Global hotspots of large precipitation extremes

Abstract Spatial footprint, that is, the length scale of precipitation extremes, directly impacts the affected area and flooding [1, 2]. However, a physical framework for analyzing it has yet to be developed. Here, we investigate the seasonal and spatial distribution of the spatial footprint of precipitation extremes, their observed changes, and the underlying physical processes using the observational records of the last four decades. We show that subtropical arid regions are global hotspots for large-scale precipitation extremes, which are triggered mainly by the breaking of planetary-scale waves. The eddy length scales measure the spatial scales at which the weather systems are most prevalent. In the extratropics (poleward of 30◦ N/S), the eddy length scales exhibit a significant positive correlation with the length scale of precipitation extremes. Our analysis indicates that the eddy length scales offer a useful framework to assess the spatial footprint of precipitation extremes in the extratropics. Although precipitation is scarce in arid regions, sudden deluges with large spatial footprints over just a few hours to days can make them highly vulnerable to flash floods. We emphasize that the frameworks for design rainfall estimation [3–5] should account for the spatial footprint of events in addition to the conventional characteristics of intensity, duration, and frequency.