Assessing Climate Change Impacts On Water Availability In Upper Awash Sub-Basin, Ethiopia.

Abstract

Variations And Change In Climate In The Past Has Influenced And Will Continue Influencing The Availability Of Water. This Study Assessed The Likely Impacts Of Climate Change On Water Availability In The Upper Awash Sub-Basin Using The Soil And Water Assessment Tool (Swat). The Study Specifically Analyzed The Historical Trends In Precipitation And Temperature, Downscaled The Projected Climate Variables (Temperature And Precipitation) For The 2030s (2021-2040) And 2050s (2041-2060) For The Upper Awash Sub-Basin And Estimated The Impacts Of The Projected Variables On Stream Flow. Dynamical Downscaling Method Was Used To Downscale The Future Climate Data From Cordex Africa Using Regional Climate Models And Bias Correction Was Done Using Delta Change Approach Method For Hydrological Impact Analysis. The Period 1985-2014 Was Considered As The Baseline Period Against Which Comparison Was Made. In Assessing Historical Precipitation And Temperature Trends, Mann-Kendall Trend Test Were Used. Results For The Mann-Kendall Tests Showed A Declining Trend In Precipitation And A Statistically Significant Rising Trend In Maximum And Minimum Temperature. The Results Of Downscaled Maximum And Minimum Annual And Monthly Temperature Reveal That There Is Increase In Temperature For Both Rcp4.5 And Rcp8.5 Scenarios At 2030??S And 2050?�?S. However, The Result Of Downscaled Rainfall Shows Decrease In Annual And Both Increase And Decrease Mean Monthly Rainfall For Rcp4.5 Scenario And Decrease For Rcp8.5 Scenario. Dynamically Downscaled Climate Outputs Were Used As An Input To The Swat Model For The Future Impact Assessment. Performance Of The Swat Model Was Evaluated Using R2, NSE, And Pbias. During Calibration (1999-2003) Of The Model, Values 0.82, 0.78 And 11.23% Were Obtained For R2, NSE, And Pbias. Whereas During Validation Period (2004-2006) Values 0.78, 0.75 And 8.9% Were Obtained For R2, NSE, And Pbias. Besides, The Uniformly Scattered Points Along The 1:1 Line During Calibration And Validation Justify That The Model Is Good In Simulating Stream Flow Of Upper Awash Sub-Basin. The Total Annual Surface Water Resource Potential Of Upper Awash Sub-Basin At The Base Period According To This Study Is Estimated To Be About 3.302bcm/Year. However, In 2030??S Increasing Water Availability Is Shown By 3.83% And Decreased By 2.32% In 2050s Under RCP 4.5 Scenarios. Similarly, Water Availability Reduces By 34.04% And 37.57 % In 2030s And 2050s Respectively Under Rcp 8.5 Scenarios.