IMPACT OF LAND USE/LAND COVER AND CLIMATE CHANGE ON SOIL EROSION IN SILE WATERSHED, LAKE ABAYA-CHAMO SUB BASIN, SOUTHERN ETHIOPIA

Abstract

The combined impacts of land use and climate change are significantly affecting natural resources, particularly soil and water ecosystems. Thus, studying the impacts of land use/land cover (LULC) and climate changes on soil erosion in the Sile River watershed is very essential for proper natural resource management. In this study, the historical change of LULC (from 1987-2020), prediction of 2050, the impact of changing LULC & climate on soil erosion for the years of 1987, 2003, 2020, and future 2050 under two climate scenarios (RCP4.5 & RCP8.5) were evaluated. The Landsat TM for 1987, ETM+ for 2003, and Landsat-8 OLI/TIRS for 2020 were used for LULC classification. Supervised image classification method with maximum likelihood classification (MLC) was applied in the ERDAS Imagine software. Classified historical LULC map serves as a baseline to predict 2050 LULC with considering different driver variables using Multi-Layer Perceptron Neural Network and Cellular Automata-Markov Chain Model integrated with TerrSet software. Daily rainfall data from 1987-2020,102 composited soil samples, ASTER DEM with a resolution of 30*30-meter and classified LULC map was used for erosivity (R-factor) estimation, soil erodiblity (K-factor) analysis, topography (LS-factor) computation, and for both practice (P-factor) and cover (C-factor) determination respectively. In addition, the ensemble means of four regional climate models (RCMs) rainfall data under two scenarios (RCP4.5 & RCP8.5) and predicted 2050 LULC map was used to generate R-factor and both P&C factors respectively for the estimation of 2050 soil loss. A revised universal soil loss equation model (RUSLE) has been used to compute the above factors in Arc GIS software to estimate the rate of soil loss. This study revealed that, in both periods from the year 1987- 2003 and 2003-2020, cultivation land, bare land, and banana land cover were expanded at the expense of shrubland, forest land, grazing land, and water body decline. Sile River watershed experienced substantial LULC alteration and will also be prolonged for the coming several years. The mean annual soil loss for the years 1987, 2003, and 2020 were 13.05, 21.04, and 41.41 t-ha−1 year−1 respectively. The lowest mean annual soil loss was observed in banana land cover and gently slope classes. While highest and severe was detected on bare land & steep slope classes correspondingly. The average soil loss under the RCP4.5 and RCP8.5 scenarios with a future 2050 LULC were predicted to be 56.48 t ha−1 year−1 and 57.11 t-ha−1 year−1 then it will be expected to increase 36.40 % and 38.19 % respectively. LULC, climate change/variability, and the steepness of slope had been believed to be the leading factors that exacerbated soil erosion in the study area. From the finding of this study, prioritized sub-watersheds are recommended for land management intervention, and disseminating banana plantations in the other part of the watershed was suggested. Additionally, climate change will aggravate the current soil erosion problem and would need ecological sound conservation policies and strategies to mitigate the adverse impacts of climate change on soil erosion.