Atmospheric rivers are a common cause of flooding on the West Coast of the U.S., but they also bring essential moisture to the region. A recent study has delved into decades of these storms to identify the factors that contribute to catastrophic flooding. By analyzing over 43,000 atmospheric river storms across 122 watersheds on the West Coast between 1980 and 2023, researchers discovered that wet soils are a significant driver of flooding. Flood peaks were found to be 2-4.5 times higher when soils were already saturated, shedding light on why some storms lead to severe flooding while others do not.

The study, published in the Journal of Hydrometeorology on June 4, emphasized that the impact of flooding is not solely determined by the size and intensity of the storm, but also by the conditions on the ground. Lead author Mariana Webb highlighted the importance of pre-event soil moisture in moderating flood events, noting that flood magnitudes do not increase linearly with soil wetness. The study also identified regions where soil moisture has a more significant influence on flooding, such as arid areas like California and southwestern Oregon.

While soil moisture data is currently limited compared to rainfall measurements, the study suggests that increased monitoring in high-risk watersheds could enhance early warning systems and flood management. By tailoring flood risk evaluations to specific watershed characteristics and climate conditions, the research aims to improve flood-risk predictions and integrate land surface conditions into impact assessments for atmospheric rivers.

Webb collaborated with DRI ecohydrologist Christine Albano on this research, which builds on Albano's expertise in studying atmospheric rivers and their impacts. The study's findings could help bridge the gap between atmospheric science and hydrology, offering insights into how these fields can be better connected to improve flood predictions and early warning systems.

Reference: Webb MJ, Albano CM, Harpold AA, et al. Wet antecedent soil moisture increases atmospheric river streamflow magnitudes nonlinearly. J. Hydrometeor. 2025. doi:10.1175/JHM-D-24-0078.1.

Source: Technology Networks