Soil & Water Res., X:X | DOI: 10.17221/26/2026-SWR

Reduction in hydraulic conductivity for high burn severity soils begins after the first rainfall event: Results from laboratory-scale rainfall simulation experimentsOriginal Paper

Nana Afua Gyau Frimpong¹, Jacob Huerta², Ryan Webb ORCID...¹

¹ Department of Civil & Architectural Engineering and Construction Management, University of Wyoming, Laramie, Wyoming, USA

² Department of Mechanical Engineering, University of Wyoming, Laramie, Wyoming, USA

Wildfires can greatly impact the hydraulic properties of soil. This study aims to utilise laboratory experiments to simulate burned soil conditions under a range of slope angles and rainfall intensities to address the research question: How does the presence of ash after the first rainfall event impact the hydraulic properties of burned soil in complex terrain? Sandy loam soils for this study were sourced from a mixed conifer forested area in the San Juan Mountains of southern Colorado, USA. Measurements of soil hydraulic properties in experimental microplots were taken (1) before burning, (2) after burning, and (3) 24 hours after a rainfall simulation. A total of 15 experimental microplots with ash applied were run through rainfall simulations at slope angles ranging from 10° to 30°. Results found ash eroded had no significant relation to slope angle, but there was a significant reduction in field saturated hydraulic conductivity of samples with ash after rainfall simulations. To build on the findings presented here, future research should conduct field-based studies across various ecosystems and soil types to observe post-fire soil changes over time.

Keywords: post-wildfire hydrology; soil hydraulic conductivity; soil sealing; surface crust

Received: February 25, 2026; Accepted: April 16, 2026; Prepublished online: June 1, 2026