North American Scale Convection-Permitting Climate Modeling: Mesoscale Convective Systems Under Climate Change

Using a North American scale convection-permitting model (horizontal grid spacing of 4 km) to simulate a current and an end-of-century 13-year long period, we are able to model mesoscale processes on climate time scales. Producing these simulations is challenging because of significant computational costs, large data volume, and the need to develop alternative model evaluation strategies to analyze mesoscale processes over long time periods. In this talk, we will discuss some of these challenges, strategies used to address them, and assess the model's ability to simulate Mesoscale Convective Systems (MCSs) in North America. So far little is known about how MCSs might change due to global warming. Using a storm tracking algorithm we show that the model is able to accurately reproduce the main characteristics of current MCSs, such as their size, propagation speed, maximum rainfall, and total rainfall volume in the present climate. At the end of the century, the number of intense MCSs are projected to more than triple in North America during summer. MCS maximum hourly precipitation rates would increase by 15–40 %, which is in line with theoretical expectations from the Clausius-Clapeyron relationship. In addition, simulated future MCSs increase in size and have larger areas with high rain rates. This results in an increase in MCS total precipitation volume by 30–80 %. This previously unrecognized increase in precipitation volume raises the future flood risk beyond previous expectations.