USA — By 2050, wildfire seasons will be about three weeks longer, twice as smoky and wider in area, according to environmental research scientists at the Harvard School of Engineering and Applied Sciences (SEAS), in collaboration with the École Polytechnique Fédérale de Lausanne in Switzerland.
A study was commissioned by multiple federal agencies, the EPA, NASA, the NIH and other scientists who are trying to bridge the gap between NASA satellite and models and policymakers, said Loretta J. Mickley, a senior research fellow in atmospheric chemistry at SEAS. Mickley is co-author of the new study and has been working on the issue since 2008.
Mickley said the study mathematically predicts how gradual climate change may contribute in the coming years to increases in disruptive events, such as severe storms and forest fires, that depend heavily on meteorological factors.
We wanted to understand the relationships between weather and wildfire area burn so how big the fire given weather conditions, she said.
Wildfires are triggered mainly by human activity and lightning, but grow and spread according to the weather, which varies from region to region. To understand this better, Harvard researchers looked at 30-years worth of meteorological observations and records on area burned by wildfires in the west.
By looking at the 30 years of records, we were able to pull out relationships between fire, weather and areas burned, Mickley said.
Those relationships vary by region and by ecosystem. For example, in the heavily forested Rocky Mountains, the best predictor of a wildfire area is the amount of moisture in the forest floor from the previous summer, which depends on the temperature, rainfall and relative humidity that season. Mickley said these variants were studied and then Harvard researchers merged the data with the conclusions of the fourth Intergovernmental Panel on Climate Change (IPCC), which used socioeconomic scenarios to predict possible future atmospheric and climatological conditions.
Step two was to look at this ensemble of climate models and at the weather that these models told us would occur in the 2050s, she said. We wanted to get a hold on what future the temperature conditions would be.
By running the IPCCs climate data for 2050 through their own fire prediction models, the Harvard team was able to calculate the area burned for each eco-region at midcentury.
Our findings told us that higher temperature drive fire activity, Mickley said. All the data supported an increase in the west by, on average, during the fire season, of 4° to 5°F.
The calculations suggest for 2050 in the western U.S., the area burned in the month of August could increase by 65% in the Pacific Northwest compared to present-day conditions, nearly double in the Eastern Rocky Mountains/Great Plains regions and quadruple in the Rocky Mountains forest region. In addition, the probability of large fires could double or triple while the start date for the fire season could be earlier (late April instead of mid-May) and the end date later (mid-October instead of early October).
Mickley said the data also found number of large fires more than 1 mile square, would increase by double or perhaps triple by 2050. In addition, air quality is projected to suffer. Smoke from wildfires is composed of organic and black carbon particles and can impede visibility and cause respiratory problems, she said. Based on this information and known emission factors for combustion, the researchers predict that smoke will increase 20% to 100% by the 2050s more than double the rates currently.
The increase in smoke is an important climate penalty, a secondary affect, Mickley said. Our work suggests that even though the average temperature may be creeping up slowly we expect more sudden, big fires to occur in the future. We argue that this call for greater allocation of resources for forest management.