Some recent headlines (Yosemite wildfire leads to helicopter evacuations of about 100 visitors; Yosemite wildfire nearly quadruples in size) in the news might lead you to think that Yosemite National Park is being engulfed in flames. The fact is that in many of Yosemite’s ecosystems, fire is a natural part of the environment and allowing fire to burn under the right conditions is beneficial for these ecosystems. Fire managers in Yosemite have recognized this for decades and have been allowing fires ignited by lightening to burn in the backcountry and researchers like Brandon Collins (US Forest Service) and Scott Stephens (UC Berkeley) have been studying the effects. In fact, the time since the last fire is a major determinant of subsequent fire size since fire consumes biomass in the forest.
Why then did this recent fire make the news? Fire is in part driven by weather and this has been a dry year in California. When winds shift or wind speed increases, the rate at which fire spreads can change rapidly. In a place like Yosemite’s backcountry, rapid growth in fire size from changing winds can put people recreating at risk. Risk to people from wildfire presents a major challenge for land managers trying to restore this natural process.
It is important to realize that putting a fire out today does not diminish fire risk in the future in these fire-prone environments. As Brandon Collins and colleagues reported from their work in Yosemite, fire is a self-limiting process because the biomass (plants, leaves, branches, dead trees) that fuels the fire is consumed. When we suppress fires, that biomass continues to accumulate and can lead to the occurrence of very large wildfires, especially when extreme weather conditions occur.
Research by LeRoy Westerling (UC Merced) and colleagues has demonstrated the link between the increasing number of large wildfires and increasing temperature. Using the relationship between climate and wildfire, Westerling has made projections about the future of large wildfires in California as the climate changes. Their findings in a phrase – California is going to see more large wildfires.
While the fires individually pose a risk to society, their emissions also pose a serious risk to a much larger proportion of the population. Fires degrade air quality by emitting by-products that are harmful to humans. In a recent study, we used LeRoy’s results and projected the emissions from these wildfires under different climate change scenarios. By the end of this century, we project an increase of 19-101% in emissions from large wildfires. This could have substantial impacts on air quality in both California and Nevada, a topic we continue to research.
You’re probably wondering how managed or prescribed fires, like the one in Yosemite, impact air quality. Well the truth is they emit by-products that are bad for human health as well. However, they emit a lot less of the stuff. When Christine Wiedinmyer (NCAR) and I investigated this question, we found that managed or prescribed fire emissions could be as much as 60% lower than wildfire. The point we didn’t make in this paper is that land managers are very adept at managing fire so that smoke impacts on society are minimized. While these managed fires may impact us occasionally, it is important to remember that they provide many benefits for the ecosystems in which they are burning and help reduce the chance of future large wildfires.