Wind Drives All Large Blazes
– by George Wuerthner
As large fires have spread across the West in recent decades, we hear increasing demands to reduce fuels—typically through logging. But logging won’t reduce the large fires we are experiencing because fuels do not drive large fires.
You can have tons of fuel per acre as occurs in Oregon’s Coast Range or the Olympic Mountains of Washington, and have virtually no fires because they are too wet to burn. On the other hand, we have seen some huge acreage charred on overgrazed grasslands that have little more than stubble to burn if there is a major drought and wind.
What makes the difference is not the available fuel, but the climatic/weather conditions. Logging forests does not change the climate/weather.
The ingredients found in all large blazes include low humidity, high temperatures, and drought. Assuming you have these factors, you can get an ignition if lightning strikes. But even an ignition won’t lead to large fires.
The final ingredient in all large blazes is wind.
Wind’s effect is not linear. In other words, increasing wind speed from 10 mph to 20 mph does not double fire spread, rather it leads to exponential fire growth and increases the burn intensity.
We all know this from common experience. Think about the smoldering campfire you have encountered on a wet morning. Pile on more wood, and the fire only goes out. But fan that struggling blaze, and it will leap into flames.
Most large fires have wind speeds of 30-50 mph or more. Wind makes fire fighting difficult since embers are blown miles ahead of the burning fire front. It is also the reason why wind makes fuel reduction projects ineffective.
Wind drives flames through and over fuel treatments. Even clearcuts with little or no fuel will not halt a wind driven fire. The wind driven fire just dances around and over any fuel breaks.
The biggest problem with fuel reductions is that one can’t predict where and when fires will occur. The likelihood of a wildfire will encounter a treated forest in the time scale when fuel reduction are effective is incredibly low.
The vast majority of acreage burning around the West are occurring in higher elevation forests like lodgepole pine and various fir species that naturally burn at infrequent intervals, often hundreds of years apart. As a consequence, a fuel treatment in such forests is a waste of time because the probability of a fire occurring at all in the time when fuel reductions are effectiveness is extremely low.
Even in drier forests like ponderosa pine that burn more frequently the chances that a fire will encounter a fuel treatment while it’s most effective is around 1-2%.
SO WHERE SHOULD FUELS TREATMENTS OCCUR?
There is a role for fuel reduction projects. The best ones are targeted near communities and other areas of interest. The idea being one cannot predict where a fire may start, but one can predict what you don’t want to burn up in a fire. So focus fuels reductions adjacent to those places.
The most important fuel reduction projects should occur in the communities themselves. Removal of wood piles from adjacent to homes. Clearing pine needles from roofs. Getting rid of flammable building materials like cedar shake roofs.
Reducing the flammability of homes are the kinds of “fuel reductions” that work and should be encouraged. If these fuel reductions were implemented religiously, we wouldn’t have to worry about wildfires in the hinterlands, and we could permit these blazes to do the important ecological work they perform without continual interference from humans, yet feel secure in the knowledge that our communities were safe from wildfires.
George Wuerthner is an ecologist and former hunting guide with a degree in wildlife biology.