Assessment of Groundwater Recharge Change Using WetSpass Model in the Birr Watershed, Abay Basin, Ethiopia.

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Addis Ababa University


Understanding the long-term spatial extent of environmental and LULC changes in different time epochs helps to evaluate the impact of climate and LULC changes on water resources. Therefore, estimating the spatial and temporal extent of groundwater recharge in response to climate and LULC changes are crucial for the proper management of the water resources in the watershed. This study quantifies the effects of climate and LULC change on groundwater recharge for the Birr watershed from 1990-2020 periods using WetSpass model. The LULC maps of the study area were classified from multi-temporal Landsat imageries of Landsat 5(TM), Landsat 7(ETM+), and Landsat 8(OLI) using supervised maximum likelihood classification algorithm. The accuracy of classified images was checked by overall accuracy and kappa coefficient. In the study area, agriculture, built-up, and bare land increases through time while grassland, forest, wetland, and shrubland decreases during the last three decades due population growth and rapid expansion of farmland. The monthly reanalysis of climatological satellite products of precipitation, temperature, and windspeed maps was prepared from the decadal average of 1990-1999, 2000-2009, and 2010-2020 for the model simulation. The trend of the climate change in the watershed were analyzed and tested by Mann Kendall test R programming software. The temperature in the watershed has increasing trend over the last 30 year and increase by 0.033oc per year. Whereas, rainfall and wind speed have no significant trend in 95% confidence level. Moreover, a 12m resolution ALOSDEM was used to delineate the watershed and to develop slop and elevation input maps. The slope and elevation maps were finally resampled to 30m resolution. The study result shows that the annual groundwater recharge in the watershed decreases on average from 162.3mm to 128.6mm in from the first phase to the second phase and declines to 121.2mm in the third phase. it is important to take LULC conservation mechanisms and environmental rehabilitation measures in the study area. The study gives a piece of baseline information about impact of climate and LULC on the groundwater recharge of the study area for policymakers and the society of the watershed.