The Enormous Flaw in Wildfire Data

by Sarah Hyden

 August 2, 2024
Facebook

TwitterRedditEmail

Tanques Fire, i.e. Tanques Intentional Burn   Photo: U.S. Forest Service.

Both Congress and the U.S. Forest Service have told us that our forests and communities are experiencing a “wildfire crisis” – that an increasing amount of wildfire is burning on our landscapes, and fire severity is increasing. The primary “solution” they are currently planning and implementing, embodied in the Wildfire Crisis Strategy, is a substantial increase in logging, thinning and burning treatments in our forests, for which Congress has provided billions of dollars of funding, along with the mandate to get it done.

So that begs the question – to what extent are we actually in a wildfire crisis? Certainly the aggressive and environmentally damaging logging and over-burning that is being carried out in some forests, with much more to come, should be based on solid data and science.

The basic premise of the Wildfire Crisis Strategy is that wildfire is greatly increasing on our western landscapes. One would think that this should not be difficult to ascertain, as the Forest Service and other land management agencies maintain records and maps of wildfire perimeters. This data goes into national wildfire databases, such as MTBS (Monitoring Trends in Burn Severity). MTBS is “an interagency program to map the location, extent and associated burn severity of all large fires (including wildfire, wildland fire use and prescribed fire) in the United States across all ownerships from 1984 to present,” This program is largely run by the USGS and the US Forest Service, and datasets include state and federal fire history records.

However, Forest Service wildfire perimeter data is vastly compromised in that a large proportion of acres burned within the officially designated wildfire perimeters are actually ignited by the US Forest Service themselves, most often by aerial ignitions via drones and helicopters. In many cases, the majority of a fire that is called a “wildfire” on national forest lands is actually Forest Service intentional burning. This strategy for managing fire has increased to the point that numerous fires are substantially expanded by intentional burning.

Currently, the Tanques Fire in the Santa Fe National Forest, originally ignited by a lightning strike, is being expanded through aerial and ground firing operations under command of the Forest Service. According to a Forest Service news release, the fire was first reported on July 18, and by July 25, the fire had grown to only 13 acres.

Around that point the Forest Service made the decision to expand the fire up to 7,000 acres with firing operations, utilizing both aerial and hand ignitions. That means the Forest Service intended to expand it up to 538X its size. The fire may have continued to slowly expand naturally, but relatively high vegetation moisture from recent rains made it unlikely that the fire would spread much on its own. It’s hard to say exactly which part of the potential 7,000 acre “wildfire” will be due to intentional burning, and which will be “natural” wildfire, but it is clear the vast majority of the acres burned will be due to USFS ignitions. Nonetheless, the Forest Service is calling the Tanques Fire a wildfire.

Recently, the Forest Service and The Nature Conservancy (an organization closely aligned with the Forest Service), along with a university professor, authored the “Tamm review: A meta-analysis of thinning, prescribed fire, and wildfire effects on subsequent wildfire severity in conifer dominated forests of the Western US.” This review is a consideration of the efficacy of forest “thinning” and prescribed fire in moderating the incidence and severity of wildfire. It begins with citing a research article to support their contention that “In the western United States, area burned [by wildfire] has doubled in recent decades (Iglesias et al., 2022).”

Map of Tanques Fire 7,000 Acre Focal Area and Planning Area    U.S. Forest Service.

This research article, “U.S. fires became larger, more frequent, and more widespread in the 2000s,” is based on data from over 28,000 fires in the MTBS dataset. Since this dataset is derived largely from Forest Service wildfire data, it includes the large proportion of fire intentionally set by the Forest Service during wildfire management operations. The agency does not differentiate in their published wildfire data between fire ignited during wildfire management operations and fire that burned due to the original wildfire ignition. The study concludes that there have been more fires and larger fires in the west since 1999 – yet we have no way of knowing to what extent this is true, given that the Forest Service is igniting more and more fire under the umbrella of wildfire management, and calling it all wildfire.

The first publicized example of such wildfire expansion was the 2002 Biscuit Fire. Timothy Ingalsbee, PhD of Firefighters United for Safety, Ethics, and Ecology estimated that a large proportion of the Biscuit Fire was ignited by Forest Service firing operations. Inglasbee stated in a 2006 report largely focused on the Biscuit Fire: “…burnout operations can sometimes take place several miles away from the edge of a wildfire, or alternately, miles away from the fire containment line.” Wildfire expansions have increased since 2002, and wildfire starts, such as lightning strike ignitions, are often simply the “match that lit the fire” leading to numerous firing operation ignitions to implement intentional burns that they call wildfires.

The Tamm Review “found overwhelming evidence that mechanical thinning with prescribed burning, mechanical thinning with pile burning, and prescribed burning only, are effective at reducing subsequent wildfire severity.” Those conclusions are controversial and do not consider research from independent scientists. But a more fundamental issue with the Review is that the purpose and need for such aggressive forest treatments are at least partially predicated on flawed data that indicates wildfire has doubled on our landscapes in recent decades. It may be increasing given the warming and drying climate and the abundance of fuels, but who knows to what extent, since the wildfire data is so skewed by the inclusion of the Forest Service intentional burns. This data issue also affects considerations of trends in fire severity, and this should be investigated.

A significant proportion of wildfire research depends on wildfire perimeter data, including the Iglesias et al. research referenced as support for the premise of the Tamm Review. It is clear we have little knowledge of how much fire that was not ignited by the Forest Service has burned on our landscape in recent decades. It’s a major flaw in “wildfire” data. No forest management actions should be contemplated or initiated based on such data.

That Congress and the Forest Service are going forward with a strategy for addressing the “WIldfire Crisis,” without having determined with reasonable data and responsible science to what extent the crisis exists, is unacceptable  – especially considering that the remedy often involves severely damaging impacts to our forests and communities. There needs to be clear parameters developed for how to support appropriate amounts of fire on our landscapes, and any resulting plan should be analyzed with an environmental impact statement.

There is understandable concern about wildfires increasingly impacting wildland/urban interface communities, and this issue requires serious consideration and action. However, evidence clearly shows that burning of homes and communities by wildfire is not significantly impacted by logging, thinning and intentional burning treatments out in the forest, that only the 100 feet surrounding homes and other structures is relevant to structure ignitions. The best response to the home ignition problem is home hardening and treating the landscape immediately surrounding homes and other values. This takes a coordinated effort between governmental bodies, land management agencies and the public. Such coordination would more likely occur with increased transparency on the part of the Forest Service and affiliated scientists, which could build trust with the public. The accurate collection and categorization of wildfire data, which underlies research concerning wildfire, is a fundamental basis for transparency and trust – and good science.

Sarah Hyden has been working to protect the Santa Fe National Forest for well over a decade. She was a co-founder of the Santa Fe Forest Coalition and was the WildEarth Guardians’ Santa Fe National Forest Advocate. In 2019, she co-founded The Forest Advocate, a not-for-profit organization dedicated to protection of the Santa Fe National Forest and all western forests. The Forest Advocate maintains an active website that publishes forest advocacy news and resources — theforestadvocate.org.

Wildfire resilience requires action from all, explains IBHS Chief

Roy Wright presents latest scientific guidance during California Department of Insurance Workshop


NEWS PROVIDED BY Insurance Institute for Business & Home Safety (IBHS)

Dec 10, 2020


RICHBURG, S.C., Dec. 10, 2020 /PRNewswire/ -- As California grapples with the wildfire risk across the state, the Insurance Institute for Business & Home Safety (IBHS) today shared the latest science-based guidance to reduce wildfire risk during a California Department of Insurance workshop. Roy Wright, president & CEO of IBHS, brought the organization's scientific expertise from a decade of work at the IBHS Research Center and numerous post-fire field investigations to "Modeling Wildfire Risk and Mitigation in the Era of Climate Change."

"Wildfire risk to communities can be reduced, but it cannot be eliminated. Research in the field and in our lab has demonstrated the clear set of actions that must be taken to give homes a better chance. Yet, this set of actions requires stakeholders to work together to implement and vigilantly maintain wildfire-resistant properties," explains Wright. "Each home is a system with multiple vulnerabilities, so no single action alone will significantly reduce wildfire risk but, collaboratively, communities can bring down their risk."

IBHS lays out the actions for homeowners, neighborhoods and communities in its Suburban Wildfire Adaptation Roadmaps and Wildfire Ready guide for homeowners to walk stakeholders through the opportunities to reduce wildfire risk. Filling the need for actionable guidance specifically for closely-built suburban communities, the Suburban Wildfire Adaptation Roadmaps qualitatively describe the relative vulnerabilities of eight components of the home and actions to improve the risk. Wildfire Ready turns the nuanced technical report into a progressive guide for homeowners that prioritizes the actions that give a home a better chance of surviving a wildfire.

"Embers can pick up and loft regularly more than half a mile. This ability to transport themselves fundamentally changes who is at risk to wildfire because once fire enters a community a domino effect begins as one burning home generates more lofted embers and produces radiant heat making the neighboring homes vulnerable. This domino effect makes community adaptation vital to wildfire mitigation," continues Wright, a northern California native who grew up with wildfire risk. "Communities, neighborhoods, and individuals must work together using wildfire resistant materials and designs as well as vigilant maintenance."

IBHS is committed to producing leading wildfire research that delivers actionable guidance to empower home- and businessowners to prevent avoidable loss.

"As we dive even deeper into wildfire science, we must apply the learnings we already have to improve communities' chances against wildfire. The roof, the 0-5-foot home ignition zone, the area underneath a deck, and vents are the first items that must be addressed," Wright adds.

Home and business owners eager to take action against wildfire can explore Wildfire Ready and Wildfire Ready‒Business at disastersafety.org/wildfire.

About the Insurance Institute for Business & Home Safety (IBHS)
The IBHS mission is to conduct objective, scientific research to identify and promote effective actions that strengthen homes, businesses and communities against natural disasters and other causes of loss. Learn more about IBHS at DisasterSafety.org.

SOURCE Insurance Institute for Business & Home Safety (IBHS)
Related Links

www.disastersafety.org

EXCERPT

Observed Impacts of Anthropogenic Climate Change on Wildfire in California

A. Park Williams 

 

John T. Abatzoglou 

 

Alexander Gershunov 

 

Janin Guzman‐Morales 

 

Daniel A. Bishop 

 

Jennifer K. Balch 

 

Dennis P. Lettenmaier

First published: 15 July 2019

 

https://doi.org/10.1029/2019EF001210

Abstract

Recent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972–2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by warming. Since the early 1970s, warm‐season days warmed by approximately 1.4 °C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest‐fire area to VPD is exponential, meaning that warming has grown increasingly impactful. Robust interannual relationships between VPD and summer forest‐fire area strongly suggest that nearly all of the increase in summer forest‐fire area during 1972–2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California's diverse fire regimes, warming‐driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date.

Plain Language Summary

Since the early 1970s, California's annual wildfire extent increased fivefold, punctuated by extremely large and destructive wildfires in 2017 and 2018. This trend was mainly due to an eightfold increase in summertime forest‐fire area and was very likely driven by drying of fuels promoted by human‐induced warming. Warming effects were also apparent in the fall by enhancing the odds that fuels are dry when strong fall wind events occur. The ability of dry fuels to promote large fires is nonlinear, which has allowed warming to become increasingly impactful. Human‐caused warming has already significantly enhanced wildfire activity in California, particularly in the forests of the Sierra Nevada and North Coast, and will likely continue to do so in the coming decades.

1 Introduction

In the western United States, annual area burned increased substantially in recent decades due to increased frequency and size of large wildfires (Abatzoglou & Williams, 2016; Balch et al., 2018; Dennison et al., 2014; Westerling, 2016). It is well established that this observed increase in wildfire activity was promoted in many areas by reduced fuel moisture due to warming‐induced increases in evaporative demand, reduced snowpack, and reduced warm‐season precipitation frequency (Abatzoglou & Williams, 2016; Holden et al., 2018; Kitzberger et al., 2017; Westerling, 2016). These recent climate trends are broadly consistent with those expected from anthropogenic climate change (Abatzoglou & Williams, 2016), but anthropogenic climate effects on wildfire can vary greatly across space and time due to confounding factors such as natural climate variations, land and fire management practices, ignitions from humans, spatial diversity in vegetation type, and the complex ways in which these processes interact (Williams & Abatzoglou, 2016). Therefore, location‐specific adaptation responses to wildfire require understanding how climate affects wildfire locally, how the key climate variables have changed over the past several decades, and whether these climate changes are likely to continue.

Perhaps nowhere on Earth has received more attention regarding recent wildfire trends and their causes than California. One reason for the attention is that increases in statewide burned area over the last several decades were dramatically punctuated in 2017 and 2018 by particularly extreme wildfire activity with substantial loss of life and property. In 2017, modern state records were set for the largest individual wildfire (Thomas Fire: 114,078 ha) and the most structures destroyed by an individual wildfire (Tubbs Fire: 5,636 structures), which led to 22 fatalities (CalFire, 2018). The total area burned in 2017 was also nearly a state record at the time (505,293 ha), behind 2007. In 2018, state records were set for total area burned (676,312 ha), largest individual wildfire (Mendocino Complex Fire: 185,800 ha), and most destructive wildfire (Camp Fire: 18,804 structures destroyed, 85 fatalities). In these 2 years, California spent over $1.5 billion on fire suppression, far more than any previous 2‐year period (CalFire, 2018).

California is a particularly difficult place to disentangle the drivers of changing wildfire activity. California's climate, vegetation cover, and human settlement patterns are highly diverse, causing the influences of these factors on fire activity to be spatially heterogeneous and complex (Jin et al., 2014; Jin et al., 2015; Keeley & Syphard, 2017; Swetnam & Baisan, 2003; Westerling & Bryant, 2008). Humans dominate the wildfire regime across much of the state by altering land cover (Sleeter et al., 2011; Syphard et al., 2018), supplying the vast majority of ignitions (Balch et al., 2017; Nagy et al., 2018), and attempting to suppress essentially all fires. Fire suppression over the past century allowed for artificial buildup of fuels in many regions that historically experienced frequent low‐intensity fires, reducing fuel limitation as a constraint on fire activity and putting many areas into a so‐called fire deficit (Higuera et al., 2015; Marlon et al., 2012; Minnich et al., 1995; Parks et al., 2015). Even under constant climate conditions, changes in California's fire activity over the past century would be expected as populations increased and cities expanded into surrounding wildlands (Radeloff et al., 2018), fire suppression strategies evolved (Stephens & Ruth, 2005), and frequency and type of human‐ignited wildfires changed (Balch et al., 2017; Keeley & Syphard, 2018). Changes in these nonclimatic factors may also promote nonstationarity in fire‐climate relationships, confounding efforts to isolate the influence of climate change on fire activity (Higuera et al., 2015; Hurteau et al., 2019; Littell, 2018; Mann et al., 2016; Marlon et al., 2012; Taylor et al., 2016).

The effect of climate on wildfire in California is highly seasonal and variable across vegetation gradients. In summer, when fires are most frequent in California, large burned areas are promoted by the cumulative drying effects of atmospheric aridity and precipitation deficits mainly in forest ecosystems where fuel availability is not a limiting factor (Abatzoglou & Kolden, 2013; Jin et al., 2014; Keeley & Syphard, 2016; Swetnam, 1993; Swetnam & Betancourt, 1998; Westerling et al., 2003; Williams et al., 2018). In fall, many of California's most destructive fires occur in coastal shrublands and are driven by often extreme offshore downslope wind events, where synoptic conditions advect dry air masses often originating from the continental interior high desert westward and southward across topographic barriers such as the Transverse, Peninsular, and Coastal Ranges (Conil & Hall, 2006; Guzman‐Morales et al., 2016; Hughes & Hall, 2010; Moritz et al., 2010; Nauslar et al., 2018). The most widely studied offshore wind events, termed Santa Ana winds in southern California, increase in frequency in the fall and peak in winter (Abatzoglou et al., 2013; Raphael, 2003). Strong offshore winds with very low relative humidity can quickly dry fuels and spread large wildfires when they occur prior to the onset of the winter precipitation season in California's Mediterranean climate (Billmire et al., 2014; Keeley, 2004; Moritz et al., 2010; Westerling et al., 2004).

The effects of anthropogenic climate change on California's fire regimes are likely to be diverse and complex, varying by region and season (Liang et al., 2017; Pierce et al., 2018; Syphard et al., 2019; Westerling, 2018). Climate model projections of warming and increased atmospheric aridity in California are strong and robust across models (Pierce et al., 2013). It is well established that warming promotes wildfire throughout the western United States, particularly in forested regions, by enhancing atmospheric moisture demand and reducing summer soil moisture as snowpack declines (Abatzoglou & Williams, 2016; Westerling et al., 2006). By contrast, model projections of precipitation in California are highly uncertain but with a tendency toward increased precipitation annual totals, particularly in northern California during winter (Maloney et al., 2013). However, many climate models have systematic biases in North Pacific storm tracks and tropical Pacific sea surface temperatures that should lead to strong skepticism regarding model simulations of future precipitation in California (Seager et al., 2019; Simpson et al., 2016). Climate models also project precipitation frequency declines in spring through fall that would partly offset winter increases, resulting in increased precipitation variability (AghaKouchak et al., 2018; Pierce et al., 2018; Polade et al., 2014; Polade et al., 2017; Swain et al., 2018). In fall, models project reduced frequency and intensity of Santa Ana wind events (Guzman‐Morales & Gershunov, 2019; Hughes et al., 2011). However, concurrent warming and decreased fall precipitation may, to some degree, counteract the effects of reduced offshore winds on fall fire risk in southwestern California (Hughes et al., 2011; Pierce et al., 2018), possibly extending the fire season towards the winter peak of the downslope wind season (Guzman‐Morales & Gershunov, 2019; Syphard et al., 2018).

While much has been published on projected changes in wildfire activity due to climate change (e.g., Barbero et al., 2015; Hurteau et al., 2019; Krawchuk & Moritz, 2012; Littell et al., 2018; Westerling, 2018; Westerling et al., 2011; Westerling & Bryant, 2008), less has been done to evaluate observed seasonal trends in fire‐relevant climate variables and whether these trends are consistent with those expected to arise from anthropogenic climate change. Here we provide a comprehensive empirical assessment of the observed effects of climate variability and change on California wildfire by season, region, and land cover. We first use wildfire and climate data within California to evaluate trends in seasonal burned area by region during 1972–2018, resolve the distinct seasonal and regional influences of climate and weather factors, and assess the stationarity of the dominant fire‐climate relationships over the past five decades. We then use climate model simulations to determine whether observed trends in the climate variables most pertinent to regional wildfire activity are consistent with expectations of anthropogenic climate change. A thorough and nuanced understanding of how, when, and where anthropogenic climate change has or has not affected wildfire in California over the past several decades is critical to guide sustainable societal decisions ranging from where to develop housing to how limited resources can be optimized for landscape management.

4 Conclusions

California has been the geographic focus of extensive speculation among scientists, politicians, and media as to the biophysical and societal factors that have contributed to recent exceptional wildfires and large increases in wildfire activity in recent decades (e.g., Krieger, 2018; Pierre‐Louis, 2018; Vore, 2018). Anthropogenic climate change is commonly debated as a driver of these recent wildfire changes, but there are many ways in which anthropogenic climate change could conceivably affect wildfire and many variables that wildfire in California is sensitive to. A nuanced understanding of how, when, where, and why California wildfire activity has increased in recent decades is critical for sustainable environmental and development decisions that specifically take into account how anthropogenic climate change is likely to proceed and affect wildfire across California's diverse landscapes. Our methods should be increasingly applicable to other regions globally, as governmental and satellite‐based records of wildfire activity are steadily alleviating observational duration as a major limiting factor for empirical studies of wildfire.

In this study we evaluated the various possible links between anthropogenic climate change and observed changes in California wildfire activity across seasons, regions, and land cover types since the early 1970s. The clearest link between California wildfire and anthropogenic climate change thus far has been via warming‐driven increases in atmospheric aridity, which works to dry fuels and promote summer forest fire, particularly in the North Coast and Sierra Nevada regions. Warming has been far less influential on summer wildfire in nonforest areas. In fall, the drivers of wildfire are particularly complex, but warming does appear to enhance the probability of large fall wildfires such as those in 2017 and 2018, and this effect is likely to grow in the coming decades.

Importantly, the effects of anthropogenic warming on California wildfire thus far have arisen from what may someday be viewed as a relatively small amount of warming. According to climate models, anthropogenic warming since the late 1800s has increased the atmospheric vapor‐pressure deficit by approximately 10%, and this increase is projected to double by the 2060s. Given the exponential response of California burned area to aridity, the influence of anthropogenic warming on wildfire activity over the next few decades will likely be larger than the observed influence thus far where fuel abundance is not limiting.

Below, we conclude with executive summaries of our primary findings for summer wildfire in forests, summer wildfire in nonforests, and fall wildfire.

4.1 Summer, Forest

Annual statewide burned area increased significantly during 1972–2018, largely due to an eightfold increase in annual summer forest‐fire extent, most of which occurred in the heavily forested North Coast and Sierra Nevada regions. Summer forest‐fire extent is strongly dictated by heat and atmospheric aridity, which reduce snowpack and dry out fuels. Warm‐season atmospheric aridity (vapor‐pressure deficit) increased significantly across California since the late 1800s, driven largely by daytime warming of approximately 1.8 °C (1.4 °C since the early 1970s). Based on a regression analysis, the vast majority of the observed increase in summer forest‐fire extent since 1972 is accounted for by observed significant increases in warm‐season vapor‐pressure deficit (caused by warming). Importantly, the sensitivity of burned area to aridity is modulated by background conditions such as fuel abundance and connectivity, ignition frequency, and resources dedicated toward suppression, all of which changed over the past century. However, the statistical relationship between vapor‐pressure deficit and forest fire area remained stable during 1972–2018, supporting the interpretation that increased aridity was the primary driver of the increase in summer forest‐fire area during this time. The observed rates of warming and increasing vapor‐pressure deficit are consistent with those simulated by climate models when forced by anthropogenic emissions, indicating that these trends are extremely likely to continue for decades to come. The large increase in California's annual forest‐fire area over the past several decades is very likely linked to anthropogenic warming.

4.2 Summer, Nonforest

Annual summer burned area did not increase in nonforest lands in the Central and South Coast regions, and increases in nonforest burned area were weak in the North Coast and Sierra Nevada. Summer nonforested burned area is most strongly promoted by high precipitation total in the year or two prior to the fire year, reflecting the necessity of precipitation for growth of fine fuels that can facilitate fire spread in the subsequent year. Fire‐year precipitation deficit and atmospheric aridity also appear to promote summer wildfire in these regions, but this effect is relatively weak. Over the past century, the frequency of wet years followed by dry years increased, which should have promoted nonforest summer wildfire. The lack of large increases in nonforest summer burned area may reflect the counteracting effects of the other factors such as human fire suppression, reduced ignitions, and reduced vegetation cover due to drought. Climate models do not represent the observed increase in interannual swings from wet to dry years as a robust result of anthropogenic climate change thus far. The link between anthropogenic climate change and summer wildfire in nonforest appears weak thus far.

4.3 Fall

Large fall wildfires became more frequent in California over the past several decades, mainly due to increases in the North Coast and Sierra Nevada regions. In all regions, large fall wildfires often occur when strong offshore wind events coincide with dry fuels. These conditions were extreme throughout California in 2017 and 2018, driving very large fall wildfires in all regions in one or both years. The character of offshore wind events did not change since records began in the mid‐1900s. Climate models project these wind events to decrease in frequency and intensity in the future. Fall fuel moisture is dictated largely by fall precipitation, but nonetheless is calculated to have declined significantly since the mid‐1900s due to warming. This warming‐induced drying was likely caused by a combination of anthropogenic forcing and natural multidecade variability and caused an 8‐day increase in the number of days per October–December with a high probability of large wildfires. This exemplifies an important secondary effect of background warming, which is projected to continue, on fall wildfires. In the South Coast, fall drying was also promoted by a small reduction in the frequency of fall precipitation, consistent with climate model projections. The link between anthropogenic climate change and fall wildfire appears weaker than in summer thus far but is likely to strengthen if continued warming and possibly delayed onset of winter precipitation counteract projected decreases in the intensity and frequency of offshore wind events.

Acknowledgments

All data sets used are publicly available, and the sources are listed in Table S1. A.P.W. was funded by Columbia University's Center for Climate and Life and the Zegar Family Foundation. We also acknowledge support from University of California Office of the President MRPI grant MRP‐17‐446315 (D.L., A.G., and J.G.M.), from NOAA via the CNAP RISA (D.L. and A.G.), from DOI via the Southwest Climate Adaptation Science Center grant G18AC00320 (A.G. and J.G.M.), the Visiting Scholar Program and Fire Centre Research Hub at the University of Tasmania (J.T.A.), Earth Lab through CIRES and the University of Colorado, Boulder's Grand Challenge Initiative (J.K.B.), and the USGS North Central Climate Adaptation Science Center (J.K.B.). LDEO publication 8332.