Rainfall drop size distribution in the Western Mediterranean basin, València, Spain

Abstract

Although soil erosion processes are directly related to the raindrop sizes and the kinetic energy of the rainfall, little is known about the drop-size distribution. The paper staining technique is used to measure the size of the raindrops for natural thunderstorms with different rainfall intensities in the Western Mediterranean basin (Canals and Valencia, Spain). Drop sizes are greater during the most intense thunderstorms, ranging from 0.25 mm diameter ( D 50 ) for a 1 mm h −1 rainshower to 2.69 mm in very intense thunderstorms of about 120 mm h −1. The shape of the raindrop size distribution curve changes from lower to higher rainfall intensity thunderstorms. For the low intensity events, the raindrops are very small and most of the rain falls in four to five drop size classes (from 0 to 0.5 mm). In contrast, the raindrops are larger in the higher rainfall intensity events. For the most intense thunderstorms there are 62 size classes ranging from 0 to 3.87 mm. No raindrops larger than 4 mm were found during the seven months of measurements. In comparison with other reported measurements, the drop-sizes in the Western Mediterranean basin are smaller for rainfall intensities lower than 100 mm h'. Nevertheless, for higher rainfall intensities the raindrop size distributions are similar to those measured in Central United States since 1940.