Local winds play key role in some megafires

Localized winds sometimes play a much larger role.

The 2014 King Fire. Credits: USFS
The 2014 King Fire. Credits: USFS

According to an estimate, wildfires have burned 4,200 square miles in the United States this year. The reason behind this fire is drought and overgrown forests. But by further examining it by using NASA before-and-after data, scientists found that the localized wind plays an important role in creating large, destructive fires.

The study mainly focused on 2014 King Fire, using data from airborne instruments managed by NASA’s Jet Propulsion Laboratory in Pasadena, California. For details, scientists used advanced computer simulations from NCAR. The King Fire was a wildfire that scorched over 97,000 acres (390 km2) of land.

Scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado have conducted this study, where they found that winds — both very localized winds related to topography and winds created by the searing heat of the flames — were the reason the fire suddenly ran 15 miles (24 kilometers) up a steep canyon one afternoon. Sometimes, these winds go undetected.

NCAR scientist Janice Coen, the lead author of the study said, “This brings into question several widely held and largely unquestioned assumptions, such as very large fires being caused by the accumulation of vegetation, persistent dry conditions, or requiring extreme conditions. In the King Fire, small-scale winds and winds generated by the fire had a much greater impact on this fire, and potentially others like it, than any of the other factors.”

JPL scientist Natasha Stavros, a coauthor on the study, said, “The NASA airborne measurements were unique in that we observed the forest’s vertical structure before and after a fire. These observations let us better identify the type of fuel — grass, shrubs, or trees. That improved the model simulations, particularly of how the fire spread in areas where previous fires had burned or timber had been as harvested, and in areas where the burn severity was greatest.”

Scientists reported that this data has offered them an opportunity to recreate an actual wildfire within a sophisticated NCAR computer model that combines weather prediction and fire behavior, testing the importance of different factors.

The scientists concluded that the fire became stronger in the canyon because of the inclined slopes. Drought conditions or increased vegetation did help the fire to generate the strong updraft that drew flames up the canyon slope.