Changes in Vertical Velocity and Precipitation Mode in Flash Flood-Producing Storms in the Mississippi River Basin in a Future Climate

The Mississippi River Basin (MRB) is a flash flood hotspot in the United States, receiving the most frequent floods and highest rainfall accumulations across the country. In a future warmer climate, this region exhibits some of the greatest increases in rainfall associated with storms that produce flash floods. In order to better understand these future changes, convection-permitting simulations of a current and future climate are utilized to study changes to storm dynamics and precipitation in these convectively-driven flash flood-producing storms. 

First, nearly 500 flash flood-producing storms in the MRB are examined under a pseudo-global warming framework to examine the role of vertical velocity in modulating future rainfall changes. Three different categories of storms are designated based on their vertical velocity magnitude in the current climate–weak, moderate, and strong. While all storm categories display an increase in future rainfall accumulation, the amount of increase varies by the storm’s vertical velocity magnitude, which also changes in the future. 

Second, idealized WRF simulations are run based on a composite sounding of the flash flood-producing storms in the MRB that occurred during the warm season. Future temperature, moisture, and horizontal wind perturbations are added to the initial sounding using the CESM Large Ensemble Data Set under the RCP 8.5 emissions scenario. In these idealized simulations, the contribution of different precipitation modes to future changes in rainfall are examined. The relationship between changes in future precipitation mode and storm dynamics provides a better understanding of how storm processes influence future changes in rainfall in a flash flood prone region in the United States.