Rainfall drop arrival rate at the ground: A potentially informative parameter in the experimental study of infiltration, soil erosion, and related land surface processes

Abstract

Rainfall drop arrival rate (DAR) quantifies the number of impacts at the ground of drops of varying size per unit area and time. It can be calculated from the drop size distribution and fall speed data used for rain integral parameters such as total kinetic energy or rainfall intensity. However, the DAR can also be calculated for individual drop size classes, revealing the relative number of impacts of small and large drops. New calculations of DAR are developed, and show that for increasingly intense rain, impacts by drops of large diameters become more common, and contribute an increasing proportion of the total kinetic energy. This may exert an important influence on many landsurface processes. A comparison with the kinds of rainfall arrival rates present in simulated rainfall is made, and suggests that although simulated rainfall may be generated with an intensity corresponding to natural rain, the DAR, especially for small and large drops, is often significantly different to the value expected in natural rain. For research on soil splash, interrill erosion, infiltration, and other important land surface processes, it is suggested that attention to DAR may prove informative, both as a potentially useful explanatory variable in field studies made under natural rainfall, and as a target parameter in the design of rainfall simulation experiments.