It’s been a bad year for California, not helped by drought conditions. So far the state has seen 3,381 wildfires in California covering 15,055 acres in 2015. The five-year average is 2,256, according to the California Department of Forestry and Fire Protection.
The US as a whole has seen 32,400 fires so far this year, covering 5.4 million acres. Last year there were 29,812 fires spread over 1.1 million acres, according to the National Interagency Fire Center.
Early warnings for wildfires may come from forecasting stratospheric intrusions, winds that bring dry air from the upper atmosphere to the surface, according to a new study from the National Oceanic and Atmospheric Administration (NOAA).
Fires in May 2013 were used to provide data for the study, which found that extremely dry air, very high in ozone, reached the surface of southern California. The dry air concentration occurred just before the fires broke out, burning 25,000 acres north-west of Los Angeles.
‘The atmosphere could give us an early warning for some wildfires,’ says Andrew Langford, a research chemist at NOAA Earth System Research Laboratory in Boulder, Colorado.
‘Stratospheric intrusions are double trouble for Southern California,’ says Langford. ‘We knew that the intrusions can add to surface ozone pollution. Now we know that they also can contribute to the fire danger, particularly during La Niña years when deep intrusions are more frequent, as recently shown by our NOAA colleagues at the Geophysical Fluid Dynamics Laboratory. The good news is that with models and observations, we can get an early warning from the atmosphere in some cases.’
Meanwhile, an illegal campfire in Stanislaus National Forest, adjacent to Yosemite National Park that started the third largest fire in California’s history back in 2013, had provided researchers with new information on how forests recover from wildfires.
‘We would never be able to do an experiment on this, never be able to burn the forest in this way, so this natural experiment is a perfect opportunity to see what happens,’ says Alan H. Taylor, Professor of Geography at Penn State.
‘If a forest burns every ten years, ponderosa pine is pretty fire resistant,’ says Lucas Harris, a graduate student who worked on the project. ‘But after 100 years of fire suppression, there are a lot of pine needles on the forest floor and they are highly flammable. We found areas of ponderosa pine burned more severely than areas with other trees.’
In the early 1900s, the US Forest Service had a policy of total fire suppression in their forests. ‘Fuels and terrain were the major factors contributing to the severity of the forest fire,’ says Harris. ‘The only one of these that can be controlled is the fuel.’
Some forest areas have not burned in 100 years, and that means workers have to manually remove plants, shrubs and small trees that can stimulate fire. ‘In pine forests where fires naturally occur every five to ten years, 100 years of fire exclusion creates an understory with abundant surface fuel and small trees that allow fires to move into the tree canopies,’ says Taylor. ‘Normally, with frequent fires, only the understory burns with some burn scarring of tree trunks, but the trees survive. However, in Big Oak Flat during the Rim fire, there was an unusually high proportion of moderate and high severity fires compared to 1899.’
The study’s findings are supported by research from the US Forest Service, which found that harvesting fire-killed trees can reduce fuels for future fires in dry coniferous forests. Fire-killed trees were previously logged for economic value, but not to prevent fuel build up for future fires.
‘In comparing logged and unlogged stands, we found that logged stands had higher fuels than unlogged stands, on average, during the first five years after fire and logging, but then had lower fuels from seven to 40 years after fire, with the greatest differences being found for large-diameter woody fuels,’ says Peterson.