Evaluating and modeling a rainfall kinetic energy and erosivity: a case study of a humid watershed in the Ethiopian highlands

Erosivity is an important component in soil erosion modeling, and it is highly influenced by the kinetic energy of raindrops. However, little research has been conducted on the characterizing and modeling of the kinetic energy and erosivity of rainfall events using measured drop size and velocity in the highlands of Ethiopia. The aim of this study was to evaluate and model rainfall kinetic energy and erosivity in a humid highland watershed (Guder) in Ethiopia. In this study, 1-min rainfall data were recorded with an optical disdrometer for 52 rainfall events from June to October 2022. Regression analyses using linear, power, logarithmic and polynomial functions were employed for 52 rainfall events to established model of kinetic energy and erosivity from commonly available rainfall data (intensity and depth). The result revealed that the volume-based kinetic energy (KEvol) and time-based kinetic energy (KEtime) values of events in the Guder watershed varied from 7.65 to 30.96 J m−2 mm−1 and 32.66 to 1562.94 J m−2 h−1, respectively. A polynomial function (R2 = 0.75, n = 52) was found to be the best fit between KEvol and I, followed by a logarithmic function (R2 = 0.70), whereas the best fit for KEtime was a power function (R2 = 0.76). The potential rainfall erosivity of events was estimated to be 0.96–155.67 MJ mm ha−1 h−1, with an annual value of 1502.74 MJ mm ha−1 h−1. The power function showed a better correspondence with the association between erosivity and rainfall depth (R2 = 0.73) and kinetic energy (R2 = 0.89). Thus, the established models will contribute to estimate the basic rainfall parameters such as KE and erosivity from readily available rainfall data (I and depth) for similar geographical and rainfall characteristics. Additionally, the study contributes for science as input to develop event based soil erosion modeling.