Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring
Open accessAbstract
Prior work shows western US forest wildfire activity increased abruptly in the mid-1980s. Large forest wildfires and areas burned in them have continued to increase over recent decades, with most of the increase in lightning-ignited fires. Northern US Rockies forests dominated early increases in wildfire activity, and still contributed 50% of the increase in large fires over the last decade. However, the percentage growth in wildfire activity in Pacific northwestern and southwestern US forests has rapidly increased over the last two decades. Wildfire numbers and burned area are also increasing in non-forest vegetation types. Wildfire activity appears strongly associated with warming and earlier spring snowmelt. Analysis of the drivers of forest wildfire sensitivity to changes in the timing of spring demonstrates that forests at elevations where the historical mean snow-free season ranged between two and four months, with relatively high cumulative warm-season actual evapotranspiration, have been most affected. Increases in large wildfires associated with earlier spring snowmelt scale exponentially with changes in moisture deficit, and moisture deficit changes can explain most of the spatial variability in forest wildfire regime response to the timing of spring. This article is part of the themed issue ‘The interaction of fire and mankind’.
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In the western United States, fire-season length has increased by 34% (from 166 to 222 days), ultimately leading to increased annual area burned.
“An example is in the western United States, where the fire-season length has increased by 34% (from 166 to 222 days), ultimately leading to increased annual area burned (Westerling, 2016).”
From Fire as a fundamental ecological process: Research advances and frontiers (2020) · cites this paper as Westerling, 2016
Table 3 (Discussion) reports fire-season lengths of 166 days in 1983–1992 and 222 days in 2003–2012 for five western forest areas—an increase of about 34%. The trends section also reports increased forest area burned, but attributes that increase in part to more frequent large fires; it does not establish that the longer fire season led to the increase in annual area burned. (LLM, conf=0.86)
Experimental — accuracy not yet measuredIncreases in wildfire have been observed for both forest and grassland wildfire.
“and increases have been observed for both forest and grassland wildfire (Westerling, 2016)”
From Wildfire Induces Changes in Receiving Waters: A Review With Considerations for Water Quality Management (2022) · cites this paper as Westerling, 2016
In the western United States, evidence indicates that warming and drying, including from human-caused climate change, are associated with more frequent and larger fires and longer fire seasons.
“In the western United States, there is strong evidence that regional warming and drying, including that directly attributed to anthropogenic climate change, are linked to increased fire frequency and size and longer fire seasons (5–9).”
From Human-started wildfires expand the fire niche across the United States (2017) · cites this paper as [7]
The growth in large western US fires is probably caused by climate and fuel changes, not ignition sources.
“This finding is consistent with other studies that have demonstrated an increase in large fires across the western United States (6, 7, 40), likely as a consequence of changes in climate and fuels rather than ignitions.”
From Human-started wildfires expand the fire niche across the United States (2017) · cites this paper as [7]
Over recent decades, warmer and drier conditions beginning earlier have increased fire activity in the western United States.
“In the past few decades, early onset of warmer and drier conditions has promoted greater fire activity across the western United States (6, 7, 40).”
From Human-started wildfires expand the fire niche across the United States (2017) · cites this paper as [7]
Forest fires release CO2 into the atmosphere, which in turn increases the rate of forest fires.
“Besides their potential for harming people and property, forest fires release CO 2 into the atmosphere (which in turn increases the rate of forest fires [839]).”
From Tackling climate change with machine learning (2023) · cites this paper as [839]
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- Authors
- Westerling, A. L.
- Affiliations
- University of California, Merced (US)
- Corresponding author
- Westerling, Anthony LeRoy
- Venue
- Philosophical Transactions of the Royal Society B: Biological Sciences
- Publisher
- The Royal Society
- Published
- 2016-06-05
- Volume
- 371
- Issue
- 1696
- Pages
- 20150178
- ISSN
- 0962-8436 (ISSN-L)
- 1471-2970
- PMC
- PMC4874415
- OpenAlex
- W2401580071
- Cited by
- 1,322
- References
- 23
- Citations by year
- 2026: 113 · 2025: 129 · 2024: 165 · 2023: 156 · 2022: 199 · 2021: 166 · 2020: 134 · 2019: 102 · 2018: 85 · 2017: 57 · 2016: 15
- FWCI
- 63.86
- Type
- journal article
- Language
- en
- Update notices
- correction (2016-11-05)
- Open access
- bronze
- doi.org
- Locations
- Philosophical Transactions of the Royal Society B Biological Sciences (publishedVersion)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- eScholarship (California Digital Library) (submittedVersion)
- NOAA Institutional Repository (submittedVersion, public-domain)
- Funders
- National Oceanic and Atmospheric Administration (NA110AR4310150)
- Topics
- Physical Sciences › Environmental Science › Global and Planetary Change › Fire effects on ecosystems
- Physical Sciences › Environmental Science › Global and Planetary Change › Plant Water Relations and Carbon Dynamics
- Physical Sciences › Environmental Science › Global and Planetary Change › Forest Management and Policy
- Keywords
- forest fires, wildfire regimes, moisture deficit, evapotranspiration, burned area, Rocky Mountains, western United States forests, climate change
- MeSH terms
- Fires, Seasons, Time Factors, Trees, United States, Forests
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