Runoff Characteristics,Attribution Analysis And Future Prediction Of The Cold And Arid Regions

Runoff is the main source of production and domestic water for residents in cold and dry areas.However,its ecological fragile and extremely sensitive to environmental changes.With increased global warming and human activities,analyzing streamflow changes,finding related factors,and projecting future streamflow changes can help water resources management and sustainable ecosystem development for dry-cold regions.Our study analyzed historical streamflow changes and explored possible causes using multiple statistical methods and observations including observed streamflow,climate forcing,land use and land cover type,vegetation coverage,and global atmospheric factors.The statistical methods are linear regression,Mann-Kendall test,partial correlation analysis,and multiple wavelet coherence.Second,we quantified the contribution of groundwater,rainfall runoff,and snowmelt runoff to streamflow and found dominant factors in influencing each contributor for the Manas River Basin using Snowmelt Runoff Model(SRM).Lastly,we bias-corrected future precipitation and maximum and minimum temperature from 5 regional climate models involved in the CORDEX-EA-1 project and projected future streamflow changes for the Manas River Basin with calibrated SRM driven by these bias-corrected climate data.The major conclusions are as follow:(1)This study investigated the change in runoff during 1954–2016 and its dominant environmental factors.The annual runoff significantly increased at a rate of 0.508×10⁸m³/decade,and the climate tends to be warmer and wetter.The regional environmental factors had larger impacts on runoff than the global environmental factors,and the natural factors outperformed human activities in controlling runoff.Among the regional and global environmental factors,NDVI and ENSO are the single factor mostly correlated with runoff,while NDVI-TMP and ENSO-PDO are the combined factors with the strongest relations on runoff,respectively.The accelerated melting of snow/glacier induced by the increasing temperature dominated runoff change,and the increasing water inputs from wetter climate play a second role in runoff.(2)We calibrated SRM-simulated and recognition each runoff component.Result indicating SRM is capable of predicting runoff in the Manas River Basin.We further found that snowmelt-and rainfall-runoff contribute 42%and 33%of annual runoff,respectively,suggesting that snowmelt/glacier meltwater are major supplies to runoff.Also,based on partial correlation and multiple wavelet coherence,we found precipitation dominates total runoff and rainfall runoff,while PCP-ET₀-NDVI contributes most to snowmelt runoff.Precipitation is positively correlated to runoff at a scale of 4–6 moths,while other factors at>32 months.(3)We projected future runoff and climate changes for the Manas River Basin.First,the climate forcing from five RCM outputs were statistically bias-corrected.The downscaled future climate data suggest future climate tends to be warmer and wetter.With the increase of greenhouse gas concentration,the increase of precipitation will decrease and the temperature will continue to rise.Under RCP 4.5 and 8.5,precipitation is increasing in most months,and winter temperature shows the largest increases than other seasons.Runoff is projected to increase with larger increases during spring and fall than during winter and summer.Also,the variance ratio in January,March,December are much higher than in other months.Snowmelt and rainfall runoff changes are complex with increased snowmelt runoff ratio due to higher temperature.Future rainfall runoff ratio under RCP 4.5 is larger than that of the historical period,while opposite for that under RCP 8.5.With intense and continuing climate change,the Manas River Basin would see increased snowmelt,less precipitation changes,and larger total runoff amount in the mid-21^stcentury.Earlier snowmelt likely results in higher spring runoff amount and may spring flood.Also,higher temperature reduces snowfall amount and less snow cover on the ground,accelerating glacier disappearance.With no constraints on increasing temperature,the Manas River Basin will be dry due to the glacier loss.Therefore,water resources management should take those scenarios into consideration to minimize the impacts of climate change on water resources.