Estimation of rain kinetic energy from radar reflectivity and/or rain rate based on a scaling formulation of the raindrop size distribution

This study offers an approach to estimate the rainfall kinetic energy (KE) by rain intensity ( R ) and radar reflectivity factor ( Z ) separately or jointly on the basis of a one‐ or two‐moment scaled raindrop size distribution (DSD) formulation, which contains (1) R and/or Z observations and (2) the dimensionless probability density function (pdf) of a scaled raindrop diameter. The key point is to explain all variability of the DSD by the evolution of the explaining moments ( R and Z ); hence the pdf is considered as constant. A robust method is proposed to estimate the climatological values of the parameters with a 28 month DSD data set collected in the Cévennes‐Vivarais region of France. Three relationships (KE‐ R , KE‐ Z , and KE‐ RZ ), which link the observations ( R and/or Z ) to rainfall kinetic energy (KE), are established. As expected, the assessment using the disdrometer data indicates that (1) because of the proximity of the moment orders, the KE‐ Z relationship exhibits less variability than the KE‐ R relationship and (2) the combination of R and Z yields a significant improvement of the estimation of KE compared to the single‐moment formulations. Subsequently, a first attempt to spatialize the kinetic energy using radar and rain gauge measurements is presented for a convective event, showing a promising potential for erosion process studies. Different from the application with the disdrometer data, the performance of the KE‐ Z relationship degrades compared to the KE‐ R relationship as a result of a bias and/or the sampling characteristics of the radar data.