Extension and validation of a geographic information system–based method for calculating the Revised Universal Soil Loss Equation length-slope factor for erosion risk assessments in large watersheds

A geographic information system-based (GIS) method for estimating the lengthslope (LS) factor of the Revised Universal Soil Loss Equation using national-scale datasets was developed and validated. The method was applied to approximately two-thirds of the Mississippi River basin, focusing on agricultural subwatersheds in the Midwest. The results were validated by comparing the GIS-based statistical distributions of LS-factor values with the distribution of LS-factors calculated from the Natural Resources Inventory database at the eight-digit watershed level. The GIS-based approach was shown to produce statistical distributions of LS-factor values very similar to those described by the Natural Resources Inventory database of field measurements, providing for the first time strong support for using GIS-based methods to represent the spatial heterogeneity and magnitude of LS-factors. Development and validation of the GIS-based approach is an important step toward conducting large-scale erosion potential assessments that have soil conservation implications in natural resources management, agronomy, and agrochemical exposure risk assessments.