Sensitivity of historical orographically enhanced extreme precipitation events to idealized temperature perturbations

Abstract

Using high resolution convective permitting simulations, we have investigated the sensitivity of historical orographically enhanced extreme precipitation events to idealized temperature perturbations. Our simulations were typical autumn and winter synoptic scale extreme precipitation events on the west coast of Norway. The response in daily mean precipitation was around 5%/K for a 2 °C temperature perturbation with a clear topographical pattern. Low lying coastal regions experienced relative changes that were only about 1/3 of the changes at higher elevations. The largest changes were seen in the highest elevations of the near coastal mountain regions where the change was in order of +7.5%/K. With a response around 5%/K, our simulations had a precipitation response that was around 2%/K lower than Clausius-Clapeyron scaling and 3%/K lower than the water vapor change. The below Clausius-Clapeyron scaling in precipitation could not be explained by changes in vertical velocities, stability or relative humidity. We suggest that the lower response in precipitation is a result of a shift from the more efficient ice-phase precipitation growth to less effective rain production in a warmer atmosphere. A considerable change in precipitation phase was seen with a mean increase in rainfall of 16%/K which was partly compensated by a reduction in snowfall of around 23%/K. This change may have serious implications for flooding and geohazards.