Extreme Precipitation Events in Alaska: Historical Trends and Projected Changes

Extreme precipitation events during the summer of 2021 raise questions about how the frequency of extreme flooding will change as the climate changes. While recent increases of heavy precipitation events in some midlatitude regions are consistent with climate model simulations, evidence of such increases in high latitudes is more tenuous, partly because of data limitations. The present study seeks to understand how the frequency of extreme precipitation events have changed and will change in Alaska. Using the ERA-5 reanalysis, station data, and model output (CCSM4 and GFDL CM3), we examine historical trends, end-of-century model projections (2065-2100), and precipitation-driven flood events at five diverse locations in Alaska where major historical floods provide benchmarks: Fairbanks (August, 1967), Seward (October, 1986), Allakaket/Bettles (August, 1994), Kivalina (August, 2012), and Haines (December, 2020). In all but one of these floods, the amount of rainfall was the highest on record for the event duration, and precipitation events of this magnitude are generally projected by the models to remain rare. All cases had subtropical or tropical moisture sources. None of the locations show statistically significant historical trends in the magnitude of extreme precipitation events in ERA-5 or the station data. However, the frequencies of heavy precipitation events are projected to increase at most of the locations. The frequency of events with 2-year and 5-year historical return intervals are projected to increase by factors of about 2 (CCSM4) to about six (GFDL CM3). Decreases are projected only for Seward.