Measurement Method of Rainfall Energetic Characteristics Applying the Weibull Drop Size Distribution

Abstract

Rainfall kinetic energy is the most used variable to represent rainfall erosivity, that is the attitude of rainfall to erode soil. Accurate measurements of rainfall erosivity are useful for a reliable prediction of soil loss, and thus to develop a reliable prediction model of the erosive phenomenon. Currently, the rainfall energy can be derived from knowledge of the raindrop size distribution (DSD) and the raindrop falling velocity. Disdrometer measurements require the detection of a high amount of numerical data that is difficult to elaborate and manage remotely. Moreover, considering the relevant installation and management costs, disdrometers are unsuitable for impact energy detection at a large spatial scale, and their use is mainly limited to experimental installations for scientific research. Recently, an innovative method and its advances to measure rainfall energy, subject to a patent, have been proposed. This method is based on the simultaneous detection, in a given time interval, of the rainfall intensity and the number of raindrops that hits a specific surface. In this paper, a theoretical analysis aimed at improving the reliability of this rainfall energy measurement is firstly presented. The developed analysis accounts for the detection of a further variable deriving from the momentum distribution. Then, the reliability of the proposed approach was tested using more than 5500 DSDs recorded at El Teularet (Spain) in the period 2016-2017. The analysis showed that the use of the proposed approach yielded to have accurate estimation of the rainfall kinetic power. Therefore, the use of the proposed approach will allow for improving the reliability of the rainfall kinetic power measurement at large spatial scale.