Simulation of the Hydrological Impacts of Climate and Land Use/Cover Change on Tikur Wuha Watershed in Ethiopia

Abstract

The study was carried out on the Tikur Wuha watershed (TWW) in Ethiopia with four specific objectives: simulation of the potential impact of climate change on hydro-meteorological variables, evaluation of the hydrological impacts of land use/cover (LU/LC) change, examination of the trend and variability of hydro-meteorological variables, and prioritisation of the sub-watersheds for soil and water conservation (SWC) measures based on soil loss rate (SLR). The LU/LC map was developed using a supervised classification method. The impact of LU/LC and climate change on streamflow was assessed using the Soil and Water Assessment Tools (SWAT) hydrological model. The Mann-Kendall trend test and Sen's slope estimator were employed for the trend and size of the trend, respectively. A Universal Soil Loss Equation (USLE) was used to estimate the SLR. The result revealed that the Bega, Kiremt, and annual rainfall increased for all scenarios. In contrast, the Belg rainfall decreased in all cases except for RCP8.5 at the end of the century. Both the minimum and maximum temperatures increased for all scenarios. The annual average streamflow in TWW increased in all cases except a slight reduction in the RCP4.5 scenario in mid-century. Climate change affects the streamflow in the study watershed by increasing the wet season flow and reducing the dry season flow. The LU/LC detection shows a steady expansion of cropland and built-up areas and the withdrawal of shrubland, swampy, water bodies, and grassland during the 1978 to 2017 periods. The LU/LC changes increased the average annual streamflow by 14.77% from 1978 to 2017. The LU/LC change had a dominant role in the hydrological responses of the TWW. The trend analysis discovered that the average annual rainfall exhibited an insignificant declining trend of 20.8 mm/decade at a watershed scale. The temperature showed a statistically significant rising trend, with the minimum temperature rising faster than the maximum temperature. The Tikur Wuha River's streamflow increased at 21.16 MCM/decade from 1980 to 2002. The average SLR of the watershed is 14.13 t ha-1yr-1. It is larger than the maximum soil loss tolerance of the watershed and higher than the country's average SLR. The SWC measures should be implemented rapidly in the TWW, consistent with the priority watersheds' rank.