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A new study, “The Occurrence of Large Floods in the United States in the Modern Hydroclimate Regime: Seasonality, Trends, and Large-Scale Climate Associations,” evaluates changes in the number of large river floods across the United States over a recent 50-year period. It includes the first detailed characterization of large-flood seasonality.

The study team, led by Mathias Collins (National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Gloucester, Massachusetts) and including Glenn Hodgkins (U.S. Geological Survey [USGS] New England Water Science Center) and Stacey Archfield and Robert Hirsch (USGS Water Resources Mission Area), found little evidence that large floods have become more or less frequent from 1966 to 2015, but they did find some regional and national relations between large-flood occurrence and known climate patterns such as the Pacific North American pattern.

They found that large-flood seasonality is strong in some regions but is weak or complex in other regions, where floods have a variety of causes. The latter is true in the Northeast United States, where flood-rich months included January, March, April, June, and September.

There were insignificant increases in the annual number of large floods in the Northeast during the last 50 years.

Ducktrap River, Maine, April 2005
Streamflow in the Ducktrap River, coastal Maine, showing typical spring high flow in April 2005. 

 

Trends in the number of large flood events from 1966 to 2015 for 14 regions of the United States
Trends in the number of large flood events from 1966 to 2015 for each of 14 regions of the United States. Shaded areas are 95-percent confidence intervals. 
 

 

Reference

Collins, M.J., Hodgkins, G.A., Archfield, S.A., and Hirsch, R.M., 2022, The occurrence of large floods in the United States in the modern hydroclimate regime—Seasonality, trends, and large-scale climate associations: Water Resources Research, v. 58, no. 2, 22 p.,  https://doi.org/10.1029/2021WR030480.