摘要：Increases in vapor pressure deficit (VPD) have been hypothesized as the primary driver of future fire changes. The Coupled Model Intercomparison Project Phase 5 (CMIP5) models agree that western U.S. surface temperatures and associated dryness of air as defined by the VPD will increase in the 21st century for Representative Concentration Pathways (RCPs) 4.5 and 8.5. However, we find that averaged over seasonal and regional scales, other environmental variables demonstrated to be relevant to flammability, moisture abundances, and aridity—such as precipitation, evaporation, relative humidity, root zone soil moisture, and wind speed—can be used to explain observed variance in wildfire burn area as well or better than VPD. However, the magnitude and sign of the change of these variables in the 21st century are less certain than the predicted changes in VPD. Our work demonstrates that when objectively selecting environmental variables to maximize predictive skill of linear regressions (minimize square error on unseen data) VPD is not always selected and when it is not, the magnitude of future increases in burn area becomes less certain. Hence, this work shows that future burn area predictions are sensitive to what environmental predictors are chosen to drive burn area. Plain Language Abstract Since the 1980s, the western United States (U.S.) has warmed and wildfire burn area has increased. Most global climate models agree that the western United States will continue to warm and dry. If wildfire activity and aridity continue to change together in ways similar to the recent past, western U.S. fire activity will continue to dramatically increase through the 21st century. Global climate models are less certain regarding how other wildfire relevant environmental conditions may change. This work objectively selects linear combinations of wildfire‐relevant environmental conditions that best explain historical variability in western U.S. wildfire burn area. We then use climate model output to estimate how future wildfire burn area might change, as predicted by the objectively selected variables. We show that increases in burn area are likely as many climate models suggest the future will be drier. However, we find that future wildfire burn area estimates are lower whenever and wherever the importance of aridity is reduced.
