USLE‐M: Empirical Modeling Rainfall Erosion through Runoff and Sediment Concentration

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Abstract
Runoff is a factor in rainfall erosion, and models that include explicit consideration of runoff provide better predictions of erosion than models like the Universal Soil Loss Equation (USLE) and the revised USLE (RUSLE) that do not. The USLE‐M is a modified version of the USLE based on the rainfall erosivity factor for an event, which is the product of the 30‐min erosivity index (EI30) and the runoff ratio (QR). As a consequence, USLE‐M contains explicit consideration of the effects of soil, crop, and crop management on runoff and sediment concentration. Also, the explicit consideration of runoff means that values of many of the other factors used in the USLE have to be reevaluated because the effects of variations in factors like soil and crop management on runoff are now being treated separately from the effects on sediment concentration. We present examples of new values for the soil erodibility (K) and crop management (C) factors resulting from an analysis of data from USLE runoff and soil loss plots at a number of locations in the USA in terms of the new modified version of the USLE. The new K values varied from 1.4 to 3.9 times the USLE K values. The new C values varied from 1.1 to 32.3 times the USLE C values. Procedures are also outlined for obtaining first approximations of the new K and C values from existing USLE values. Because of the explicit consideration of runoff, USLE‐M will, as a general rule, predict event soil loss better than the USLE. The USLE and USLE‐M are equally effective in predicting erosion for impervious conditions (QR = 1) but the efficiency of the USLE decreases as the proportion of the rain infiltrating increases, while that of the USLE‐M does not.

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