Soil Loss Assessment using Revised Universal Soil Loss Equation (RUSLE), Remote Sensing and GIS - Case Study of Rwanda

Abstract

Erosion, a global concern, and a threat to developing countries was revealed as the major problem enhancing food scarcity and hindering economic growth. Consequently, the degraded ecosystem has affected land productivity due to a decline in soil health and depleted soil fertility which is triggered by land use/land cover changes. Rwanda is a small and land-locked, globally densely populated country. A land blessed with hilly and steep topography and tropical climate. Through the rivers draining the country, precious resources, viz. water, soils, and organic matter are seasonally lost exhibited by the muddy water and debris in the runoff and streamflow. In this study, the investigation of rain induced topsoil loss, Sediment Yield Potential, and erosional water hazard assessment over 8 sub-watersheds of Rwanda i.e., AKA, AKL, AKU, KIV, MUK, MUV, NYL, and NYU in the period between 2021 and 1981 has been carried out. The Revised Universal Soil Loss Equation (RUSLE) Model integrated with GIS and Remote Sensing was adopted to estimate long-term average soil loss, whereas the CORINE model was utilized to examine the risk caused by the erosional water and finally, the SYI model was employed to calculate Sediment Yield Index and to prioritize sub-watersheds for catchment area treatment plan that responds to the ecosystem conservation. The results of the study revealed that Rwanda is greatly affected by water erosion that is ultimately increasing, with the estimated soil loss rate of approximately 45.9, 44.95, and 117.58 t ha-1yr-1 in 1990, 2008, and 2021, respectively. The estimated average annual soil loss at the sub-watershed scale i.e., KIV, NYU, and AKA sub-watersheds fall under the very severe erosion category with a mean soil loss rate nearly to 212.40 t ha-1yr-1, 180.76 t ha-1yr-1, and 115.86 t ha-1yr-1, respectively. Additionally, agricultural fields experienced a loss of 50.1 tons per hectare per year between 2008 and 2021. The erosion hotspot assessments revealed that nationwide 24.6 % of the land is severely vulnerable and 48.7% is moderately prone to erosion risk. The SYI model revealed that NYU, AKA, and MUV sub-watersheds are more prone to erosion as compared to AKU, NYL, AKL, KIV, and MUK sub-watersheds. The SYI values range between 1297.2 to 1517.4 for the sub-watersheds. Finally, biological i.e., Afforestation, strip cropping, contour farming, etc, and structural interventions i.e., construction of check dams, deep trenches, and terraces were suggested as soil and water conservation measures. Land degradation, Land use/ land cover, Remote Sensing and GIS, RUSLE Model, soil and water conservation, Soil erosion hazards, Soil erosion rate, Sediment Yield Index