Lately, it feels like we’re hearing about wildfires erupting in the western United States more often. But how have wildfire occurrences changed over the decades?
Researchers with the NASA-funded Rehabilitation Capability Convergence for Ecosystem Recovery (RECOVER) have analyzed more than 40,000 fires from Colorado to California between 1950 to 2017 to learn how wildfire frequency, size, location, and a few other traits have changed.
Here are six trends they have observed in the western United States:
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).
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.
Source: NASA RECOVER / Keith Weber
The recent increase in fire frequency and size is likely related to a few reasons, including the rise of global temperatures since the start of the new millennia. Seventeen of the 18 warmest years on record have occurred since 2001.
Global temperatures can affect local fire conditions. Amber Soja, a wildfire expert at NASA’s Langley Research Center, said fire-weather conditions—high temperatures, low relative humidity, high wind speed, and low precipitation—can increase dryness and make vegetation in the west easier to burn. “Those fire conditions all fall under weather and climate,” said Soja. “The weather will change as Earth warms, and we’re seeing that happen.”
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.”
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.
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.
The reason might lie within the tree species. Ponderosa Pine is a fire-adapted species. With its thick and flaky bark, the tree can withstand low-intensity surface fires. It also drops branches lower as they age, which deters fire from climbing up the tree and burning their green needles. “The fire will remove forest undergrowth, but will be just fine for the pines,” said Weber. “We are starting to see Ponderosa Pines thrive in those areas.”
Source: National Park Service
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.
According the Fourth National Climate Assessment, wildfires are expected to affect human health and several industries:
- Wildfires are expected to further stress our nation’s “aging and deteriorating infrastructure.”
- Smoke from wildfires is expected to impair outdoor recreational activities.
- Wildfires on rangelands are expected to disrupt the U.S.’s agricultural productivity, creating challenges to livestock health, declining crop yields and quality, and affecting sustainable food security and price stability.
- Increased wildfire activity is “expected to decrease the ability of U.S. forests to support economic activity, recreation, and subsistence activities.”
More about the source data:
Unless otherwise stated in the article, these data come from NASA’s Rehabilitation Capability Convergence for Ecosystem Recovery. RECOVER is an online mapping tool that pulls together data on 26 different variables useful for fires managers, such as burn severity, land slope, vegetation, soil type, and historical wildfires. In the past, fire managers might need several days or weeks to assemble and present such a large amount of information. RECOVER does so in five minutes, with the help of sophisticated server technologies that gather data from a multitude of sources. Funded by NASA’s Applied Science Program, RECOVER provides these data on specific fires to help fire managers to start rehabilitation plans earlier and implement recovery efforts quickly.
The researchers used the data layer showing historical fires since 1950, which were compiled from comprehensive databases by the U.S. Geological Survey Geospatial Multi-Agency Coordination, National Interagency Fire Center, Bureau of Land Management, U.S. Forest Service, and various state agencies such as the California Department of Forestry and Fire Protection. The historical fires do not include prescribed fires and undocumented fires. Learn more about the RECOVER program and its recent involvement with the Woosley Fire.
Has the Dept of the Interior been informed of these alarming facts and conclusions? If so, is there any attempt to develop a long range strategy to cope this imminent threat?
Fascinating work. I’m curious as to how the spatial and temporal elements of this work might correlate to population density and indirectly, the amount of electric power lines that have been installed in the urban/wildland interface areas throughout the Western US. Also, I would be curious to know if there is any relationship between forest land management practices on public lands in the West (as has been speculated in the media) and the occurrence of mega-fires in the West during this same period?
Nice study pulling together data from lots of sources and then documenting the changing Trend in fire activity. Thank you, NASA, for putting this out to the public.
One question – in the map under Point number 3, there seems to be no differentiation between BLM and private lands, both show as “clear.” Am I reading this map correctly?
Hi. Excellent analysis and publication.
In section 4, I didn’t understood this: “About 3 percent—almost a third of the land—”. Is that correct?
3% of the 11% mentioned, which is almost 1/3.
Hi. Excellent analysis and publication.
In section 4, I didn’t understood this: “About 3 percent—almost a third of the land—”. Is that correct?
Does the data analysis program assume climate change as the only possible control, as this article seems to suggest? Usually scientists develop multiple working hypotheses and test among them for validity. Are there other possible reasons for increased fires, such as changes in forest management practices over recent decades? Or increased intersection of areas with electrical installations (which seem to start many fires) with susceptible forests? You could test e.g. for a temperature control by looking for a spike in fires in the 1930’s, when temperatures were also high. Would like to know what a more rigorous analysis would conclude.
I am a retired wildland firefighter. Other factors that should be noted include the spread of invasive plant species in range areas..ie. Bromus Techtorum. The change in fire frequency at higher elevations and latitudes. The occurrence of wind events and dryness in certain areas. Human population dynamics as they relate to the Wildland Urban Interface. Cultural attitudes and understanding of fire in fire prone areas.
I did not see any reference to human population or habitation. I suspect that increases in human population and their choices of living locations has significantly affected the number of fire starts.
Why did the NASA choose 1950 as the starting point for the charts of fire frequency and size? If they had chosen 1900, the charts would have looked very different: fire frequency and size were highly variable in the early 1900s and probably before, with many years far surpassing current fire frequency and size maximums. The “lull” between the 1930s and 2000 indicate that fire-suppression was very successful, and perhaps that we were in a relatively wet, mild period.
I enjoyed reviewing this comprehensive analysis which will help understand the environmental factors that influence the incidence, severity, and damage from the wildfires during the last few years. The most recent devastating wildfires in California, the Camp Fire and the Woolsey Fire, affected entirely different types of terrain and vegetation. Was the pattern of these fires consistent with other California wildfires in the last 10 years?
There have been and are attempts within some former wildfire zones to restore native plant vegetation. Are there studies which can assess the impact of these ecologically restored areas?
Elaine M. George
I enjoyed reviewing this comprehensive analysis which will help understand the environmental factors that influence the incidence, severity, and damage from the wildfires during the last few years. The most recent devastating wildfires in California, the Camp Fire and the Woolsey Fire, affected entirely different types of terrain and vegetation. Was the pattern of these fires consistent with other California wildfires in the last 10 years?
There have been and are attempts within some former wildfire zones to restore native plant vegetation. Are there studies which can assess the impact of these ecologically restored areas?
A lot of people die each year due to fire accidents so it is very important to aware people about maintaining electrical & fire safety at home or workplace.
hudsonelectricalnb.com.au