Estimation of Soil Erosion in Nepal Using a RUSLE Modeling and Geospatial Tool

Soil erosion is a major issue, causing the loss of topsoil and fertility in agricultural land in mountainous terrain. Estimation of soil erosion in Nepal is essential because of its agriculture-dependent economy (contributing 36% to national GDP) and for preparing erosion control plans. The present study, for the first time, attempts to estimate the soil loss of Nepal through the application of the Revised Universal Soil Loss Equation (RUSLE) model. In addition, it analyzes the effect of Land Use and Land Cover (LULC) and slope () exposition on soil erosion. Nation-wide mean annual soil loss of Nepal is estimated at 25 t ha(-1) yr(-1) with a total of 369 million tonnes (mT) of potential soil loss. Soil erosion based on the physiographic region of the country shows that the Middle Mountains, High Mountains, High Himal, Chure, and Terai have mean erosion rates of 38.0, 32.0, 28.0, 7.0, and 0.1 t ha(-1) yr(-1). The soil erosion rate by basins showed that the annual erosions of the Karnali, Gandaki, Koshi, and Mahakali River basins are 135, 96, 79, and 15 mT, respectively. The mean soil erosion rate was significantly high (34 t ha(-1) yr(-1)) for steep slopes ( > 26.8%) and the low (3 t ha(-1) yr(-1)) for gentle slopes ( < 5%). Based on LULC, the mean erosion rate for barren land was the highest (40 t ha(-1) yr(-1)), followed by agricultural land (29 t ha(-1) yr(-1)), shrubland (25 t ha(-1) yr(-1)), grassland (23 t ha(-1) yr(-1)), and forests (22 t ha(-1) yr(-1)). The entire area had been categorized into 6 erosion classes based on the erosion severity, and 11% of the area was found to be under a very severe erosion risk (> 80 t ha(-1) yr(-1)) that urgently required reducing the risk of erosion.