Rainfall-intensity thresholds for post-wildfire debris-flow initiation vary with climatology of peak rainfall intensity

Rainfall-intensity thresholds for post-wildfire debris-flow initiation are the primary criteria for issuing debris-flow hazard warnings in burned landscapes. Yet, with the expansion of frequent wildfires into a wide range of hydroclimates, there is a growing need for accurate thresholds in landscapes with few to no observations of post-fire debris-flow activity on which to constrain them (such as in Northern California and the Pacific Northwest). To help constrain thresholds in these burned landscapes, I will present fire-scale observations of rainfall intensities associated with post-wildfire debris-flow initiation across the western US that indicate rainfall-intensity thresholds for post-fire debris-flow initiation are systematically higher at sites that frequently experience higher maximum rainfall intensities. In particular, there is a strong correlation between the 15-minute rainfall-intensity threshold and the peak 15-minute rainfall intensity of storms with a one-year return interval. In the second part of the talk, I will explore a growing dataset of soil properties measured in burned landscapes across a range of hydroclimates and propose some physical mechanisms that help explain such a correlation.

Speaker: Scott McCoy, University of Nevada, Reno