Assessment of Changes in Soil Erosion Risk Using RUSLE in Navrood Watershed, Iran

Risk assessment of soil erosion, one of the most important land degradation problems worldwide, is very essential for land and water resources management, and development of soil conservation methods. In the present study, the temporal changes of soil erosion risk were assessed from 1987 to 2010, based on the Revised Universal Soil Loss Equation (RUSLE) using Remote Sensing (RS) and Geographic Information Systems (GIS) for the Navrood Watershed, Iran, with an area of 270 km(2). Two Landsat satellite imageries obtained in 1987 and 2010 were used to assess the changes in vegetation cover during this period, and to obtain the Cover factor (C) of RUSLE. Rainfall and soil texture data and a digital elevation model were used to calculate the rest of RUSLE factors, which were taken as constant for the study period. The results showed that the average annual soil loss over the watershed ranged from 0 to 1,056 t ha(-1) y(-1) (Cumulative percentage > 99.9%). The area mapped as very high erosion risk (> 100 t ha(-1) y(-1)) increased from 10% in 1987 to 12% in 2010, and the area of the next risk class (51-100 t ha(-1) y(-1)) increased from 8 to 9%. These changes cover an area of about 800 ha in the watershed, in which erosion risk has been doubled or tripled in the last 23 years. Forest clearing and rangeland overgrazing were identified as the most important reasons for the increase in erosion risk.