Representing Uncertainty of Future Extreme Rainfall Events Using a WRF Precipitation Ensemble

Extreme precipitation will change in a future climate impacting flooding potential. There is uncertainty in how extreme precipitation will change in the future and this presents a problem for hydrological models, which are forced by precipitation. To better understand the variability and uncertainty of extreme precipitation, we develop an ensemble of weather research and forecasting (WRF) model simulations to forecast precipitation for extreme rainfall events in the past 30 years. An ensemble approach allows for a range of outcomes given the initial conditions prior to an extreme rainfall event. Once such an ensemble is developed, the ensemble members can be used to force a hydrological model, allowing for quantification of uncertainty in flooding potential. Preliminary development of our ensemble involves comparing simulations using 1 km and 3 km horizontal grid spacing. We find that simulations using 3 km horizontal grid spacing perform similarly to those using 1 km grid spacing. Ensemble performance for a few cases is presented. Future work includes using a pseudo global warming approach to investigate how extreme rainfall and extreme rainfall variability in the ensemble may change in a future climate. A hydrological model will be forced with our pseudo global warming ensemble.