On the reliability of gamma distributed dsds for modelling kinetic energy of rainfall*

Abstract

AbstractTo retrieve the gamma drop size distribution (DSD) parameters from observed drop spectra, the most common approach is the method of moments (MM). However, the goodness of this method is still disputed. To assess its reliability, the aims of this paper are: (i) estimation of empirical values of rainfall rate (I) and kinetic energy (KE) from DSD measurements collected by a laser‐optical disdrometer; (ii) estimation of gamma DSD parameters by MM and another widespread method, i.e. maximum likelihood (ML); (iii) evaluation of theoretical values of rainfall rate and KE and comparison between these values and measured ones. The novelty of this work is the assessment of both MM and ML using the rainfall intensity measured by the disdrometer as a benchmark, rather than the KE or a statistical test as done in common practice. The assessment of the goodness of the estimates was performed on variables most investigated in soil erosion studies (i.e. I and KE). Results show that smaller error values are associated with ML and that MM does not provide reliable estimations of I. On the other hand, both methods substantially underestimate KE with increasing rainfall intensity.