Impact of Climate Change on Hydrological Responses of Gumara Catchment, in the Lake Tana Basin - Upper Blue Nile Basin of Ethiopia

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Addis Ababa University


Predictions of the impacts of climate change on the intensity, amount, and spatial and temporal variability of rainfall and temperature are required. The aim of this study was to assess the status of climate change and hydrological response to climate change for Gumara River sub-basin. The HadCM3A2a and HadCM3B2a (Hadley centre Climate model 3), output of Global Circulation Model (GCM), scenarios of climate change were used for predicting the future climates of the study area. Statistical Downscaling Model (SDSM 4.2) was used to downscale large scale predictors into finer scale resolution. To estimate the level of impact of climate change, climate change scenarios of precipitation and temperature were divided into four time windows of 25 years each from 2001- 2099. The Soil and Water Assessment Tool (SWAT) was used to simulate the hydrological response. SWAT was first calibrated and validated using observed data and the SDSM downscaled climate outputs were used as an input into the SWAT model to assess the hydrological responses of Gumara River due to climate change. The period from 1986-2000 were taken as a base period against which a comparison was made. The results showed that the SWAT calibration and validation reveals a good agreement with R2=0.9 during calibration and R2=0.89 during validation whereas NSE= 0.89 during calibration and 0.86 during validation. The monthly and seasonal downscaled precipitation, maximum and minimum temperature in the future time horizons did not show systematic increase and decrease i.e. increases in some months and season and decreases in some other months and seasons. Annually, both precipitation and temperature showed increasing trends in all future time horizons (Precipitation increases up to 13.7% while temperature increases up to a maximum of 1.01oc). Based on monthly, seasonal and annual changes of precipitation, maximum and minimum temperature, the SWAT model was rerun for each time horizons and the results reveal, as that of precipitation and temperature, the monthly flow volume did not show systematic trends i.e. increases from month of April-September up to a maximum of 134.54% for A2a and 127.52% for B2a and decreases in the remaining months by 47.44% (A2a) and 46.62% (B2a). Seasonal and annual flow volume increases in all future time horizons as compared to the base period. Seasonally, the maximum increment was shown in the major parts of the rainy season (Kiremit) and small rainy season (Belg) in which the flow volume increases by 144.65% for A2a scenario and 101.58% for B2a scenario. Moreover, the annual increment showed systematic trends and the increment reaches up to 17.65% for both scenarios at the end of 21st century. Thus, the hydrology of Gumara River is highly vulnerable to climate change especially in the rainy seasons which causes high floods and therefore, considering climate change impacts is advantageous in any water related issues on Gumara sub-basin. Key words: Blue Nile, Gumara River, Climate Change, SDSM, Hydrological Modeling, SWAT Model Lake Tana Basin, Ethiopia



Blue Nile, Gumara River, Climate Change, SDSM, Hydrological Modeling, SWAT Model Lake Tana Basin, Ethiopia