With multiple wildfires raging throughout California, it is easy to wonder to what extent climate change may be to blame. Scientists are attempting to tackle this question, and to model what future fire regimes might look like as the climate changes, but there are few simple answers. As ecologists Jon Keeley and Alexandra Syphard put it in their recent article published in Geosciences, “Predicting future fire regimes is not rocket science; it is far more complicated than that.”
On a global scale, models generally predict increased fire activity as a result of a climate change. This is supported by historical links between fire and climate. In particular, higher temperatures and reduced precipitation lead to greater burned area by impacting fuel (vegetation) moisture and amount. Climate change models are not yet precise enough, however, to be useful for drawing local conclusions about future wildfire patterns. Local precipitation and temperature predictions still vary, and could end up forming new patterns that have few historical analogs. In addition, it is higher seasonal temperatures rather than higher average annual temperatures that are historically associated with higher burned area in certain regions, but current climate change models focus primarily on the latter.
Climate change will also indirectly affect fire activity by influencing vegetation patterns and plant productivity, further complicating future projections. A new analysis by researchers at South Dakota State University concludes that climate-induced vegetation change may increase fire frequency and size more than direct changes in temperature and precipitation. Another new study led by USDA Forest Service researchers concludes that fire severity could decrease across the western US by mid-century if vegetation changes track with the changing climate (e.g., denser vegetation is replaced with sparser, lower fuel volume plant communities in areas that become drier). They note that fire severity could temporarily increase, though, as others have predicted under static plant community scenarios, if fire suppression or other factors serve to delay plant community transitions.
In the end, Keeley and Syphard point out that there are other human forces at play as well that could prove even more important than climate change in determining future fire regimes. For instance, human population growth (and thus more fire ignitions) and land management decisions could be very influential in some landscapes.
Photo: Die-off of ponderosa pines in the southern Sierra Nevada Range in July 2016, following years of severe drought and high pathogen activity, both exacerbated by climate change. High tree density from more than a century of fire suppression also influences the area's susceptibility to wildfire and complicates calculating the size of global warming's influence. Photo by Jon E. Keeley from Keeley and Syphard, 2016.