Analysis of the Impacts of Land Use/Land Cover Change In Triggering Soil Erosion in Gilgel Gibe Sub-Catchment Of Omo-Gibe Basin; Southwest Ethiopia.

Abstract

Recently, Land Use and Land Cover Change (LULCC) and their impacts on natural resources have gained increased attention. This study aimed at analyzing the impacts of LULCC in triggering soil erosion using GIS and remote sensing techniques integrating RUSLE model in Gilgel Gibe sub catchment of Omo Gibe basin, Southwestern Ethiopia. To analyze LULCC during study periods, Landsat images of 1991 (TM), 2005 (ETM+) and 2019 (OLI/TIRS) were used. Additionally, Digital Elevation Model (DEM), computed Land Use/Land Cover (LU/LC) maps, rainfall and soil data were used as sources of data to analysis LULCC impacts on soil erosion and to identify the most erosion prone areas. Accordingly, cultivated land, settlement area and water body were increasing at the expense of sharply reduction in forest, bush and grass lands. The high level of conversion to cultivated land at the expense of forest and bush land classes is confirmed in the area which implies that how much the area is prone to soil erosion hazard. Results from RUSLE factors determination indicated that the highest value in R-factor, K-factor and LS-factor were more of recorded in areas with steep slopes of the study area whereas the highest value in C and P-factors are recorded in cultivated land and the lowest were in water body. The result showed that the annual mean soil loss which was 24.81ton/ha/yr. in 1991 was increased to 56.67ton/ha/yr. in 2005 and 83.6ton/ha/yr. in 2019. This is due to the expansion of cultivated land without appropriate conservation measures, increment of settlement area, with other factors such as spares land cover and steep sloping terrain are the main causes for the increasing of mean soil erosion rate. The spatial distribution of soil erosion risk classes between 1991-2019 showed an increasing trend in the study area, that is, it increased from slight, moderate to severe and very severe classes while areas under very slight soil erosion risk class decreased sharply. Furthermore, results indicated that the trend of potential soil loss in the three study years indicates that a sharp increase for cultivated lands, settlement areas, forest and bush lands; whereas the reduction of forest and bush lands LU/LC classes and an increment of cultivatedl and settlement LU/LC areas are the main indicators of LULCC impacts on soil erosion. Particularly, about 0.01% of area in 1991, 0.04% area in 2005 and 4.12% area in 2019 of the study areas was subjected to erosion prone areas which needs prior intervention for implementation of the soil erosion controlling mechanisms and the other mitigation measures