Supplementary material to "Brief Communication: Meteorological and climatological conditions associated with the 9 January 2018 post-fire debris flows in Montecito and Carpinteria California, USA"

ABSTRACT The post–Thomas Fire debris flows of 9 January 2018 killed 23 people, damaged 558 structures, and caused severe damage to infrastructure in Montecito and Carpinteria, CA. U.S. Highway 101 was closed for 13 days, significantly impacting transportation and commerce in the region. A narrow cold frontal rain band generated extreme rainfall rates within the western burn area, triggering runoff-driven debris flows that inundated 5.6 km2 of coastal land in eastern Santa Barbara County. Collectively, this series of debris flows is comparable in magnitude to the largest documented post-fire debris flows in the state and cost over a billion dollars in debris removal and damages to homes and infrastructure. This study summarizes observations and analyses on the extent and magnitude of inundation areas, debris-flow velocity and volume, and sources of debris-flow material on the south flank of the Santa Ynez Mountains. Additionally, we describe the atmospheric conditions that generated intense rainfall and use precipitation data to compare debris-flow source areas with spatially associated peak 15 minute rainfall amounts. We then couple the physical characterization of the event with a compilation of debris-flow damages to summarize economic impacts.

Download Full-text

Inundation, flow dynamics, and damage in the 9 January 2018 Montecito debris-flow event, California, USA: Opportunities and challenges for post-wildfire risk assessment

Geosphere ◽

10.1130/ges02048.1 ◽

2019 ◽

Vol 15 (4) ◽

pp. 1140-1163 ◽

Cited By ~ 23

Author(s):

J.W. Kean ◽

D.M. Staley ◽

J.T. Lancaster ◽

F.K. Rengers ◽

B.J. Swanson ◽

...

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Field Measurements ◽

Economic Loss ◽

Flow Dynamics ◽

Dynamic Constraints ◽

Fire Debris ◽

Velocity Information ◽

Intense Burst ◽

Comprehensive Framework

Abstract Shortly before the beginning of the 2017–2018 winter rainy season, one of the largest fires in California (USA) history (Thomas fire) substantially increased the susceptibility of steep slopes in Santa Barbara and Ventura Counties to debris flows. On 9 January 2018, before the fire was fully contained, an intense burst of rain fell on the portion of the burn area above Montecito, California. The rainfall and associated runoff triggered a series of debris flows that mobilized ∼680,000 m3 of sediment (including boulders >6 m in diameter) at velocities up to 4 m/s down coalescing urbanized alluvial fans. The resulting destruction (including 23 fatalities, at least 167 injuries, and 408 damaged homes) underscores the need for improved understanding of debris-flow runout in the built environment, and the need for a comprehensive framework to assess the potential loss from debris flows following wildfire. We present observations of the inundation, debris-flow dynamics, and damage from the event. The data include field measurements of flow depth and deposit characteristics made within the first 12 days after the event (before ephemeral features of the deposits were lost to recovery operations); an inventory of building damage; estimates of flow velocity; information on flow timing; soil-hydrologic properties; and post-event imagery and lidar. Together, these data provide rare spatial and dynamic constraints for testing debris-flow runout models, which are needed for advancing post-fire debris-flow hazard assessments. Our analysis also outlines a framework for translating the results of these models into estimates of economic loss based on an adaptation of the U.S. Federal Emergency Management Agency’s Hazus model for tsunamis.

Download Full-text

Objective definition of rainfall intensity–duration thresholds for the initiation of post-fire debris flows in southern California

Landslides ◽

10.1007/s10346-012-0341-9 ◽

2012 ◽

Vol 10 (5) ◽

pp. 547-562 ◽

Cited By ~ 132

Author(s):

Dennis M. Staley ◽

Jason W. Kean ◽

Susan H. Cannon ◽

Kevin M. Schmidt ◽

Jayme L. Laber

Keyword(s):

Debris Flows ◽

Southern California ◽

Rainfall Intensity ◽

Fire Debris ◽

Definition Of

Download Full-text

Is aridity a high-order control on the hydro–geomorphic response of burned landscapes?

International Journal of Wildland Fire ◽

10.1071/wf14079 ◽

2016 ◽

Vol 25 (3) ◽

pp. 262 ◽

Cited By ~ 15

Author(s):

Gary J. Sheridan ◽

Petter Nyman ◽

Christoph Langhans ◽

Jane Cawson ◽

Philip J. Noske ◽

...

Keyword(s):

Debris Flows ◽

Scale Parameter ◽

Landscape Scale ◽

High Order ◽

Net Radiation ◽

Erosion Rates ◽

Geomorphic Response ◽

Eastern Australia ◽

Fire Debris

Fire can result in hydro–geomorphic changes that are spatially variable and difficult to predict. In this research note we compile 294 infiltration measurements and 10 other soil, catchment runoff and erosion datasets from the eastern Victorian uplands in south-eastern Australia and argue that higher aridity (a function of the long-term mean precipitation and net radiation) is associated with lower post-fire infiltration capacities, increasing the chance of surface runoff and strongly increasing the chance of debris flows. Post-fire debris flows were only observed in the more arid locations within the Victorian uplands, and resulted in erosion rates more than two orders of magnitude greater than non-debris flow processes. We therefore argue that aridity is a high-order control on the magnitude of post-wildfire hydro–geomorphic processes. Aridity is a landscape-scale parameter that is mappable at a high resolution and therefore is a useful predictor of the spatial variability of the magnitude of post-fire hydro–geomorphic responses.

Download Full-text

Minimizing economic impacts from post-fire debris flows in the western United States

Natural Hazards ◽

10.1007/s11069-016-2306-0 ◽

2016 ◽

Vol 83 (1) ◽

pp. 149-176 ◽

Cited By ~ 6

Author(s):

Kevin McCoy ◽

Vitaliy Krasko ◽

Paul Santi ◽

Daniel Kaffine ◽

Steffen Rebennack

Keyword(s):

United States ◽

Debris Flows ◽

Economic Impacts ◽

Western United States ◽

Fire Debris

Download Full-text

Brief communication: Meteorological and climatological conditions associated with the 9 January 2018 post-fire debris flows in Montecito and Carpinteria, California, USA

Natural Hazards and Earth System Science ◽

10.5194/nhess-18-3037-2018 ◽

2018 ◽

Vol 18 (11) ◽

pp. 3037-3043 ◽

Cited By ~ 19

Author(s):

Nina S. Oakley ◽

Forest Cannon ◽

Robert Munroe ◽

Jeremy T. Lancaster ◽

David Gomberg ◽

...

Keyword(s):

High Intensity ◽

Debris Flows ◽

Southern California ◽

Cold Front ◽

Santa Barbara ◽

Fire Debris ◽

Orographic Enhancement

Abstract. The Thomas Fire burned 114 078 ha in Santa Barbara and Ventura counties, southern California, during December 2017–January 2018. On 9 January 2018, high-intensity rainfall occurred over the Thomas Fire burn area in the mountains above the communities of Montecito and Carpinteria, initiating multiple devastating debris flows. The highest rainfall intensities occurred with the passage of a narrow rainband along a cold front oriented north to south. Orographic enhancement associated with moist southerly flow immediately ahead of the cold front also played a role. We provide an explanation of the meteorological characteristics of the event and place it in historic context.

Download Full-text

Towards real-time global assessment of post-fire debris flow hazards with remotely sensed data

10.5194/egusphere-egu21-13846 ◽

2021 ◽

Author(s):

Elijah Orland ◽

Dalia Kirschbaum ◽

Thomas Stanley

Keyword(s):

Remote Sensing ◽

Debris Flow ◽

Real Time ◽

Debris Flows ◽

Remotely Sensed Data ◽

Model Framework ◽

Burned Areas ◽

Early Results ◽

Fire Debris ◽

Debris Flow Initiation

<p>As the risk of wildfires increases worldwide, burned steeplands are vulnerable to the secondary hazard of widespread sediment mobilization through debris flows. Following an initial burn, sediment and soil previously restrained by vegetation are no longer consolidated, allowing for easy mobilization into channels and along steep hillslopes through runoff. &#160;Sufficiently powerful rainfall incorporates entrained material into turbulent flows and serves as the primary trigger for debris flow initiation. There is thus an ongoing need to establish the relationship between rainfall and debris flow initiation based on a variety of spatiotemporal preconditions. Previous work establishes regional and local thresholds to constrain the effect of rainfall in recently burned areas, but no empirical or numerical solution has worldwide application. Building from regionally-based efforts in the U.S., this work considers how remote sensing data can be applied to better approximate the post-fire debris flow hazards worldwide using freely available global datasets and software. Our work assesses the utility of remote sensing resources for analyzing burn characteristics, topography, rainfall intensity/duration, and, thus, debris flow initiation. Early results show that global observations are sufficient to delineate background rainfall rates from storms likely to cause debris flows across a variety of burn severity and topographic conditions. However, the dearth of publicly-available post-fire debris flow inventories globally limit the ability to test how the model framework performs within different climatologic and morphologic areas. This work will present preliminary analysis over the Western United States and demonstrate the feasibility of a global, near-real time model to provide situational awareness of potential hazards within recently burned areas worldwide. Future work will also consider how global or regional precipitation forecasts may increase the lead time for improved early warning of these hazards.</p>

Download Full-text

Time Since Burning and Rainfall Characteristics Impact Post-Fire Debris-Flow Initiation and Magnitude

Environmental and Engineering Geoscience ◽

10.2113/eeg-d-20-00029 ◽

2021 ◽

Vol 27 (1) ◽

pp. 43-56

Author(s):

Luke A. McGuire ◽

Francis K. Rengers ◽

Nina Oakley ◽

Jason W. Kean ◽

Dennis M. Staley ◽

...

Keyword(s):

Numerical Modeling ◽

Debris Flow ◽

Debris Flows ◽

Numerical Models ◽

Ground Cover ◽

Temporal Changes ◽

Infiltration Capacity ◽

Rainfall Characteristics ◽

San Gabriel Mountains ◽

Fire Debris

ABSTRACT The extreme heat from wildfire alters soil properties and incinerates vegetation, leading to changes in infiltration capacity, ground cover, soil erodibility, and rainfall interception. These changes promote elevated rates of runoff and sediment transport that increase the likelihood of runoff-generated debris flows. Debris flows are most common in the year immediately following wildfire, but temporal changes in the likelihood and magnitude of debris flows following wildfire are not well constrained. In this study, we combine measurements of soil-hydraulic properties with vegetation survey data and numerical modeling to understand how debris-flow threats are likely to change in steep, burned watersheds during the first 3 years of recovery. We focus on documenting recovery following the 2016 Fish Fire in the San Gabriel Mountains, California, and demonstrate how a numerical model can be used to predict temporal changes in debris-flow properties and initiation thresholds. Numerical modeling suggests that the 15-minute intensity-duration (ID) threshold for debris flows in post-fire year 1 can vary from 15 to 30 mm/hr, depending on how rainfall is temporally distributed within a storm. Simulations further demonstrate that expected debris-flow volumes would be reduced by more than a factor of three following 1 year of recovery and that the 15-minute rainfall ID threshold would increase from 15 to 30 mm/hr to greater than 60 mm/hr by post-fire year 3. These results provide constraints on debris-flow thresholds within the San Gabriel Mountains and highlight the importance of considering local rainfall characteristics when using numerical models to assess debris-flow and flood potential.

Download Full-text