Assessment of Potential Surface Water Storage Options to cope up with Climate Change and Variability, Part of Abbay river basin

Abstract

Water storage has a vital role to play in improvingcountry wide food security and building resilience for adaptation to climate change and variability. This study concentrates on assessing the impact of climate change & Variability on Medium to large size reservoirs (Natural and Artificial) on selected Tana and Fincha sub basins, part of Abbay river basin. Climate variability was dealt in terms of areal Coefficient of variation of rainfall at respective catchments and the relation with Total rainfall. The spatio temporal variation of rainfall was analysed using Surfer8.0 software withthe boundary of “bln” data of Abbay river basin border polygon shape file. Future climate change variables are projected using GCM (General Circulation Model) which is well thought-out as the most power full tool for estimating future climatic conditions. SDSM (Statistical DownScaling Model) and RegCM (Regional Climate Model) are applied for areal Downscaling of climatevariables. HadCam3 and ECHAM5 emission Scenarios are used for impact examination for SDSM and RegCM3 respectively. Daily rainfall runoff modeling and reservoir simulation was conducted using HEC-HMS. A Digital Elevation Model (DEM) of the study area was used to extract the physical characteristics of watersheds using Arc-Hydro and the Geospatial Hydrologic Model Extension HEC-GeoHMS. Then in HEC HMS, ten and five years of hydrological and climatic time series data were used for calibrationand validation respectively. Calibration and validation value of the selected catchments with Nash Sutcliffe and Coefficient of determination (R 2 ) criteria has been evaluated and the result differs from one catchment as good as Gilgel abbay with Nash 0.76 (0.93) and R 2 = 0.77 (0.95) on daily and monthly ten years calibration to 0.68 (0.91) and R 2 = 0.685 (0.92) five years validation to other as moderate as Megech catchment with Nash 0.57 (0.795)and R 2 = 0.58 (0.815) ten years calibration on daily & monthly basis to 0.56 (0.785) and 0.575 (0.79) five years validation. The quantified inflow volume to the reservoir showsannual decrease in volume of inflow for Megech and Amerti reservoirs with the two emission scenarios i.e. ECHAM5 and HadCam3 emission scenarios, increase in inflow volume with ECHAM5 and a decrease with HadCam3 for Gumera and Fincha reservoirs is observed. Finally, a decrease and increase in inflow volume with ECHAM5 and HadCaam3 emission scenarios respectively for Gilgel abbay reservoir is obtained. The average time based reliability of the reservoirs estimated to be more than 87% and their volumetric reliability reveals greater than 95%. The resilience of the reservoirs is above 50% and their vulnerability is less than 30% on average those reflects the criteria of good performance of the reservoirs.