Abrupt Climate Change and Flood Response in the Tennessee River Valley, Tennessee (USA)

Keywords: Extreme floods; Climate Change; Holocene; Paleofloods
Session Type: Virtual Paper Abstract
Day: Friday
Session Start / End Time: 2/25/2022 08:00 AM (Eastern Time (US & Canada)) - 2/25/2022 09:20 AM (Eastern Time (US & Canada))
Room: Virtual 19

Abstract

Extreme floods, with multi-century to millennia recurrence intervals, arise from a combination of antecedent watershed characteristics and unusual or rare atmospheric circulations that occur too infrequently to discern from instrumented records. Few stream gauge records in the United States contain 100 years or more of annual peak flow data, meaning rare extreme floods are underrepresented in the peak flow population. We synthesized 8000-years of paleoflood hydrologic data from multiple studies and various landforms (floodplains, rock shelters, and caves) conducted in the Tennessee River Valley between Chattanooga, Tennessee, and Florence, Alabama, to examine Holocene flood variability. Extreme floods (>110,000 m3/s) clustered around ~7900, 6000-5000, and ~1000-80 cal yrs BP. More moderate floods occurred between 5000 and 2000 cal yrs BP. We compared flood variability in the Tennessee Valley to Holocene paleorecords available for the southeastern US and mid-latitude North America. All periods of extreme flooding occurred during large-scale, abrupt climate transitions lacking a distinct directionality of temperature change (i.e., warm to cool or cool to warm). These results suggest extreme floods may be associated with abrupt hydroclimate shifts within a river basin. Significantly, episodes of drought occurred before most of the extreme floods, and the moderate flood period lacked sustained droughts. Patterns of drought followed by extreme floods during shifts in precipitation regimes suggest extreme flood magnitude may be amplified by drought altering watershed conditions prior to the shift. These findings suggest that anticipated changes to drought and precipitation intensity due to modern climate change would increase extreme floods.