Analysis of the relationship between the kinetic energy and intensity of rainfall in Daejeon, Korea

Abstract

The kinetic energy and momentum of rainfall are widely used as erosivity indicators for estimating soil detachment (erosion) induced by the impact of raindrops. Because direct measurements of the force or kinetic energy of rainfall on ground surfaces are not widely available, many empirical relationships have been derived to link the kinetic energy and intensity (I) of rainfall, the factor that has the most control over soil erosion and is readily accessible. This study considered three rainfall erosivity indices: kinetic energy expenditure (KEtime, J m−2 h−1), kinetic energy content (KEmm, J m−2 mm−1), and momentum (M, kg m s−1 m−2 s−1 or N m−2). The relationships between these rainfall erosivity indices (KEtime, KEmm, and M) and rainfall intensity were established by fitting to an existing functional model based on measurements of the number of drops by size and terminal velocity made from January 2010 to July 2011 using a laser optical disdrometer in Daejeon City, Korea. The best fit for the relationship between the three kinetic energy indices and rainfall intensity was obtained with a power law (KEtime-I, and M−I) and an exponential model (KEmm-I). Validation results for two different events indicated good performance for the KEtime-I and M−I equations, with a similar distribution of observed data and power-law curve fitting. However, the rainfall momentum index produced much lower uncertainty as determined from the measured terminal velocity when the equipment was exposed to in situ changeable conditions. Therefore, we suggest that the power-law relationship between momentum and rainfall intensity is the most suitable equation for the prediction of rainfall erosivity.