High and dry: A ∼300-year record of hydrologic extremes from the French Broad River in the southeastern U.S.

Abstract

Study region

French Broad River Basin, southeastern United States

Study focus

We combined fluvial and dendro-based paleoflood hydrologic data with instrumented data to understand long-term changes in extreme flow events.

New hydrological insights for the region

Droughts and extreme floods are underrepresented in streamflow records because of short instrumentation records. This study is among the first to develop a centennial-scale record (1734–2024) of hydrologic extreme events in the southeastern U.S. Interannual and interdecadal variability of extreme floods and droughts was observed. This suggests that hydrologic volatility is a persistent pattern in basins where precipitation is heavily influenced by the Bermuda High (North Atlantic subtropical high) and El Niño Southern Oscillation. Landfalling hurricanes generated some of the largest floods in the record. A late spring flood in 1791 CE, however, surpassed the magnitude of all other floods (0.0025 annual exceedance probability), including the 2024 CE Hurricane Helene flood (0.02 annual exceedance probability). Flood frequency and magnitude has declined since the 1800s, however. In contrast, drought severity has increased in the last century. Taken as a whole, these findings suggest flood frequency analyses reliant on floods-of-record from the last century to represent flood extremes may be underestimating flood risks, and droughts and extreme floods both occur on annual and decadal timescales, setting the stage for frequent sequencing of hydrologic extremes in the southeastern U.S.