Effect of Land Use and Land Cover Change on Soil Erosion in Alaba Sub-Watersheds of Central Rift Valley Basin, Ethiopia

Abstract

The magnitude of soil erosion rates has been accelerating in the Central Rift Valley Area of Ethiopia due to land use and land cover change (LULCC). This study aimed to analyze the trends and changes in land use and land cover dynamics and to analyze the impact of LULC change on soil erosion over the Alaba Sub-Watershed, Central Rift Valley Area of Ethiopia. This study would help to plan and use appropriate land use planning, soil, and water conservation practices, thereby reducing soil erosion in the study area. The soil loss rates were estimated using an empirical prediction model of the Revised Universal Soil Loss Equation (RUSLE) outlined in the ArcGIS environment. During the study period between 1987 and 2018, the rate of change in cultivated land and bare land was raised by 9.09% and 1.08%, respectively. On the contrary, vegetation cover and grasslands had dropped by –2.03%, and -1.42% respectively. From trends of LULC changes, cultivated land revealed an increasing trend increasing from 181.28 hectares to 351.23 hectares for the period 1987 to 2018, respectively. On the other hand, vegetation and grasslands showed a declining trend from -271.92,-22.66 hectares to -305.91, -124.63 hectares, respectively. The findings of the study generally elucidate that the LULCC has a detrimental impact on soil erosion. The estimated total annual actual soil loss in the study landscape was 25707.77 tons in 1987, 29310.71 tons in 2000, and 31769.32 tons in 2018. It was also found that the mean annual soil loss rate of the study catchment was 22.69t/ha/yr., 25.87t/ha/yr. and 28.04t/ha/yr. in 1987, 2000, and 2018 respectively. About 35% and 42% of the Sub-watershed experienced high to very severe soil erosion in 1987 and 2018, respectively. The results indicate that the estimated erosion rate for about 39 % of the sub-basin area exceeds the maximum tolerable soil erosion threshold and this shows that the erosion risk condition is deteriorating in the study landscape. The top three priority levels delineated for urgent SWC measures represent those areas within the large increase in erosion risk levels, with an area of 188 hectares and accounting for 17 % of the sub-watershed area. Therefore, further detailed investigations based on data from primary and secondary sources would be important in identifying driving socioeconomic forces and consequences of LULCCs and suggesting possible alternative options to establish sustainable resource management practices in the study area.