A 2°C warming can double the frequency of extreme summer downpours in the Alps

Intense short-duration summer rainfall in mountainous areas can trigger a variety of natural hazards, including flash floods, debris flows, and urban floods. Warming is expected to intensify extreme sub-hourly rainfall events in response to an increased atmospheric water vapor content and invigorated storm dynamics. Here, we employ a new physically-based statistical model to estimate the projected intensification of sub-hourly and hourly extreme rainfall across 299 high-mountain Alpine stations in France, Germany, Switzerland, Italy, and Austria. Analyzing the projected intensification for 10-min rainfall at 1 to 3 degrees C of warming confirms a general intensification at a rate of 9% degrees C-1 over the Alpine region, with a stronger intensification at higher elevations. With a 2 degrees C increase in average regional temperature relative to the 1991-2020 period, extreme rainfall statistics over the Alps are likely to undergo significant changes, resulting in a two-fold increase in the probability of occurrence of the extreme rainfall levels used for infrastructure design and risk management.