Wet antecedent soil moisture increases atmospheric river streamflow magnitudes non-linearly

Journal of Hydrometeorology
Desert Research Institute, Reno, NV
By: , and 

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Abstract

Atmospheric rivers (ARs) drive most riverine floods on the United States (U.S.) West Coast. However, estimating flood risk based solely on AR intensity and duration is challenging because precipitation phase, antecedent conditions, and physical watershed characteristics (e.g., slope and soil depth) can influence the magnitude of floods. Here, we analyze how antecedent soil moisture (ASM) conditions contribute to variability in streamflow during AR events and how that changes across climatic regimes and physiography in 122 U.S. West Coast watersheds. We identify a robust non-linear relationship between streamflow and ASM during ARs in 89% of watersheds. The inflection point in this relationship represents a watershed-specific critical ASM threshold, above which event maximum streamflow is, on average, two to four and a half times larger. Wet ASM conditions amplify the hydrologic impacts of more frequent but weaker, lower moisture transport AR events, while dry ASM conditions attenuate the hydrologic impacts that stronger, higher moisture transport AR events could otherwise cause. Our research shows that watersheds prone to ASM-amplified streamflows have higher evaporation ratios, lower cold-season precipitation, lower snow-to-rain ratios, and shallower, clay-rich soils. Higher evaporation and lower precipitation lead to greater ASM variability during the cold season, increasing streamflow during wet periods and buffering streamflow during dry periods. Lower snow fraction and shallower soils limit the antecedent water storage capacity of a watershed, contributing to greater sensitivity of streamflow peaks to ASM variability. Incorporating ASM thresholds into hydrologic models in these regions prone to AR-amplified streamflow could improve forecasts and decrease uncertainty.

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Publication type Article
Publication Subtype Journal Article
Title Wet antecedent soil moisture increases atmospheric river streamflow magnitudes non-linearly
Series title Journal of Hydrometeorology
DOI 10.1175/JHM-D-24-0078.1
Volume 26
Issue 6
Year Published 2025
Language English
Publisher American Meteorological Society
Contributing office(s) Lower Mississippi-Gulf Water Science Center
Description 18 p.
First page 741
Last page 758
Country United States
State California, Nevada, Oregon, Washington
Additional publication details