Climate Change Impact Assessment on Water Resources of the Gumara Watershed, Upper Blue Nile River Basin

Abstract

Recently, there is growth in scientific evidence that global climate has changed , is changing and will continue to change. and Climate change is al so expected to aggravate current stresses on water resources availabilit y clue to rapid population growth and economic deve lopment. The major uncertainty in water resources management is the variability of water supply and demand pertaining to changes in climatic variables and in dynamics or river basins. Therefore. the water s upply potential of a river basin is sensitive to land use and climate changes. Hence, in many river basins steady climatic (stationary) conditions are no longer considered a valid assumption for sustainable water resources management. The aim of the study is to assess the potential impact of climate change on the water resources of Gumara watershed using reliability , resilience and vulnerability indices. Although quantitative estimation of effects of climate change water resources are essential for understanding and solving the potential water resource management problems associated with agriculture, power generation and water resource planning and management; the coarser resolution of General Circulation Models (GCMs) does not provide reliable estimates of meteorological variables at the appropriate scale required for regional impact assessments. Hence more reliable meteorological variables corresponding to future climate scenarios can be derived from GCMs outputs using the so-called downscaling techniques. In the study area, there is better access to data from 1971 to 2000, which is taken as a standard of 30-years base period for downscaling using Statistical downscaling model (SDSM). AR(l) and LARS-WG were used for fil ling in . miss i ng data and to extend records at Woreta station respectively. I n th i s study SDSM is used to downscale the HadCM3 GCM outputs, and dynamically downscaled RegCM3 scenario outputs are collected from IWMI to generate the possible future scenarios in the Gumara wat ershed . After setting up and calibrating H E C -H MS hydrologica l model, the downscaled meteorological variables were subsequentl y used as input to the model to si m ulate th e co rresponding current and future stream n o w. CROPW.t \T is used to esti mate future I rrigation requirement . F inally , the cli m ate change i mp act is assessed using the Re liabi l ity , R esilience and Vulnerabilit y indices . Generally the S DSM projected max imum and minimum temperature shows an increasing trend for the next century , but the precipitation shows decrease trend. I t is also observed that the reliabilit y inde x for all climate scenarios reveal above 91% , resi l ience inde x of above 96% and Vu l nerab i lity of less than 3 0 %. Hence, it is concluded that it has high capabilit y to meet the required target demand in 2 0 3 0s , and also it recover s q uic k ly from a fa ilure to meet t he de mand to satisfying the targe t draft. Based on t he result of performance i nd ices . the decision makers, concerned persons or an y w.uer u s ers in the area can be as s ured that the proposed irrigation proj ect has very good potenti a I to irrig a t e the re q uired area under 2 0 30 s cli m atic condition