On Two Definitions for Precipitation Intensity: Differences, Artifacts, and Ambiguities

Abstract The correct quantification of precipitation intensity is crucial over arid and semiarid regions, as it impacts the environment and infrastructure via different processes such as soil erosion, flooding, and landslides. In this study, we use global, gridded precipitation from reanalyses and satellite- and gauge-derived products to assess the differences arising from two widely used precipitation intensity definitions, namely: I = P / F wet (where P is the average daily precipitation rate over the entire analysis period and F wet is the frequency of occurrence of wet days, defined as days with accumulations of at least 1 mm) and I wet (computed as the precipitation rate averaged over wet days only). We show that I > I wet and that the relative difference between the two definitions scales with the inverse of F wet . Over semiarid regions, the I metric typically inflates values by at least 10% compared to I wet , whereas over arid ones, the difference can exceed 100%. Furthermore, singularities were found as I may become larger than the climatological extreme (but not I wet ). By evaluating the relative change in intensity from two adjacent 20-yr periods, we also found that the sign of the change can be different if I is used instead of I wet . For very arid regions, wet days defined as rates > 1 mm may account for smaller precipitation accumulations than “dry” (