Tag: statistics

Regular readers of Wildfire Today know that I like to present statistics, charts, and graphs about wildland fire size and occurrence. The first article on Wildfire Today on this topic was in January 19, 2008, and the last time was December 10, 2010. The final numbers for the 2010 calendar year for the United States are available, and I found a new source for crunching data, Many Eyes. So, there’s a new excuse reason for writing another article.

One statistic I concentrate on is the average size of fires, not so much the number of fires or the total acres burned each year, two stats that the mainstream media harps on. The average size is affected not only by the weather, but also by the fuel condition and age, how many fires were burning at the same time, the short-term availability of firefighting resources, the skill and efficiency of the firefighting effort, strategy used on fires, and the number of firefighting resources on the payroll of the firefighting agencies.

Here are a few new ways of visualizing the average size of wildland fires, in acres, in the United States, from 1960 through 2010. The data for the number of fires and acres burned each year came from NIFC. Then I spent some time with Excel and Many Eyes to develop these products.

And the standard stack graph:

The average fire size in 2010 was 48 acres, compared to the average between 1960 and 2010 which was 37.

The chart below shows the average size of wildfires in the United States by decade.

We have been tracking the fire occurrence stats provided by the National Interagency Fire Center for several years. It is clear that the average size of fires has been increasing since 1970 while the average number of fires is decreasing.

We are having fewer, but larger fires. While the population in the country continues to grow, a person might think that the number of fires would increase. But some of the other factors that come into play are fire prevention programs and better technology for preventing fires.

There will be debate about why fires are larger. Climate change will be first on many people’s minds, but we must also consider the build-up of fuels as a result of fire suppression over the last 100 years. The chickens are coming home to roost.

This increase in fire size comes in spite of better management and technology in reporting fires, communications, water handling, incident management, and dispatching.

But better technology and management have their limits when it comes to putting out a massive fire. Large wind or fuel driven fires can only be followed by firefighters. We can chip away at the flanks or suppress the heel, but we can’t stop the forward progress of a raging fire until something changes…. the weather or the fuel. Or, as proven by Bill Molumby’s incident management team on the Indians fire east of Big Sur this summer, you have the luxury of time, distance, and very little private land, and you can backfire or burnout miles ahead of the fire.

The glamorous toys that politicians and extremist talk radio hosts clamor for (I’m talking to YOU, Roger Hedgecock and San Diego) such as water-scooping air tankers and night flying helicopters have their use, but they are totally ineffective in strong winds, when we are most likely to be losing homes and citizens. It can be too dangerous for pilots to fly under those conditions, and the retardant and water that is dropped is completely dispersed before it hits the ground.

We all know that wildland fires are larger than they used to be. Almost every summer recently there are fires that exceed 100,000 acres. Before 1990 this was not common.

I analyzed some fire occurrence statistics obtained from the National Interagency Fire Center and the National Incident Information Center. The numbers for 2007 are through November 4, 2007. Usually when fire occurrence statistics are displayed you will see total acres and the number of fires by year. But when I computed the average size of fires for each decade, the 1970s through 2007, a trend is painfully obvious. During those four decades the average size of fires increased by 400%, while the average number of fires each year decreased by 44%. (Click on the graphs to make them larger.)

But why are fires larger? Some of the factors that could cause such an increase in the average size are:

• Fire suppression for the last 100 years is catching up with us. Preventing naturally occurring fires to routinely reduce the fuel loads increases the amount of fuel, and the continuity of it, available when a fire starts. Fires burn more intensely and with more resistance to control.
• Climate change. There is no doubt that temperatures in the last few decades have been higher that they were before this period. We can debate how this may have affected wildland fires. Many areas have had extended droughts, causing die back of brush and shrubs. Trees are stressed, making them more susceptible to insects and other pests. Do these higher temperatures have a direct effect on fire behavior on an hour by hour basis?