Development of isoerodent maps for Nigeria from daily rainfall amount

In this study, rainfall erosivity factor, R. of the Revised Universal Soil Loss Equation (RUSLE) was estimated from daily rainfall amounts of the coastal, humid forest, savanna, semi-arid and arid zones of Nigeria using data from 17 locations, which spanned 10-33 years. Two power law equations were applied to compute the products of kinetic energy, e, and (i) maximum 30-minute intensity, I(30) (EI(30)), and (ii) maximum 15-minute intensity, I(15) (EI(15)). The indices were used to develop monthly and annual isoerodent maps. Mean monthly EI(30) ranged from 600 to 3200 MJ mm ha(-1) h(-1) whereas the annual values ranged from 3000 to 27,000 MJ mm ha(-1) h(-1) from the arid to the coastal zones. The EI(15) index was 1.7 times greater than the EI(30). Trends of rainfall erosivity in the derived, southern Guinea and northern Guinea savannas or wet savannas were erratic and less predictable from the trends of rainfall amount, unlike in the coastal, humid forest, semi-arid and arid zones. Extrapolation of data for soil conservation planning did not appear feasible in the wet savannas. Monthly values of erosivity presented are recommended for conservation plans during the cropping seasons in the various agroecological zones. The EI(15) index is recommended for both monthly (seasonal) and annual soil loss computations because short-term intensities reveal rainfall erosivity better in the tropics. (C) 2010 Elsevier B.V. All rights reserved.