| Numerous interrelated elements impact water resources,including geography,rainfall,humidity,air temperature,soil and vegetation type,land use,and land cover.To predict future climate and its possible influence on hydrologic regimes,it is necessary to understand the existing Eco hydrologic processes for a watershed.The research basin comprises more than 20%of Ethiopia's geographical region,50%of the common annual runoff,25%of the population,and more than 40%of the country's agricultural productivity.The Upper headstream(Abbay)basin is abundant in both land and water.The basin,however,is under significant stress as a result of tiny and fragmented land holdings,soil and land degradation,diminishing crop yields,increased population,climatic unpredictability,desertification,and increasing upstream-downstream water usage disputes.Eco hydrological alterations may have resulted in changes to the hydro-climatic characteristics,ecology,ecosystem,and environmental conditions of the Abbay geographic region.Thus,identifying and characterizing ecohydrologically related processes,as well as forecasting future changes in streamflow in the Abby River Basin(ARB),is critical for basin system planning and management.In this study,the anticipated trends of yearly rainfall,air temperature,and river discharge at selected stations throughout the basin were examined using a combination of Mann-Kendall,Innovative trend analysis technique(ITAM),Sen's slope estimator test,and statistical analysis.The land cover and vegetation status were investigated using remote sensing,GIS analysis,land use/cover/cover categorization,and vegetation detection methods.The basin's water and environmental management were studied using statistical analysis,as well as analytical and synthesis methodologies.At five sites,the change in yearly temperature,precipitation,and river discharge variability was evaluated using the Innovative trend analysis approach,Mann-Kendall,and Sen's slope test estimator.Annual precipitation decreased in Assoa(Z=0.71),B ahir Dar(Z=0.13),and Gonder(Z=0.26),but increased significantly in Nedgo(Z=2.45)and Motta(Z=1.06).Annual temperatures have risen significantly in Assosa(Z=5.88),Bahir Dar(Z=3.87),Gonder(Z=4.38),Nedgo(Z=4.77),and Motta(Z=2.85).The average mean temperature has risen by 0.2? during the previous 36 years(1980 to 2016).In northern Ethiopia's semi-arid zone,exceptionally high temperatures were recorded.The land cover and vegetation of the study basin are quite vulnerable to climate change.This study also looked at climate change dynamics in selected basin stations during a 36year period(1980-2016).A novel trend analysis technique,Mann-Kendall,and Sen's slope estimator test were used to study mean annual precipitation and temperature variables.Remote sensing,GIS analysis,land cover classification,and vegetation detection methods were utilized to investigate the Abbay river basin's land cover and vegetation during a thirteen-year period(2001-2013).The NDVI,EVI,and Transformation matrix were used to evaluate the regional and temporal patterns of land cover and vegetation affected by climate change.The data show that over a 36-year period,the average annual temperature increased significantly(=0.12,Z=0.75),with temperatures rising by 0.5? and precipitation falling marginally.Forest area and water body decreased by 3429.62 km2 and 81.45 km2 correspondingly over a thirteen-year period,whereas grassland(2779.33 km2),agricultural land(535.34 km2),bare ground(43.08 km2),urban land(0.65 km2),and wetland(152.66 km2)all increased.The calibration and validation outcomes indicate that the employed hydrological model,VIC version,become found capable enough to represent the study basin hydrological response proving that it could be used for further analysis.The NSE and BIAS were used to evaluate the calibration,which was done using the Montecarlo auto-calibration process.The model captures the overall components of the hydrograph throughout the calibration and verification phases.Peak and low flows are overestimated and underestimated,respectively,due to the complex model structure and the uncertainty arising from the input data.The model was calibrated using observed runoff data,potentially leading to flood peak discharge.As a result,more observational facts units are likely to be required in the future to calibrate the version and increase simulation performance accuracy.When the five climate models are integrated,the projected water resources offer a variety of results.According to multi-model ensemble data,the mean annual runoff depth increases greatly in the northern mountainous area,slightly in the lowland,and decreases in the basin's central reaches.The mean yearly streamflow statistics show an increasing tendency over time in each of the three situations.Under the RCP4.5 scenario,yearly runoff in the Megech,Gilggel Abbay,and Temcha sub-basins is 25%,33.3 percent,and 10%more than in the baseline era.The overall trend is encouraging,although the average monthly runoff reduces by more than 20%in July across the three weather situations.Consistently the streamflow was projected to under most climate models and emission scenarios decrease in Gilgel Abbay and Temcha watershed which could be due to a decrease in seasonal flows.Nevertheless,all emission scenarios and climate models predicted that the long-term annual average streamflow in the Megech watershed will rise.Moreover,efforts were made to look at the hydropower potential under predicted climate change,and it was calculated that the hydropower potential during baseline is 907.3106 kw·h,and under RCP 2.6,RCP 4.5,and RCP 8.5 scenario,it is 989.6106,1049.2106,and 977.6106 kw·h,respectively.Although it rises throughout the year,its percentage falls during the flood season.Cascades reservoirs must be built in the upper and intermediate reaches of the river in the long term to enhance and exploit hydropower potential.Overall,the results of this analysis revealed that future changes in river discharge and the regional and temporal patterns of water resources should be predicted in varying degrees.In 2013,NDVI and EVI values in the southern part of the basin decreased by 0.1.The findings of this study reveal that there has been a significant change in eco-hydrology,which has devastated the ecosystem.Hydro-climatic changes,such as a rising trend in temperature and a decreasing trend in precipitation,influenced the basin's land cover and vegetation even more.Land cover modifications are caused largely by global and regional climate change,as well as anthropogenic activities,and have a substantial influence on the basin's hydroclimate and eco-hydrology systems.Researchers may be able to learn more about the relationship between ecosystems,land,water,and climate dynamics in the study basin as a result of the findings.These findings point to a hydro-climatic shift that raises air temperature while lowering precipitation,with downstream consequences for river discharge in the Abbay basin.The soil moisture content,as well as the land and vegetation cover,were all affected by these changes.It resulted in significant alterations in ecohydrological processes,which harmed the environment.This change is brought about by anthropogenic action.Integrating hydrological and biological processes into long-term water resource management in the Abbay river basin is crucial.To conserve the environment in the basin,more land should be protected under specific protection programs.Furthermore,due to wastes from agricultural fields,families,medical sectors,institutions,and enterprises,the study region,the Abbay river basin,is severely depleted.An attempt was made to understand the current state of Abbay river pollution and its impact on environmental sustainability using a qualitative approach.The findings revealed a knowledge deficit,a policy gap,and regulatory limits.Formulation of solid platform,implementation of optimal environmental policies and contemplation of river rehabilitation,based on ecosystem service approach,are advised to regulate and correctly sustain the environmental pressure.In order to understand historical changes and predict future trends,it is critical to examine streamflow behavior under expected climate change as well as analyze hydropower trends from previous decades.Land surface models are another way to better understand river dynamics.The Variable Infiltration Capacity(VIC)model was utilized to simulate runoff in this study.To obtain the best-fit parameters,1000 rounds of calibration were performed.The mean annual runoff statistics show a rising tendency over time,according to simulation findings from the three emission scenarios(RCP 2.6,RCP4.5,and RCP 8.5).In particular,the annual runoff in Megech,Gilggel Abbay,and Temcha sub-basins is 25%,33.3%,and 10%higher under the RCP4.5 scenario than during the baseline period.Furthermore,triggering factors that have a significant impact on the ecohydrological process in the study basin were assessed in a qualitative way to explore the connections between ecohydrological processes and the basin's hydro-climates.Numerous factors affect the ecohydrological processes of the Abbay River basin.Climate and human activity both have an impact on the basin's ecohydrological processes.The air temperature has risen as a result of global warming.This has influenced precipitation patterns.The volume of river discharge was influenced by precipitation and human activities.These processes have also changed the land cover and vegetation.As a result of climate and human causes,have resulted in eco-hydrological practices and environmental change in the basin.This research emphasizes the hydroclimatic field and investigates ecohydrological process development mechanisms in order to give ecological security,technical assistance,and decision support for the Abbay River basin's environmental degradation and effective rehabilitation. 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