Mapping The Spatiotemporal Variation Of Water Yield And Analyzing The Impacts Of Influencing Factors In Blue Nile Basin,Africa

Water supply is a crucial ecosystem service in the Blue Nile River Basin where agriculture is the backbone of the economy.However,Blue Nile Basin is located in the most ecologically degraded region in the world which serves as the main source of water for Ethiopia,Sudan and Egypt in Northeast African.The water is characterized by uneven distribution both in time and space.Climate variability and land use land cover(LULC)change have caused spatiotemporal water supply variation.Quantifying and mapping water supply variation is,therefore,an essential step for sustaining water supply service of the ecosystem.The main purposes of this study is to introduce a new water yield model and demonstrate its applicability in the Nile River Basin for water yield calculation,mapping,and impact assessment.This study investigated the applicability of the Integrated Valuation of Environmental Services and Tradeoffs(In VEST)model with open access remote sensing data for water yield estimation,mapping and impact assessment.The combination of In VEST,statistical techniques,and Residual Trends analysis with both ground and satellite data were applied in this study.For the first time,this study evaluated the performance of four satellite-based rainfall products,estimated and mapped water yield,and partitioned the impact of LULC change and climate variability on the spatiotemporal water yield variation with In VEST model.First,performance evaluation of satellite-based rainfall products for water yield modeling has been conducted.The evaluation was carried out through direct comparison with the observed rainfall and through simulation of annual water yield using In VEST model for monthly,seasonal,and annual time scales.In general,the results show that the performance of satellite rainfall differs in time scale,topography,and method of evaluation.CHIRPS v2.0 rainfall product shows good performance both at monthly(R2 = 0.83)and annual(r = 0.85)time scales regardless of elevation.TRMM-3B43 v7.0 well performed over the mountainous area,which makes it the best rainfall data than other products at seasonal time scale(r = 0.86).CHIRPS v2.0 and TAMSAT v3.0 are equally applicable to that of gauged rainfall data for annual water yield simulation(Bias = 1.01 and 1.08 respectively).The findings of this study indicated the best performance of CHIRPS v2.0 and TAMSAT v3.0 satellite rainfall products,and hence,these products can be used for water management and decision-making process,particularly in the data-scarce watersheds like Blue Nile basin.Then estimation and mapping of water production,evapotranspiration,and rainfall of the RibbGummara watershed have been performed by using open-access data based on the results obtained from performance evaluation as stated above.Climate,soil and land use-related data to model the key components of the water balance were utilized.Maps of the key parts of water balance were also produced.The spatial patterns of Rainfall,actual evapotranspiration,and water yield show sharp decline from North to southern part of the study watershed.Our analysis confirms the ability of the In VEST annual water yield model to estimate water production capacity of different part of a basin in data-scare area.Finally,the water supply variation due to LULC and climate variability was calculated and disentangled using Residual Trends analysis.A significant increase in the water supply was observed due to the joint effects of climate variability and LULC change in the watershed(203 mm).The contribution of climate variability was 94% whereas LULC contributes only 6% from 2003 to 2017.Climate variability negatively led to water supply variation while LULC change contributed positively from 2010 to 2017.Although the ongoing soil and water conservation(SWC)practices improved vegetation cover and water retention of the watershed,climate variability is the main driver of water supply variation.Therefore,SWC practices should incorporate ecosystem-based climate change adaptation strategies and scale up to communitybased integrated watershed management to sustain water supply.