I ran across this interesting approach to western fires from NASA. Followers of this blog have read the fire observations of folks like Leiburg in the teens, in which the Native American burning patterns were still visible. Then came big fires and fire suppression efforts, and since 1950 many changes in forest and fire management, invasive species, people living in the forest, people igniting the forest and so on. So to me, anyway, picking the dates 50 til present is within that larger dynamic and understanding the larger dynamic could explain some of the observations.
Data sources for the study are given at the end of the article.
1. There are more fires.
Over the past six decades, there has been a steady increase in the number of fires in the western U.S. In fact, the majority of western fires—61 percent—have occurred since 2000 (shown in the graph below).
(I think we’ve talked about the historic fire databases before.)
2. And those fires are larger.
Those fires are also burning more acres of land. The average annual amount of acres burned has been steadily increasing since 1950. The number of megafires—fires that burn more than 100,000 acres (156 square miles)—has increased in the past two decades. In fact, no documented megafires occurred before 1970.
(This is interesting, even if only from 1950 to 1970. It’s not clear to me what the frequency is on the y axis of this graph).
3. A small percentage of the West has burned.
Even though fire frequency and size has increased, only a small percentage of western lands— 11 percent—has burned since 1950. In this map, wildfires are shown in orange. Private lands are shown in purple while public lands are clear (no color). The location of wildfires was random; that is, there was no bias toward fires affecting private or public land.
Keith Weber, a professor at Idaho State University who led the analysis, was surprised at the 11 percent figure. There’s no clear reason yet for why more of the region hasn’t burned. “Some of the 89% may not burn because it has low susceptibility—not dry enough or it has low fuel (vegetation),” said Weber. “Some areas may be really ripe for a fire, but they have not had an ignition source yet.”
(I’m not sure about the public vs private land maps here.. check out the San Joaquin Valley of California. Also not sure if Tribal lands are considered public or private).
4. The same areas keep burning.
How has only 11 percent of the west burned, yet the annual number of acres burned and the frequency of fire increased? It turns out that many fires are occurring in areas that have already experienced fires, known as burn-on-burn effects. About 3 percent—almost a third of the burned land—has seen repeated fire activity.
The map here shows the locations of repeated fire activity. While you can’t see it at this map’s resolution, some areas have experienced as many as 11 fires since 1950. In those areas, fires occurred about every seven years, said Weber, which is about the amount of time it takes for an ecosystem to build up enough vegetation to burn again.
(It would be interesting to know exactly where those are).
5. Recent fires are burning more coniferous forests than other types of landscape.
Since 2000, wildfires have shifted from burning shrub-lands to burning conifers. The Southern Rocky Mountains Ponderosa Pine Woodland landscape has experienced the most acres burned—more than 3 million.
(Again, this is very interesting but not clear on what it means. Certainly plenty of shrublands are still burning.)
6.Wildfires are going to have a big impact on our future.
Research suggests that global warming is predicted to increase the number of very large fires (more than 50,000 acres) in the western United States by the middle of the century (2041-2070).
The map below shows the projected increase in the number of “very large fire weeks”—periods where conditions will be conducive to very large fires—by mid-century (2041-2070) compared to the recent past (1971-2000). The projections are based on scenarios where carbon dioxide emissions continue to increase.
(This assumes that more bad fire weather=more bad fires. That’s not a bad assumption (projections of future weather changes based on unknown levels of carbon) but reasonable people could also include assumptions about improvements in firefighting, community resilience, warming causing plant life to grow more slowly and lead to lower fuel loadings at less density, and so on.). It’s a bit like predicting deaths from a disease without considering health care efforts.