Landsliding follows signatures of wildfire history and vegetative regrowth in a steep coastal shrubland

Geosphere
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Abstract

Five years after the deadly and destructive 9 January 2018 Montecito debris flows (Santa Barbara County, California, USA), an atmospheric river storm on 9 January 2023 triggered widespread landsliding that affected many of the same drainages in the Santa Ynez Mountains. Using high-resolution aerial imagery, we identified >10,000 landslides over an ∼160 km2 area. Most of the landslides were shallow (<1 m in depth) translational debris slides that initiated on steep (∼40°), south-facing hillslopes, with the highest incidence of landsliding in a sandstone-dominated bedrock unit. The landslides mobilized into debris flows and delivered substantial quantities of sediment downstream, which contributed to costly infrastructure impairments. We detected order-of-magnitude differences in landslide density across the study area that could not be attributed to variations in geomorphology (topographic aspect and slope), geology (bedrock type), or hydrology (seasonal antecedent rainfall, peak hourly storm rainfall intensity, total storm rainfall), which are usually considered relevant factors for shallow landsliding. Rather, we found that vegetation regrowth following wildfire was likely a relevant factor associated with the highly variable landslide densities. Hillslopes with less and different types of vegetation regrowth after fire appear to have been more susceptible to shallow landslides. We identify a possible vegetation control on postfire landsliding, which highlights an opportunity for hypothesis testing using more advanced techniques to track the evolution of vegetation cover and vegetation type in steep shrubland environments following wildfire.

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Publication type Article
Publication Subtype Journal Article
Title Landsliding follows signatures of wildfire history and vegetative regrowth in a steep coastal shrubland
Series title Geosphere
DOI 10.1130/GES02856.1
Volume 21
Issue 5
Publication Date August 11, 2025
Year Published 2025
Language English
Publisher Geological Society of America
Contributing office(s) Geologic Hazards Science Center - Landslides / Earthquake Geology
Description 18 p.
First page 823
Last page 840
Country United States
State California
County Santa Barbara County
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