Dual atmospheric controls amplify streamflow extremes in Alabama

Abstract The Southeastern United States (US) has experienced increased population growth and urbanization in recent decades, highlighting the importance of water management and availability. The Black Warrior River basin is in an area with an increasing precipitation trend and no previous streamflow reconstruction. To contextualize current streamflow, we reconstructed over 400 years (1550–2023 CE) of May–July (MJJ) streamflow for the Black Warrior using 10 tree ring chronologies, including a new 36-core bald cypress ( Taxodium distichum ) chronology. Flows >2000 m 3 s −1 occurred in <5% of years, with 90% of years exceeding 200–300 m 3 s −1 . While central flow quantiles showed little long-term trend, upper quantiles (⩾0.90) had strong positive slopes while lower quantiles (⩽0.10) trended slightly downward, demonstrating an increased variance driven by extremes occurring in the last 40 years (beginning in the late 20th century). Our results show that five of the highest MJJ flow years of the reconstruction occurred within the last 40 years, with 1989, 1997, and 2021 all in the 99th percentile of high flow years. These recent extreme flow years reflect the influence of both tropical cyclones (TC) and frontal precipitation, an example of which is 2021 with two intense frontal precipitation events (May 4, ∼108 mm; July 19, ∼55 mm) and a TC (Claudette; ∼110 mm). Correlations show a linkage between increased meridional and zonal wind stress (300 hPa) and decreased geopotential height (500 hPa) with higher flows, consistent with a wavier, southward-displaced North Atlantic Jet (NAJ). Combined with documented increases in TC precipitation in the eastern U.S., our findings emphasize that these widely documented NAJ-driven changes have amplified Black Warrior MJJ streamflow and variability.