Effect of Wind on Precipitation Intercepted by Steep Mountain Slopes

A simple and efficient formulation is developed to describe the effects of wind speed and direction on ground level precipitation intercepted by steep mountain slopes. A 3D rainfall field is reproduced from measurements of (vertical) precipitation intensity, wind speed, and wind direction. The Marshall-Palmer drop size distribution is used to express the volumetric precipitation water content as a function of measured precipitation intensity, and raindrops are assumed to move horizontally with the measured wind speed and direction. Land topography is described using digital elevation model data, and local contributions to ground level precipitation are calculated as the interception of the obtained 3D rainfall field by horizontal and vertical surfaces that constitute the elemental land surface systems. The developed formulation is tested at the Acquabona and Fiames mountain slopes, located in the Northern Italian Dolomites, near the town of Cortina dʹAmpezzo, where debris flow phenomena often occur. Simulation results are corroborated, although in an indirect and approximate manner, by field estimates of debris flow volumes delivered by the considered mountain slopes in response to monitored storm events. Although more accurate and comprehensive validation is needed, the developed formulation appears to constitute a useful diagnostic tool for providing interpretation of storm-flow hydrographs delivered by steep mountain slopes in response to storm precipitations affected by wind.