Rainfall erosivity mapping for Santiago Island, Cape Verde

Abstract

Erosivity, the potential of rainfall to detach soil particles, is a parameter used in several models to link rainfall and soil losses. Erosivity is usually calculated from high temporal resolution rainfall during a long period of time, and data is not always available. For Cape Verde, off the west coast of Africa, where data is limited, researchers have calculated erosivity using 7year precipitation data at 15min time interval and using rainfall kinetic energy–intensity relationships developed for temperate areas. In this paper, using additional data collected with an optical disdrometer between 2008 and 2010 with a temporal resolution of 3min, storm erosivity (EI30) was re-evaluated using a new rainfall kinetic energy–intensity relationship developed for Cape Verde. A new equation for storm erosivity as a function of daily rainfall was developed. Annual erosivity R-factor resulting from adding EI30 values was correlated to annual precipitation and to the Modified Fournier Index, calculated from long term monthly data available in Cape Verde. Monthly and long term annual erosivity were mapped using the Modified Fournier Index, and the erosivity R-factor as a function of annual precipitation was mapped for a dry, a wet and an average year. Annual erosivity R-factor in Cape Verde can reach values above 1700Jmmm−2h−1. Given the strong relationship between rainfall and elevation, high erosivity in Santiago Island occurs on higher elevations, coinciding with steep slopes and shallow soils, which makes these areas susceptible to erosion.