Climate Change

Daily temperature extremes affect fire activity in Sierra Nevada: Study

Number of wildfires in the region could rise by as much as 83% by the 2040s; the area burned could climb 92%  

By DTE Staff
Published: Thursday 18 November 2021
Daily temperature extremes affect fire activity in Sierra Nevada, flags study. Photo: iStock

Fire has played a key role in the development of the biodiversity of the western United States. During the middle and latter half of the 20th century, a new fire regime of infrequent, high intensity fires was prevalent. Changing climate in the 21st century is expected to further modify ecosystem structure and function.

A new study titled Wildfire response to changing daily temperature extremes in California’s Sierra Nevada, published in Science Advances, shows that daily temperature plays a significant role in shaping fire behaviour during the summer in the Sierra Nevada eco-region in California. The hottest days during summer have a disproportionate and non-linear effect on fire activity.

About 30 per cent of the total increase in burned area from the 1980s through the 2010s can be attributed directly to increasing summer air temperature.

The study said:

Increasing daily summer temperature extremes will increase the number of fires by 51 ± 32 per cent and burned area by 59 ± 33 per cent through the 2040s relative to a 2011-2020 baseline. This means that the number of wildfires in the region could rise by as much as 83 per cent by the 2040s, and the area burned could climb by 92 per cent.

The researchers separated the summer into two periods (June-July and August-September) to reduce variation in temperature caused by seasonal trends.

The probability of wildfire occurrence in Sierra Nevada has a strong, highly significant positive relationship with daily temperature during both June-July and August-September summer intervals.

Daily burned area also has a strong, positive relationship with daily temperature during summer. A 1°C increase in daily temperature increases burned area by about 25.5 ± 0.7 per cent during June to July and 22.3 ± 0.8 per cent during August to September.

The strong positive relationships between daily temperature and fire activity are a consequence of warmer days drying fine fuels, which, in turn, increases the likelihood of successful ignition, fire escape from human control, and rate of fire spread, the researchers said.

The researchers looked at 441 fires larger than 100 acres between the period 2001–2020 in Sierra Nevada.

Most of the fires occurred during the hot and dry summer, with the four-month period from June 1 through September 30, accounting for more than 86 per cent of the annual number of fires and 94 per cent of the total annual burned area, according to data from the California Department of Forestry and Fire Protection’s Fire and Resource Assessment Program.

Fire occurrence and burned have increased considerably in the Sierra Nevada eco-region. Human-caused warming has already significantly enhanced wildfire activity in California, particularly in the forests of the Sierra Nevada and North Coast, and will likely continue to do so in the coming decades.

In the absence of changes in fire and ecosystem management, considerable potential exists for an increase in fire activity in the Californian region of Sierra Nevada.

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