Abstract
Extreme wildfires extensively impact human health and the environment. Increasing vapour pressure deficit (VPD) has led to a chronic increase in wildfire area in the western United States, yet some regions have been more affected than others. Here we show that for the same increase in VPD, burned area increases more in regions where vegetation moisture shows greater sensitivity to water limitation (plant-water sensitivity; R2 = 0.71). This has led to rapid increases in human exposure to wildfire risk, both because the population living in areas with high plant-water sensitivity grew 50% faster during 1990–2010 than in other wildland–urban interfaces and because VPD has risen most rapidly in these vulnerable areas. As plant-water sensitivity is strongly linked to wildfire vulnerability, accounting for ecophysiological controls should improve wildfire forecasts. If recent trends in VPD and demographic shifts continue, human wildfire risk will probably continue to increase.
Highlights
Extreme wildfires extensively impact human health and the environment
We consider the effects of climate on LFMC through a climate-derived moisture balance that considers both precipitation and vapour pressure deficit (VPD, calculated using the wetness of dead foliage and twigs in the litter; see Methods)
For different bins of plant-water sensitivity (PWS), spatially disparate locations with similar PWS are combined and the interannual variations of burned area and VPD is calculated across these locations (Fig. 1a)
Summary
Extreme wildfires extensively impact human health and the environment. Increasing vapour pressure deficit (VPD) has led to a chronic increase in wildfire area in the western United States, yet some regions have been more affected than others. The effect of atmospheric aridity on LFMC is regulated by a range of location-specific factors, including, but not limited to, topographic and soil controls on root-zone water availability, root water uptake and plant hydraulic traits that affect transpirational water loss. For the same meteorological conditions (including both atmospheric aridity and precipitation), fuel moisture can vary widely, depending on plant species and hydraulic diversity[23,24,25]. To assess whether current vegetation distributions will buffer or exacerbate future fire vulnerability in the western US, we test the interactions between PWS and other drivers of fire risk, including the rate of change in atmospheric aridity across the region, and the rate of growth of the WUI population
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