From The Conversation, a new open access journal which allows article reproduction under a Creative Commons license [Bravo! — esnl], a very important article from University of California, Merced, Associate Professor of Environmental Engineering Anthony LeRoy Westerling:
Dramatic images of out-of-control wildfires in western North American forests have appeared on our television and computer screens with increasing regularity in recent decades, while costs of fire suppression have soared. In 2015, federal spending on suppression exceeded US$2 billion, just 15 years after first exceeding $1 billion. Something has been changing our fire seasons.
There are competing explanations for why wildfires have been increasing, particularly in our forests. I’ve been studying the science of climate and wildfires for more than 15 years and the take-home message from our research is that, while our management of the landscape can influence wildfire in many different ways, it is a warming climate that is drying out western U.S. forests and leading to more, larger wildfires and a longer wildfire season.
A look at the latest data
Ten years ago, several colleagues and I set out to see if we could quantify the changes in wildfire, particularly in mountain forests of the western U.S. We wanted to see if climate might be causing some of the increase in wildfire.
In our paper, we concluded that wildfire had indeed increased substantially in western U.S. forests beginning in the 1980s. We also found that most of this increase was from fires burning primarily in mid-elevation northern U.S. Rocky Mountain forests in years with an early snowmelt.
Our latest research shows that wildfire activity in western U.S. forests has continued to increase, decade by decade, since the 1980s.
We looked at federally managed forests in the Sierra Nevada, Southwest, Pacific Northwest, and northern and southern Rockies. Over the decade through 2012, large fires (fires greater than 1,000 acres or 400 hectares) were 556 percent more frequent than in the 1970s and early 1980s. And the area affected increased even more dramatically: the forest area burned in large fires between 2003 and 2012 was more than 1,200 percent greater than in the period between 1973 and 1982.
New “hot spots” for forest wildfire have also emerged.
The area burned in the northern U.S. Rockies has increased by 3,000 percent, accounting for half of the increase in the western U.S. But fire activity has recently accelerated in Southwest and Pacific Northwest forests as well. The area of burned forest in the Southwest increased over 1,200 percent, and in the Northwest by nearly 5,000 percent.
The only forest area where we could not robustly detect an increase in large fires and burned area was in coastal southern California. There, the largest fires are human-ignited, take place in the fall (driven by Santa Ana winds) and burn primarily in chaparral or shrubland. The small number of forest fires in southern California, combined with high variability from year to year, meant we could not detect trends there, nor attribute them to specific causes.
At the same time, the number of large fires in the West and the area they affect have been increasing in drier, lower elevation grass and shrublands, although to a much lesser extent. For example, the area burned in nonforest vegetation in lands managed by several federal agencies (the Forest Service, Park Service and Bureau of Indian Affairs) has been increasing about 65 percent per decade as compared to the 1970s average, for the past three decades.
The sharp increase in the amount of land being burned in recent decades across all vegetation types is not just due to more wildfires.
In fact, the total number of reported wildfire ignitions does not appear to have gone up. However, the number of large (greater than 1,000 acres or 400 hectares) wildfires has been growing since the 1980s, and the area burned in these fires has grown even more. Wildfires, in other words, are growing in size.
The length of the fire season has also grown throughout the last four decades, with large fires igniting earlier in the spring and later in the autumn than previously, and burning for longer. In the period between 2003 and 2012, the average burn time for individual fires was 52 days. In the 1973-1982 period, it was just six days.
There’s a whole lot more, after the jump. . .