Changes in the Past and Future Extreme Precipitation within the Eastern United States Using Long Observation Record and Dynamically Downscaled Simulations from 2025 to 2100

The increasing trend in the frequency and intensity of extreme precipitation events has been well-documented within the eastern United States using the historical climate records. The flooding associated with extreme precipitation imposes unprecedented challenges to affected communities. Studies also describe dramatic ecosystem responses to extreme events with a plausible regime shifts in the intensity and quantity of runoff within some watersheds. Furthermore, climate models indicate that precipitation intensification will continue to increase throughout the twenty-first century.

This study presents analyses of the trends in 30-year normals of annual and seasonal extreme precipitation for 10 sites in the Eastern U.S., based on the available daily precipitation observational data from last 120 to 148 years. Analysis of daily precipitation allow detection of internal climate variability and emerging trends. These results are compared with simulated precipitation extremes (2025-2100) generated using the Weather Research and Forecasting (WRF) model to dynamically downscale simulations from two global climate models for the highest greenhouse gas emission scenario (RCP8.5): the Community Earth System Model (CESM) and the Geophysical Fluid Dynamics Laboratory coupled climate model (CM3).

The observed and modeled trends show spatial variability in the precipitation intensification. In the southeast U.S., trends in the long observation data indicate the presence of multidecadal climate variability in precipitation intensity, which may counteract the increasing tendency in precipitation intensification. Preliminary analyses from the dynamically downscaled simulations indicate up to a 30% increase in the annual maximum precipitation from 2025 to 2100 and an increased variability in the intensity and frequency of the extreme precipitation. Changes in the intensity of extreme precipitation events are more pronounced in the future climate under the RCP8.5, than in the observational record, doubling the intensity of one-day precipitation maxima. However, characteristics of multidecadal variability are less pronounced in the downscaled simulations. Absence of the multidecadal variability maybe an indication of the climate shift or it reveals the inability of the global climate models to capture multidecadal features. This poses a new challenge for the climate science community.