The relationship between potentially erosive storm energy and daily rainfall quantity in England and Wales.

Erosive storm energy is the primary driver of soil detachment, and hence a major determinant of transfer of sediment and particulate phosphorus (P) to surface waters. Modelling of sediment and P loss at catchment scale, for example for the development of catchment and national mitigation policies, requires a spatially interpolated estimate of variation in erosion risk. To this end we present a method of estimating total rainfall erosivity, as kinetic energy (KE), for any location in England and Wales, from daily rainfall data or monthly climate data. Analysis of detailed, high-resolution records from eleven contrasting sites showed strong predictive correlations between daily rainfall quantity and associated daily total kinetic energy estimated from hourly rainfall intensities. The coefficients showed systematic seasonal variation, with greatest KE per unit of rainfall in late summer and autumn months. In contrast, no systematic spatial variation was found as a function of location or continentality index. The relationships were integrated with probability distributions of rainfall quantity per rain day derived from spatial climate data (monthly rainfall totals and numbers of rain days). The resulting map captures and quantifies the effects of rainfall quantity and intensity patterns on risk of sediment detachment, and as such provides a critical input layer to catchment-scale models of sediment and P transfer.