Future Simulated Changes in Central US Mesoscale Convective System Rainfall Caused by Changes in Convective and Stratiform Structure

Mesoscale convective systems (MCSs) are responsible for a majority of warm season flash flood events in the central U.S. Given their high impact, it is critical to understand how MCSs will change in a future climate. This study identifies eight flood-producing MCS cases of different archetypes and runs ensembles of 192 high-resolution historical and future simulations in order to analyze the range in future MCS rainfall and structural changes. Future area-average rainfall increases by 98% on average, with an 89%-111% range among ensemble members, while maximum rainfall increases by 31%, with a 24%-43% range. MCSs components are classified into deep convective cores (DCCs), wide convective cores (WCCs), and broad stratiform regions (BSRs) to understand how changes in these structures contribute to future rainfall changes. In a warmer climate, the number of DCCs increase on average by +30 (+5,545%), the average WCC area increases by 75%, and the average BSR area increases by 40%. The future rainfall increases are mainly due to increases in convective rainfall with large variability in rainfall from DCCs and less variability from WCCs. Despite their increase in size, BSR rainfall shows little increase. These rainfall and structural changes vary among MCS types, with back-building MCSs exhibiting the largest increases in future rainfall mainly due to increases in the number of DCCs and WCC area. Such information is critical to better understand the drivers of change in future MCS rainfall and improve prediction of future flood impacts.

Automated summary

This study identifies different archetypes of flood-producing MCS cases and analyzes the range in future MCS rainfall and structural changes through high-resolution simulations. The results show that future rainfall will increase on average by 98%, with a maximum increase of 31%. The number and size of different components of MCSs contribute differently to the future rainfall changes, with back-building MCSs showing the largest increases.