Changes in Flash Flood-Producing Storms in the U.S.

Floods are one of the deadliest natural disasters in the continental United States (CONUS), with the spring 2019 floods in the Mississippi River Valley resulting in an estimated $12.5 billion in damage alone. Given their highly destructive nature, it is important to understand how floods will change in a future, warmer climate. Previous studies using global climate models have examined this topic and find that flood risk increases in the future, but these models are too coarse to accurately simulate precipitation timing, structure, and intensity. While high-resolution convection-permitting climate models improve simulations of current and future rainfall, they have not yet been explicitly used to understand changes to future floods. Thus, the goal of this research is to fill this knowledge gap by using high-resolution convection-permitting regional climate simulations that apply a pseudo-global warming approach to analyze how flash flood-producing storms will change in a future climate over the CONUS. Changes in historical flash flood-producing storm rainfall characteristics are examined in current and future simulations, using 584 cases from a flood-producing storm climatology. Flash flood rainfall increases over most of the CONUS in a future climate, with increases in maximum rain rates exceeding that predicted by Clausius-Clapyeron theory. To understand the physical processes of why future flash flood-producing storms intensify, we perform a regional analysis in the Mississippi River Valley–a flash flood hotspot in the CONUS–and examine how the storm characteristics and associated connections to hydrology might change in a future climate.