Estimation of rainfall erosivity using 5- to 60-minute fixed-interval rainfall data from China

The 30-min rainfall erosivity index (EI30) is commonly used in the Universal Soil Loss Equation for predicting soil loss from agricultural hillslopes. EI30 is calculated from the total kinetic energy and the maximum 30-min rainfall intensity of a storm. Normally, EI30 values are calculated from breakpoint rainfall information taken from continuous recording rain gauge charts, however, in many places in China and other parts of the world the detailed chart-recorded rain gauge data relative to storm intensities are not readily available, while hourly rainfall is readily available. The objective of this study was to assess the accuracy of EI30 estimations based on 5-, 10-, 15-, 30-, and 60-min time-resolution rainfall data as compared to EI30 estimations from breakpoint rainfall information. 456 storm events from five soil conservation stations in eastern China were used. The values of EI30 based on the fixed-time-interval data were less than those calculated from breakpoint data. The average conversion factors (ratio of values calculated from the breakpoint data to those from the fixed-interval data) for the five stations decreased from 1.105 to 1.009 for the estimation of E values, from 1.668 to 1.007 for I30 values, and from 1.730 to 1.014 for EI30 values as the time resolution increased from 60 to 5 min. The maximum 30-min rainfall intensity was the major source of error in estimating EI30 for 60-min fixed-interval data, while storm kinetic energy played a proportionately more significant role as the fixed-interval data decreased from 60 to 5 min.