Abrhame Weldeyohannes Gilgel, Marta Gebreyesus, Tesemash Abebe, Aberham Chernet, Zenebe Mekonnen, Kidus Belay, Kassahun Ture
With experimental proof, it is scientifically well known that the cause of climate change is related to anthropogenic green-house gas emissions. And, to test the occurrence and the effect of climate change, Global(GCM) and Regional(RCM) climate change scenario models have been developed and used in practice for more than a couple of decades. Then, several study results have evidently shown that the entire globe has dramatically experienced climate change, in a rapidly trend, due to recent emissions are the highest in history. One way of demonstrating the indication of this climate change possibility over localities is by dealing with GCM and RCM climate change scenario models through statistical or dynamical downscaling method. Thus the objective of this research is to develop climate change scenario for lower Awash River basin under high, medium and low representative carbon concentration path ways (RCPs: Rcp2.6, Rcp4.5 and Rcp8.5). And, our aim is to investigate and deliver comprehensive and remarkable information to concerned bodies and communities about climate change possibilities and impact over lower Awash River Basins of Ethiopia. The method engaged to generate climate change scenario for each RCPs is Statistical Downscaling Method (SDSM Version 4.2.9), using CanESM2 coupled general circulation model. Besides, statistical regression analyses such as Nash Sutcliffe Model Efficiency and R2 are manipulated in order to evaluate model performance. Then, the results in this study showed that regarding model evaluation, almost all the three climate stations in common, except on very few months, the model demonstrated good to excellent efficiency with calibration value (R2>0.95) and validation strength value (R2>0.90) in case of maximum and minimum temperature; whereas the value is relatively less during model evaluation in replicating and simulating the precipitation. While, regarding the results of climate change scenario projections, on most of the climate stations and over Lower Awash River Basins in aggregate, on some months and seasons a change in temperate ranges from a very minor rise (0.3 d0c) and from a very minor decrease (-0.2 d0c) to a large and significant increase (3.5 d0c) on some other months under low, medium and high Rcps in ascending order. Especially, significant changes are observed on the periods 2050s and 2080s than 2020s under each Rcps. The same is happened in a case of precipitation, in all periods (2020s, 2050s and 2080s) and under each Rcps. Further, similar to other’s study findings, the rise in minimum temperature (2.5 d0c) is anticipated to be larger than the maximum temperature (2.0 d0c), on temporal average under medium and high Rcps. When season wise change in minimum and maximum temperature prospect is considered, the Summer season is anticipated to experience the maximum or peak deviation; and Winter and Spring come next in order of magnitude. However, in case of precipitation, under each Rcps the reverse is likely to happen opposite to the order of temperature-peak-change related to seasons. In general, the study revealed indications of extreme weather events which result in introducing increased climate variability on monthly, seasonal and inter-annual outlook, especially in precipitation (one time very dry with probability of drought occurrence and the other time very wet with high probability of flood incidence) and one time extremely hot the other time extremely cold. However, more or less, an increasing trend is observed for both precipitation and temperatures starting from 2020s to 2080s in all cases of Rcps and time frames (monthly, seasonal and annual). In addition, seasonal shift in precipitation patterns like changes in onset and cessation of rainy seasons, shortened or shrink of rainy season and changes in mode of seasonal rain fall pattern (bimodal to mono-modal and vice versa) are observed to occur in the anticipated future climate change scenario. The other important finding observed in this study is that the climax or peak effect of the Climate Change is pronounced over lowlands than mid-land and highlands (Mille, Diredawa and Cheffa).
Conclusion: The climate models used in downscaling from global and regional level to local level have their own limitations associated in. So, by considering this fact the results achieved with CanEsm2 model is generalized and concluded as the following. In general, projected changes in temperature and precipitation extremes are likely to have moderate to significant negative impacts on various socioeconomic activities over the communities and natural ecosystems over Lower Awash River Basins.
Recommendation: Based on this study result we recommend that areas over Lower Awash River Basins require close monitoring. So, planning, developing and implementing effective climate change adaptation and mitigation strategies; and strengthening early warning and disaster prevention and response mechanisms shall exhaustively sustain against climate change impacts. And, another recommendation in account of this study result is that prioritizing climate change adaptation and mitigation to those low land areas which are going to be affected highly likely. In general, effective and efficient utilization of water resource are recommended for actualizing climate smart agriculture and lessen the negative impact of drought, flooding and reservoirs sedimentation.