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Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring

Highlights prior work on wildfires that show western US forest wildfire activity increased abruptly in the mid-1980s, and that large forest wildfires and areas burned in them have continued to increase over recent decades, with most of the increase in lightning-ignited fires
Holds that wildfires in the Northern US Rockies dominated early increases in wildfire activity, and still contributed 50% of the increase in large fires over the last decade
Finds, however, the percentage growth in wildfire activity in Pacific northwestern and southwestern US forests has rapidly increased over the last two decades
Finds wildfire numbers and burned area are also increasing in non-forest vegetation types
Finds wildfire activity appears strongly associated with warming and earlier spring snowmelt
Analyzes the drivers of forest wildfire sensitivity to changes in the timing of spring, which demonstrates that forests at elevations have been most affected (these regions are where the historical mean snow-free season ranged between two and four months, with relatively high cumulative warm-season actual evapotranspiration)
Finds that 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
Figure:
Human and lightning-ignited annual large forest fires, (a), grass and shrubland fires (b), forest burned area (c), and grass and shrub burned area (d), on Forest Service, Park Service and Indian Lands in the western US. Horizontal lines indicate decadal averages.

Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring

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