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Climate Change and the Character of Southern California Wildfires

Wildfire is a natural environmental phenomenon and has been an integral part of eco­systems in California for millennia. Yet although they are essential to the survival of several species, wildfires can be very destructive with implications for human health, housing, and infrastructure.

Wildfires that are low in intensity remove low-growing underbrush, clean the forest floor of debris, nourish the soil, kill pests, and keep the forest healthy. Some trees and plants require heat to open and release seeds for regeneration and even encourage wildfires by having leaves that are covered with flammable resins. 

However, in recent decades the numbers, severity, and area burned by Southern California wildfires have increased. Their impact on different niches of social and ecological systems and their toll on the state’s finances are expected to increase with climate change, population growth, and expanding development.

In the recently published paper titled Identification of two distinct fire regimes in Southern California: Implications for economic impact and future change scientists from UC Davis, UC Irvine, UCLA, the US Forest Service, and NASA's Jet Propulsion Laboratory made a collaborative effort to understand what drives wildfires, where they occur, what they destroy, and how high are the costs of the damage. For the time period 1990-2009 the researchers studied the wildfires that occurred in seven California counties: Santa Barbara, Ventura, Los Angeles, San Bernardino, Orange, Riverside, and San Diego. They classified the fires into two categories: very fast-spreading fires that typically occur closer to urban areas during Santa Ana winds in October through April (SA fires) and those that often occur in higher elevation forests during warm and dry periods in June through September (non-SA fires). SA fires usually expand to the west and northwest with a consumption rate (2703±1394 acres per hour) several times larger than that of non-SA fires, which typically expand to the east consuming 729±314 acres per hour. The results of joint research suggest that both, SA and non-SA fires will increase in their numbers, frequency and the area impacted by fire as a consequence of climate change.

The response of SA and non-SA fires to climate change during the middle part of the 21st century for the RCP8.5 scenario.

Development estimated by Jin et al. for wildfire features in response to climate change during the mid-21st century based upon the RCP8.5 scenario.

 

In a fact, Californians are already observing fire behavior that departs from the historical norm. For example, the recent Valley Fire in Cobb started as non-SA wildfire but it consumed 40,000 acres in only 12 hours at a rate (3’333 acre·h-1) comparable to consumption rate of SA fires. “None of us predicted, or could have predicted, how fast that fire moved,” Cal Fire spokeswoman Amy Head said on September 18th, 2015.

Interestingly, the two different fire types contribute nearly equally to the burned area, yet SA fires were responsible for 80% of cumulative 1990-2009 economic losses. Furthermore, the research findings indicate that non-SA fires could be stopped from spreading more effectively than the more dangerous SA fires. On the other hand increasing strength and frequency of non-SA fires may lead to an upslope shift of certain vegetation types, with implications for the montane forests in particular and for the whole ecosystem in general.

Post last edited on: 2015 October 02

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