A Shorter, Sharper Rainy Season Amplifies California Wildfire Risk

Swain, Daniel L.

doi:10.1029/2021gl092843

Cited by 72 publications

(62 citation statements)

References 34 publications

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“…Observations over the past 60 years demonstrate a delayed onset of the rainy season in California (Lukovic et al., 2021). This allows dry conditions to extend into the autumn/winter offshore wind season (Abatzoglou et al., 2021; Swain, 2021), amplifying wildfire risk (Goss et al., 2020). Climate model projections suggest further “sharpening” of the precipitation season (Swain et al., 2018), exacerbating the potential for increased wildfire activity and shortening the timespan between major wildfires and the onset of precipitation.…”

Section: Debris Flow Recurrence Interval As a Pre‐fire Decision Support Toolmentioning

confidence: 99%

A Warming Climate Adds Complexity to Post‐Fire Hydrologic Hazard Planning

Oakley

2021

Earth's Future

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Wildfire removes vegetation and weakens root strength, making burned areas more susceptible to erosion. Wildfire can also alter the physical and chemical characteristics of soil, creating a hydrophobic layer which increases runoff and may lead to damaging floods and debris flows in steep terrain. For example, following the 2017 Thomas Fire in Southern California, the devastating 9 January 2018 debris flows in the community of Montecito resulted in 23 deaths and nearly $1B in damages (Lancaster et al., 2021). In a meeting following the event, a Santa Barbara County resource manager made a plea to researchers: "I need to know how frequently I can expect post-fire debris flows of this magnitude in this area." Managers in other susceptible areas have expressed similar concerns for events in their area of responsibility.Impactful post-fire debris flows are not new to southern California, though the penultimate fatality event occurred in 2003 when 16 people died in debris flows emanating from the Old/Grand Prix burn areas in the San Bernardino Mountains (Oakley et al., 2017). The Montecito event renewed focus on post-fire debris-flow preparedness, with understanding the recurrence intervals of these events in the current and future climate as key concerns in planning efforts. Southern California's well-documented history of impactful post-fire debris flows compared to other susceptible regions makes it an excellent "laboratory" for research and development of decision support tools. Kean and Staley (2021) utilize Southern California's data to provide the first known framework to estimate recurrence intervals for minor and major post-fire debris flows in the region. This tool allows for evaluation of recurrence intervals in both a stationary and warming climate. Emerging research from disciplines relevant to post-fire hazards (e.g., soil, wildfire, and climate science) can be readily integrated into this framework. While regionally focused, this tool is applicable to other locations susceptible to post-wildfire debris flows provided the requisite data on rainfall triggering thresholds, burn severity, and wildfire recurrence can be collected. Debris Flow Recurrence Interval as a Pre-Fire Decision Support ToolThe time between wildfire and precipitation events is decidedly brief in California, such that pre-fire planning presents significant advantages. For example, the 2018 Montecito debris flow occurred before the Thomas Fire was 100% contained (Lancaster et al., 2021). Observations over the past 60 years demonstrate a delayed onset of the rainy season in California (Lukovic et al., 2021). This allows dry conditions to extend into the autumn/winter offshore wind season (Abatzoglou et al., 2021;Swain, 2021), amplifying wildfire risk (Goss et al., 2020). Climate model projections suggest further "sharpening" of the precipitation Abstract Climate change will likely increase the frequency of damaging post-wildfire floods and debris flows, amplifying the threat to life, property, and infrastructure situated in susceptible are...

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Section: Debris Flow Recurrence Interval As a Pre‐fire Decision Support Toolmentioning

confidence: 99%

A Warming Climate Adds Complexity to Post‐Fire Hydrologic Hazard Planning

Oakley

2021

Earth's Future

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“…Conceptually, the temperature regressor provides a measure of longer term drought stress than the short term monthly timeseries. The precipitation regressor captures the sharpness of precipitation regimes, which has been shown to amplify wildfire risk in California (56). In practice, including these extra regressors improved overall model performance only slightly, but allowed the model to better reproduce both monthly trends, interannual variability, and the observed increase in burn area over the observation period, a large fraction of which has been attributed to climate change (see Figures S7-8).…”

Section: Firementioning

confidence: 99%

Climate risks to carbon sequestration in US forests

Anderegg

Chegwidden

Badgley

et al. 2021

Preprint

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Forests are currently a substantial carbon sink globally. Many climate change mitigation strategies rely on forest preservation and expansion, but the effectiveness of these approaches hinges on forests sequestering carbon for centuries despite anthropogenic climate change. Yet climate-driven disturbances pose critical risks to the long-term stability of forest carbon. We quantify the key climate drivers that fuel wildfire, drought, and insects, for the United States over 1984-2018 and project future disturbance risks over the 21st century. We find that current risks are widespread and projected to increase across different emission scenarios by a factor of 4-14 for fire and 1.3-1.8 for drought and insects. Our results provide insights for carbon cycle modeling, conservation, and climate policy, underscoring the escalating climate risks facing forests and the need for emissions reductions to mitigate climate change.

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“…During the 1970s, 1980s, and 1990s, only 4 large fire cases occurred while there was no large fire case from the 1940s to 1960s. This increasing trend of large wildfire numbers may be associated with longterm fuel conditions, human activity, and climate warming (Goss et al, 2020;Mass and Ovens, 2019;Swain, 2021;Williams et al, 2019). Among these 20 large cases, 7 were caused by lightning, 6 were linked to human related activity, 2 were associated with power lines, 3 were under investigation and 1 was undetermined.…”

Section: Three Large Wildfires In 2018mentioning

confidence: 99%

“…The relationship between long-term increased fires and the warmdry trend is widely mentioned (Goss et al, 2020;Swain, 2021). Williams et al (2019) found that California wildfires experienced a fivefold increase in the annual burned area, mainly due to more than an eightfold increase in summer forest fire extent from 1972 to 2018.…”

Section: Introductionmentioning

confidence: 99%

Opposite anomalous synoptic patterns for potential California large wildfire spread and extinguishing in 2018 cases

Qian

et al. 2021

Atmospheric Research

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The consecutive occurrence of three large wildfires in 1 year is rarely seen in northern California including the deadliest case during 8-25 November 2018 in Butte County. They happened under favorable fuel and meteorological conditions including long-term warming trends, normal summer-autumn warm-dry climate, and extreme heated air masses with strong offshore wind. The former two meteorological conditions contribute a background for large wildfires but extreme heated air masses and strong offshore winds are critical potentials for a fire spread. The relationship between extreme heated/cooled air masses and the three large wildfires was carefully examined from their starts to extinguishing. An anomaly-based synoptic analysis method is used by separating atmospheric variables into climatology and anomalies. A 3-dimensional anomalous synoptic pattern of atmospheric variables is established for the three wildfire cases in 2018. The analysis showed that one anomalous warm-air mass in the mid-to-low troposphere dynamically associated with a positive center of geopotential height (GPH) anomalies at the upper troposphere (150-300 hPa) is an anomalous synoptic pattern indicating a potential large wildfire spread, and conversely by negative anomalies when the fires were extinguished. The ECMWF model seems to be capable of predicting such anomalous temperature-pressure patterns to indicate possible fire spread and extinguishing.

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A Shorter, Sharper Rainy Season Amplifies California Wildfire Risk

Cited by 72 publications

References 34 publications

A Warming Climate Adds Complexity to Post‐Fire Hydrologic Hazard Planning

A Warming Climate Adds Complexity to Post‐Fire Hydrologic Hazard Planning

Climate risks to carbon sequestration in US forests

Opposite anomalous synoptic patterns for potential California large wildfire spread and extinguishing in 2018 cases

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