impact of climate change on runoff is uncertain,when precipitation and temperature changes have the uncertainty of 5.76%?6.96% and 22.26%?66.72%,the runoff change under the influence of climate change shows the uncertainty of 5.93%?18.23%.(4)Under the RCP4.5 climate scenario,the uncertainty of runoff in the Tarim River Basin in the next 30 years(2021-2050)will increase.Runoff still has the characteristics of large amplitude and strong volatility,and the uncertainty of runoff in summer and autumn is relatively strong and has increased compared to historical period.Also,the monthly inflow shows unstable due to the drought in the future.Affected by drought,compared with the historical period,the inflow reduction of Aksu River Basin,Kaikong River Basin,and the mainstream area in July and August increased by about 47%?88%,13%?42%,and 8%?24% respectively.As the drought grade upward by one level,the inflow in spring and summer of Aksu River Basin decreased by 8.49%?16.83%,and the inflow in summer and autumn of Kaikong River Basin and the mainstream area decreased by 0.13%?1.51% and 11.47%?21.41% on average.Under the RCP4.5climate scenario,runoff change has positive correlation with climate change in the Tarim River Basin.The runoff change caused by climate change in Aksu River Basin is relatively large,ranging from 149 mm to 196 mm.Besides,the uncertainty of future climate change affecting runoff has increased compared to the historical period,with the uncertainty ranging from 6.39% to 19.51%,which has increased by 0.47% to 1.28%compared to the historical period.The increasing amplitude of uncertainty in the Aksu River Basin is relatively great at about 1.28%.(5)Surface runoff is the main source of agricultural water in the Tarim River Basin,and the uncertainty of runoff has exacerbated the contradiction between the supply and demand of crop irrigation water.The imbalance between supply and demand is more prominent in spring,and seasonal water shortages of varying degrees exist in the source areas.In flood season,the runoff is large,which can basically meet the irrigation demand of crops,so there is almost no contradiction between supply and demand.In addition,there is a risk of water shortage in Tarim River Basin,and the risk of water shortage is gradually increasing,which makes it difficult for runoff to fully meet the irrigation needs of crops.Under RCP4.5 climate scenario,Kashgar River Basin,Yarkant River Basin and Weigan-Kuqa River Basin are always in a state of mediumhigh water shortage risk,and the water shortage risk is increased compared with the historical period,with water shortage index of 0.6?1.0.