Hydrological Impacts of Climate Change in Tikur Wuha Watershed, Ethiopian Rift Valley Basin

Abstract

According to Intergovernmental Panel on Climate Change (IPCC) rising of global surface temperature, sea level rises, arctic and land ice decrease, erratic precipitation and increase of CO2 concentration are the main indicators of climate change. The main objectives of the study was to investigate the possible hydrological impacts of climate change on stream flow and sedimentation in Tikur Wuha watershed, by downscaling canESM2 (Canadian Earth System Model of second generation) global climate model using Statistical Downscaling Model (SDSM). Based on IPCC recommendation baseline periods (1987–2016) were used for baseline scenario analysis. Future scenario analysis was performed for the 2020s, 2050s, and 2080s. canESM2 model consists of Representative Concentration Pathway (RCP) RCP2.6, RCP4.5 and RCP8.5 scenarios. Impact assessment on stream flow and sediment yield was done by Soil and Water Assessment Tool (SWAT) hydrological model. SWAT model performance in simulating monthly stream flow for the study area was satisfactory with R² (0.77 and 0.87), N_SE (0.70 and 0.77) and D (-16 and -9) for calibration and validation periods respectively. The result of downscaled precipitation and temperature reveals a systematic increase in all future time periods for all three scenarios; RCP2.6, RCP4.5 and RCP8.5 scenarios. These increases in climate variables are expected to result in increase in mean annual stream flow of 8%, 13%, and 15 % for RCP2.6 scenario, 17%, 24%, and 31% for RCP4.5 scenario and 14%,24% and 35% for RCP8.5 scenario for the 2020s, 2050s, and 2080s, respectively. This leads to increment of sediment yield from different sub watershed. The estimated soil loss rate from different sub-watersheds had ranged from 0.42 tons/ha/yr to 28.31 tons/ha/year (1987-1999), whereas the annual weighted average soil loss rate from the watershed was estimated 16.80 tons/ha/year (2000-2100). Future work need to consider studying the effects of different climate change adaptation strategies.

Keywords: Climate change Scenarios, Ethiopia, Hydrological impact, SWAT model

DOI: 10.7176/JEES/10-2-04

Publication date: February 29^th 2020