Hydrologic Impact of Landfalling Tropical Cyclones in a Changing Climate

Freshwater flooding makes up over half of the fatalities associated with landfalling hurricanes in the U.S., and produces tens of billions of dollars in damages. It is well known that a warming climate is expected to increase the amount of rainfall produced in landfalling hurricanes, though the relationship between rainfall and flooding is more complex. This study explores changes in hurricane flood risk under climate change. It is important to understand the flood risk that may lie ahead, in efforts to improve warning messaging, reduce loss of life, and make communities more resilient.

We used the NOAA National Water Model v2.1 (NWM) configuration of the WRF-Hydro community hydrologic modeling system to simulate hydrologic response to 3 tropical cyclones under historical and future climate conditions. Atmospheric forcings from a pair of 4-km resolution WRF simulations were first regridded to the NWM/WRF-Hydro 1-km resolution land model grid. Hydrologic model "warm starts" at the start of each event were taken from the long-term 42-year NWMv2.1 retrospective. Each event was then simulated using the hydrologic model forced by WRF hourly estimates of precipitation, 2-m air temperature, shortwave and longwave radiation, humidity, surface pressure, and u- and v-component 10-m wind speeds. Changes in flood hazard will be presented through an analysis of streamflow metrics. We will also compare these results to model simulated rainfall.