Hyper-dry conditions provide new insights into the cause of extreme floods after wildfire

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A catastrophic wildfire in the foothills of the Rocky Mountains near Boulder, Colorado provided a unique opportunity to investigate soil conditions immediately after a wildfire and before alteration by rainfall. Measurements of near-surface (< 6 cm) soil properties (temperature, volumetric soil-water content, θ; and matric suction, ψ), rainfall, and wind velocity were started 8 days after the wildfire began. These measurements established that hyper-dryconditions (θ < ~ 0.02 cm3 cm-3; ψ > ~ 3 x 105 cm) existed and provided an in-situ retention curve for these conditions. These conditions exacerbate the effects of water repellency (natural and fire-induced) and limit the effectiveness of capillarity and gravity driven infiltration into fire-affected soils. The important consequence is that given hyper-dryconditions, the critical rewetting process before the first rain is restricted to the diffusion–adsorption of water-vapor. This process typically has a time scale of days to weeks (especially when the hydrologic effects of the ash layer are included) that is longer than the typical time scale (minutes to hours) of some rainstorms, such that under hyper-dryconditions essentially no rain infiltrates. The existence of hyper-dryconditions provides insight into why, frequently during the first rain storm after a wildfire, nearly all rainfall becomes runoff causing extremefloods and debris flows.
Publication type Article
Publication Subtype Journal Article
Title Hyper-dry conditions provide new insights into the cause of extreme floods after wildfire
Series title Catena
DOI 10.1016/j.catena.2012.01.006
Volume 93
Year Published 2012
Language English
Publisher Elsevier
Publisher location Amsterdam, Netherlands
Contributing office(s) Branch of Regional Research-Central Region
Description 6 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Catena
First page 58
Last page 63
Country United States
State Colorado
City Boulder
Other Geospatial Rocky Mountains
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