A National-Scale Method for Estimating the Rainfall Erosivity Factor (R) from Daily Rainfall Totals in Mexico

Rainfall erosivity is a key driver of soil erosion and a fundamental input to the Revised Universal Soil Loss Equation (RUSLE). Its direct estimation, however, requires high-temporal-resolution rainfall records to compute the storm erosivity index, EI₃₀, which are available at relatively few locations. This limitation constrains erosion assessment and conservation planning in many regions of Mexico. This study develops and evaluates an empirical methodology to estimate the annual rainfall erosivity factor, R, from more widely available daily rainfall totals. A total of 170,796 storm events recorded at 432 automatic weather stations were analyzed to derive four-parameter nonlinear relationships between daily rainfall depth and storm erosivity. The resulting equations provide site-specific transfer functions that were subsequently applied to 2124 climatological stations for the common period 1965–2006. In addition, a station-based quantitative comparison was conducted at the Cerro Catedral Automatic Weather Station, where a reference annual erosivity series was derived directly from 10 min rainfall records. For this case study, the proposed methodology reproduced the reference annual erosivity series more closely than the regional equations of Cortes, yielding a substantially lower standard error of fit (SEF = 347 MJ·mm·ha⁻¹·h⁻¹·yr⁻¹ versus 1455.77 MJ·mm·ha⁻¹·h⁻¹·yr⁻¹). At the national scale, the resulting erosivity patterns were spatially coherent with the major rainfall gradients of Mexico and supported by a substantially larger observational dataset than previous national formulations. By enabling national-scale erosivity estimation from standard daily rainfall data, the methodology expands the spatial applicability of RUSLE and provides a practical basis for soil erosion assessment, sediment-yield studies, and land and water conservation planning under current and future hydroclimatic pressures.