RAINFALL KINETIC ENERGY IN THE SONORAN AND CHIHUAHUAN DESERTS

The Sonoran and Chihuahuan Deserts are exemplary regions showcasing the impacts that rainfall has on landscape erosional processes. These two neighboring deserts share a common bimodal rainfall regime marked by maxima during the summer (July-September) and winter (November-March) seasons. A large portion of rainfall is delivered during the North American Monsoon in high-intensity, short-duration events that leads to significant runoff generation producing hydrologic and geologic hazards. Rainfall-induced erosive processes typically begin with the initial breakdown and transport of surface material that is directly related to the rainfall drop size and velocity distribution (DSVD) from individual storm events. In this work, DSVD data is collected from two locations in the Sonoran (Mesa, AZ) and Chihuahuan (Las Cruces, NM) Deserts using the Parsivel²optical disdrometer, each deployed in a consistent fashion and within the context of hillslope runoff and erosion experiments (an experimental facility at Mesa, AZ, and natural runoff plots at Las Cruces, NM). Individual rainfall drops are binned into one of 32 size/velocities classes collected from an effective area of 54 cm²at roughly 2 m from the soil surface. After characterizing the DSVDs and the potential for the control by three-dimensional wind speed, we estimate the rainfall kinetic energy (KE) as each droplet strikes the soil surface. Preliminary analyses of the DSVDs for a select set of storms highlight the variability between events leading to significant differences in KE rate despite similar rainfall intensity. These measures improve current knowledge regarding rainfall characteristics as compared to more commonly-applied metrics such as rainfall intensity, obtained from two different types of rainfall gauges at each site (tipping bucket and siphoning, tipping bucket). Our comparisons for events from winter 2018 through summer 2019 in both regions provide insights into the variation of the erosive potential of individual rainfall events for the bimodal precipitation regime in the southwestern United States.