Storylines of Unprecedented Extreme Weather

If our disaster preparedness systems continue to rely on historical events for contingency planning, they will continue to be surprised by events that are possible in today’s changed climate. In collaboration with American Red Cross and NASA, we identified five US counties that are working on disaster preparedness in a changing climate. We use the Unprecedented Simulated Extremes using Ensembles (UNSEEN) approach to identify storylines of plausible extreme weather events in these six counties that have never occurred, but events are physically plausible in today's climate. To create a multi-model large ensemble, we use the archives of ECMWF SEAS5 forecasts and NASA GEOS forecasts, evaluated for stability and independence across leadtimes and fidelity against Daymet observations. In the five selected counties in Louisiana, California, Alabama, Kentucky, and Mississippi, we present the change in return periods of extreme heat and extreme rainfall events between 1980 and 2022. We then use these models to describe scenarios of physically plausible but as-yet-unprecedented disasters that can be used for disaster preparedness planning, and we summarize the joint science-policy scenario workshops that we have held with American Red Cross using this data.