Last fall witnessed numerous devastating wildfires occurring across Australia, California, and other western states. For the most part, these conflagrations are much larger and more dangerous than the fires that burn in the eastern part of the country. This is due to a number of factors relating to the topography, climate, and the vegetation that fuels these blazes. For a fire to burn, it needs a source of heat, oxygen, and a fuel to burn. Firefighters refer to these three elements (heat, oxygen, fuel) as the “fire triangle.” When one of the components of the fire triangle is missing, the fire will not occur. Conversely, when these ingredients are present in abundant supply, the fire will be large and burn intensely. Southern California has been a source of many terrible wildfires of late. This area is characterized by warm, dry climatic conditions, strong winds arising from the mountain ranges and ocean breezes, and having vegetation that can ignite quickly and burn intensely.

The infamous Santa Ana winds affect this region in the late summer and fall. These strong, dry winds blow from the mountains towards the ocean, quickly drying out vegetation and woody material, adding abundant oxygen, and fanning the flames of any fire that might be burning. The west is also characterized by mountainous terrain that is steep and rugged, with its own weather patterns, as heated air rises during the day and cool air descends at night. The western United States is prone to many storm events where there are high winds, lightning and thunder, but little rain. Lightning strikes are a major cause of many wildfires in the western states, unlike the east where storm events usually include rain.

The drier conditions found in the western states favor vegetation such as evergreen trees that can withstand arid conditions. Much of this vegetation has volatile chemicals in their waxy needles, leaves, twigs, and woody tissue. Vegetation such as pine, spruce, cedar, sage brush, and laurel can easily ignite and burn very intensely given the proper conditions.

The west also has large sections of forest that are not impacted by humans due to steep slopes, remoteness, or an overall management strategy that prohibits any type of disturbance. The net result is that large amounts of dead and dying trees accumulate in these forests, adding greatly to the potential fuel load. Therefore, given the right conditions, a fire can start in a remote area on steep landscape, grow in intensity as the dried fuels burn and living vegetation ignites, and is spread quickly by convectional currents and the prevailing winds. All of these factors create extreme fire behavior.

Now aware of these dangers, many western communities are beginning to take steps to mitigate the fire hazard. Building homes with inflammable materials, installing sprinkler systems around the home, maintaining safe zones around the home with little or no vegetation, reducing fuel loading by thinning forests and removing dangerous fuels, improving access into communities, and maintaining well trained and equipped wildfire fighting specialists are some of the measures being taken to reduce the likelihood of devastating fires.

Article by FCFCDB

Page header photo credit: sciencemag.org - Kyle Grillot

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