The Rainfall Intensity‐Duration Control of Debris Flows After Wildfire

Thomas, Matthew A.; Lindsay, Donald; Cavagnaro, David; Kean, Jason W.; McCoy, S. W.; Graber, Andrew

doi:10.1029/2023gl103645

Cited by 12 publications

(4 citation statements)

References 41 publications

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“…Rainfall intensity and duration is particularly important for sediment transport and prediction of debris flows (Cannon et al., 2010; Lane et al., 2006; Nyman et al., 2015; Thomas et al., 2023), which pose water‐quality and water‐supply concerns, and present a public safety hazard (Kean et al., 2019). Average storm intensity is often a significant predictor of the probability of debris flow, with short duration, low recurrence‐interval convective thunderstorms producing the greatest probability of debris flow, particularly in the intermountain Western U.S. (Cannon et al., 2010).…”

Section: Resultsmentioning

confidence: 99%

A Conceptual Framework to Assess Post‐Wildfire Water Quality: State of the Science and Knowledge Gaps

Elliott,

Hornberger,

Rosenberry

et al. 2024

Water Resources Research

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Wildfire substantially alters aquatic ecosystems by inducing moderate to catastrophic physical and chemical changes. However, the relations of environmental and watershed variables that drive those effects are complex. We present a Driver‐Factor‐Stressor‐Effect (DFSE) conceptual framework to assess the current state of the science related to post‐wildfire water‐quality. We reviewed 64 peer‐reviewed papers using the DFSE framework to identify drivers, factors, stressors, and effects associated with each study. A total of five drivers were identified and ranked according to their frequency of occurrence in the literature: atmospheric processes > fire characteristics > ecologic processes and characteristics > land surface characteristics > soil characteristics. Commonly reported stressors include increased nutrients, runoff, and sediment transport. Furthermore, although several different factors have been used at least once to explain water‐quality effects, relatively few factors outside of precipitation and fire characteristics are frequently studied. We identified several gaps indicating the need for long‐term monitoring, multi‐factor studies, consideration of organic contaminants, consideration of groundwater, and inclusion of soil characteristics. This assessment expands on other reviews and meta‐analyses by exploring causal linkages between influential variables and overall effects in post‐wildfire watersheds. Information gathered from our assessment and the framework itself can be used to inform future monitoring plans and as a guide for modeling efforts focused on better understanding specific processes or to mitigate potential risks of post‐wildfire water quality.

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Section: Resultsmentioning

confidence: 99%

A Conceptual Framework to Assess Post‐Wildfire Water Quality: State of the Science and Knowledge Gaps

Elliott,

Hornberger,

Rosenberry

et al. 2024

Water Resources Research

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“…Rainfall of intensity sufficient to initiate debris flows must also occur in the years following fire, and threshold rainfall intensities necessary for debris flows are expected to increase with time as the burned area recovers (Ebel, 2020; Hoch et al., 2021). In addition, spatially variable recovery rates within many burned areas (Kinoshita & Hogue, 2011) and increasing numbers of very large fires burning across hydroclimaticly diverse terrain (e.g., Thomas, Kean, et al., 2023; Thomas, Lindsay, et al., 2023) imply the need for refining the relationship between recovery and triggering intensity. Measuring recovery at smaller spatial scales (e.g., individual catchments) could help to address these issues.…”

Section: Discussionmentioning

confidence: 99%

“…We compiled 536 runoff‐generated debris‐flow records from 25 fires that offered variable timing of debris‐flow response following the fire (28–807 days after fire ignition) and a wide regional coverage across five western U.S. states (Figure 1a). This data set combined published debris‐flow inventories (DeGraff et al., 2022; McGuire, 2021; McGuire et al., 2021; Michel et al., 2019; Neptune et al., 2021; Rengers et al., 2021, 2023; Staley et al., 2016; Swanson et al., 2022; Tang et al., 2019; Thomas, Lindsay, et al., 2023) with new records we synthesized from field observations, photos, and reports collected by U.S. Geological Survey (USGS) staff and/or partner agencies (Graber, 2023) (Table S1 in Supporting Information ). Refer to Figure 1b for an example debris‐flow inventory from the 2012 Waldo Canyon Fire, Colorado.…”

Section: Methodsmentioning

confidence: 99%

How Long Do Runoff‐Generated Debris‐Flow Hazards Persist After Wildfire?

Graber,

Thomas,

Kean

2023

Geophysical Research Letters

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Runoff‐generated debris flows are a potentially destructive and deadly response to wildfire until sufficient vegetation and soil‐hydraulic recovery have reduced susceptibility to the hazard. Elevated debris‐flow susceptibility may persist for several years, but the controls on the timespan of the susceptible period are poorly understood. To evaluate the connection between vegetation recovery and debris‐flow occurrence, we calculated recovery for 25 fires in the western United States using satellite‐derived leaf area index (LAI) and compared recovery estimates to the timing of 536 debris flows from the same fires. We found that the majority (>98%) of flows occurred when LAI was less than 2/3 of typical prefire values. Our results show that total vegetation recovery is not necessary to inhibit runoff‐generated flows in a wide variety of regions in the western United States. Satellite‐derived vegetation data show promise for estimating the timespan of debris‐flow susceptibility.

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“…In particular, short-duration rainfall intensities (<15 min. ), which are a key predictor of runoff generation, have been shown to be the most likely to initiate debris flows (Kean et al, 2011;Thomas et al, 2023). The current USGS operational model (the M1 model described further in the methods section) predicts the probability of debris-flow initiation based on short-duration rainfall intensity, burn severity, slope steepness, and soil erodibility (Staley et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Evaluating Post-Wildfire Debris Flow Rainfall Thresholds and Volume Models at the 2020 Grizzly Creek Fire in Glenwood Canyon, Colorado, USA

Rengers,

Bower,

Knapp

et al. 2023

Preprint

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Abstract. As wildfire increases in the western United States, so do postfire debris-flow hazards. The U.S. Geological Survey (USGS) has developed two separate models to estimate (1) rainfall intensity thresholds for postfire debris flow initiation and (2) debris-flow volumes. However, the information necessary to test the accuracy of these models is seldom available. Here, we studied how well these models performed over a two-year period in the 2020 Grizzly Creek Fire burn perimeter in Glenwood Canyon, Colorado, USA, through the development of a debris flow response inventory. The study area had the advantage of a network of 11 rain gauges for rainfall intensity measurements and repeat lidar data for volume estimates. Our observations showed that 89 % of observed debris flows in the first year postfire were triggered by rainfall rates higher than the fire-wide rainfall threshold produced by the current USGS operational model (M1). No debris flows were observed in the second year postfire, despite eight rainstorms with intensities higher than the modeled rainfall threshold. We found that the operational model for debris flow initiation rainfall thresholds works well in this region during the first year but may be too conservative in year 2 due to vegetation recovery and sediment exhaustion. However, rainfall thresholds in the second year can be improved by using updated remote sensing imagery to recalculate the debris-flow initiation probability with the M1 model. The current volume model overpredicts for this region by a median value of 4.4 times. However, the offset between the predictions and observations is linear, and the volumes from the Grizzly Creek debris flows had a similar magnitude to historic postfire debris flows in the region. Consequently, the current volume model could be adjusted with a regional correction factor.

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The Rainfall Intensity‐Duration Control of Debris Flows After Wildfire

Cited by 12 publications

References 41 publications

A Conceptual Framework to Assess Post‐Wildfire Water Quality: State of the Science and Knowledge Gaps

A Conceptual Framework to Assess Post‐Wildfire Water Quality: State of the Science and Knowledge Gaps

How Long Do Runoff‐Generated Debris‐Flow Hazards Persist After Wildfire?

Evaluating Post-Wildfire Debris Flow Rainfall Thresholds and Volume Models at the 2020 Grizzly Creek Fire in Glenwood Canyon, Colorado, USA

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