Scientists reveal the hidden trigger behind massive floods
Scientists reveal the hidden trigger behind massive floods
Atmospheric rivers, while vital for replenishing water on the U.S. West Coast, are also the leading cause of floods though storm size alone doesn t dictate their danger. A groundbreaking study analyzing over 43,000 storms across four decades found that pre-existing soil moisture is a critical factor...
Atmospheric rivers, while vital for replenishing water on the U.S. West Coast, are also the leading cause of floods though storm size alone doesn't dictate their danger. A groundbreaking study analyzing over 43,000 storms across four decades found that pre-existing soil moisture is a critical factor, with flood peaks multiplying when the ground is already saturated.
archived (Wayback Machine)
https://journals.ametsoc.org/view/journals/hydr/26/6/hydr.26.issue-6.xml
https://journals.ametsoc.org/view/journals/hydr/26/6/JHM-D-24-0078.1.xml
Antecedent hydrologic storage plays a pivotal role in determining the responsiveness of hydrological systems to precipitation. As lakes, reservoirs, rivers, soils, and aquifers fill, less storage is available, resulting in more runoff and streamflow.
The soil column can comprise a large proportion of the available hydrologic storage space within a watershed, and the volume of this storage is determined by the size of the watershed, the depth and porosity of soils, and how much of that space is already filled with water.
Under wet antecedent soil moisture (ASM) conditions, the likelihood of surface and subsurface runoff increases, in the former case due to saturated soils and in the latter case due to increased hydraulic conductivity of soils (Hillel 2003).
The effects of ASM conditions on streamflow generation have been demonstrated across much of the United States (Berghuijs et al. 2016; Wu et al. 2021), Europe (Berghuijs et al. 2019; Massari et al. 2023), Africa (Tramblay et al. 2021), China (Ran et al. 2022), and India (Garg and Mishra 2019).
For example, during wet ASM conditions in the contiguous United States, extreme discharge is 6 times more likely following extreme precipitation compared to the same precipitation in dry ASM conditions (Ivancic and Shaw 2015).
Conversely, dry antecedent conditions can attenuate flooding by storing incident precipitation and preventing rapid runoff (Sharma et al. 2018). However, in regions with hydrophobic soils, such as those affected by intense fire activity or exceptional drought conditions, dry antecedent conditions combined with high intensity, short duration precipitation events (i.e., flash floods) can enhance flooding by increasing the ratio of surface runoff to infiltration (Barendrecht et al. 2024; Doerr et al. 2006).
TL;DR the soil beneath our feet is like the tines of a fountain pen