Further Probing the Mechanisms Driving Regional Projections of Extreme Precipitation Intensity

Regional projections of extreme precipitation intensity (EPI) are strongly influenced by regional projections of extreme ascent,. Earlier studies are suggesting that long-term changes in eddy length and vertical stability are key factors influencing extreme ascent projections. We performed controlled experiments using the System for Atmospheric Modeling (SAM). Domains we chosen in the subtropical South Atlantic, where the Canadian Earth System Model version 2 (CanESM2) projects weakening of extreme ascent. SAM was forced with large-scale temperature, moisture and winds from CanESM2 during extreme events in the historical (1981-2000) and future (2081-2100) periods. SAM qualitatively reproduced CanESM2s projected changes in EPI. To gain further insight into physical mechanisms, we performed isolation runs in which some of the CRMs large-scale forcings were changed to their future values, while keeping all other forcings fixed to historical values. In all cases, long-term changes in horizontal advection were the dominant driver of projected decreases in EPI.