USLE

USLE, the Universal Soil Loss Equation, is an empirical model used to estimate long-term average annual soil loss caused by sheet and rill erosion from rainfall and surface runoff. Developed by Wischmeier and Smith in the 1960s, it provided a practical framework for planning soil conservation on cultivated land and has been widely applied since.

The equation is A = R × K × LS × C × P, with A the estimated annual soil loss (typically tons per hectare per year). The five factors are: R, rainfall erosivity; K, soil erodibility; LS, slope length and steepness; C, cover-management; and P, support practices. R reflects rainfall energy and intensity; K represents soil's susceptibility to detachment; LS accounts for how slope length and gradient amplify erosion; C captures the protective effect of vegetation, crop residue, and tillage; and P represents erosion-reducing practices such as contouring, strip cropping, or terracing.

USLE has been revised into the Revised Universal Soil Loss Equation (RUSLE) and, more recently, RUSLE2. RUSLE incorporated improved rainfall data, land cover, and geographic applicability; RUSLE2 provides a more process-based, field-scale framework that can be integrated with GIS. The models are widely used to produce erosion-risk maps, compare conservation scenarios, and guide design of soil- and land-management practices.

Limitations include that USLE estimates mean annual erosion from sheet and rill processes on cultivated lands and is not designed for gully erosion, landslides, wind erosion, or sediment yield predictions. It assumes relatively homogeneous fields and relies on representative factor values, particularly C and P, with accuracy varying by site and data quality.