Assessment of Climate Change Impact on stream flow of Baro-Akobo River Basin Case study of Baro Catchment

Abstract

In recent decades changes in climate have caused impacts on natural and human systems on all continents and across the oceans. Impacts are due to observed climate change, irrespective of its cause, indicating the sensitivity of natural and human systems to changing climate. One of the direct impacts of this climate change is on water resources development and indirectly for agricultural production, environmental quality and economic development which will lead again to difficult conditions for Human to live in. The objective of this thesis is to provide the understanding of the direction of climate change impact on the stream flow of Baro watershed which is the major tributary of Baro-Akobo basin, Ethiopia. The soil and water assessment tool (SWAT) model was used to simulate the stream flow using the meteorological data of thirty one years from 1986 to 2016. The model was calibrated for a period of sixteen years from 1990-2005 and validated for the observed data for eleven years from 2006-2015 and shows a good agreement with R2 = 0.90 during calibration and R2 = 0.93 during validation whereas NSE=0.66 during calibration and 0.61 during validation. Hypothetical climate change scenarios of precipitation from -20% to +20% at 10% interval and temperature change from 2oC ,and 3 oC for the period of 2050s and from 3.5oC to 6oC at 1.5oC interval for the period of 2080s under RCPs 8.5 was taken based on the IPCC 5th assessment set for African countries. Results of this procedure show the sensitivity of stream flow to climate variability. For example, a change of precipitation from -20% to +20% for constant temperature of 2oC gives an increment of stream flow by around 11% .Beside this, for a constant precipitation of 0% and variation of temperature from 2oC to 3 oC there is reduction of stream flow by average of 12.7%. This shows that the Baro Catchment will be more sensitive to the average increase in temperature than to the average decrease in rainfall, which shows the role of evapotranspiration in the water cycle. Overall, the result suggest, a decrease in stream flow of 12.73% for the period of 2050s (i.e.2046-2065) and 15.56% by the end of the 21st century (2080s) as a consequence of decreasing rainfall of -20% and increasing temperature of 6oC Scenarios (i.e. the worst scenarios)