Landsat archive fills in tundra fire gaps

The fire ecologist didn’t know much about remote sensing when he and some colleagues began noticing burned areas on the Arctic Slope, and they knew the areas weren’t listed in the Great Alaska Fire Database, which includes fires dating back to 1939.

If fire records missed the tundra fire they stumbled upon, have they missed others in the past? Does the increase in the number of fires recorded in recent years really indicate a trend, or is it just improved detection methods?

Their quest for answers is motivated by more than personal curiosity. Lacking other sources, researchers use the Alaska Fire Database to study the tundra — and, in some cases, the effects of climate change. So the more complete the record, the better their results.

Miller tried to find the burned areas on Google Earth without success, but eventually he and his colleagues (including several U.S. Geological Survey (USGS) scientists familiar with remote sensing) decided the best approach was to turn to the longest existing satellite record of Earth observations: Landsatwhose more than 50-year archive is maintained and continually added to by the U.S. Geological Survey’s Earth Resources Observation and Science (EROS) Center.

Miller conducted a thorough search of the Landsat archive and found some interesting results in the Brooks Range foothills region, a stretch of Alaskan tundra located north of the Brooks Range and south of the Beaufort Coastal Plain on Alaska’s northern coast.

• Miller discovered 57 previously unknown fires, accounting for 41% of the total 138 new fires in the region.
• The frequency of fires has increased significantly in recent years.
• Despite increasingly advanced detection technology, most unknown fires are recent, not historic.
• The locations and sizes of some known fires listed in the fire database are inaccurate.

Analysis ‘snowballs’

Wildfires in remote tundra areas have long been thought to be rare because of the colder climate and fewer witnesses. Fires there are rarely put out because people may be unaware, firefighting resources are being used elsewhere or there are no structures to protect. Many fires in the past were known only because airplanes passed nearby or observers tracking storms noted the general location and size of the fire.

Landsat satellite images are the best option for a more comprehensive record. Earth Explorera Landsat data access website hosted by the U.S. Geological Survey Earth Observing Satellite System (USGS EROS), and began looking for eight to 10 burned areas that he and his colleagues had noticed on the landscape.

“I found them,” Miller said. “But the thing is, once you start looking, you start finding all these fires. It’s like a snowball. I never planned to go out and look.” Write this paper Or doing analysis or something like that. It all happened so organically—scanning on Landsat and finding all these different fires.”

In late 2022, Miller began a systematic search of the Brooks Range foothills throughout the Landsat archive, which goes back to 1972. He was familiar with the EarthExplorer site because he individually combed through a total of 790 scenes—an average of 17 per year, with a maximum of 32 in one year. The search did not include seven years in the 1990s, when there were gaps in the data for high northern latitudes. The project also used some historical aerial photos obtained through EarthExplorer.

Burned areas must meet certain criteria to count as unrecorded fires, including being identified in at least two scenes.

The unrecorded fires Miller found ranged from one-tenth of an acre to 689 acres, for a total of about 4,163 acres, or 1 percent of all previously known fires on the Arctic Slope. But they still account for about two-fifths of all currently known fires.

Landsat also helped improve the accuracy of recorded fires. Passengers next to the pilot may have estimated coordinates and sizes, or called out locations based on vague landmarks. Miller found a more realistic picture from Landsat. Some of the burnt areas he found he thought were not recorded until he realized they were inaccurate.

“A lot of the old burn marks are pretty far apart,” Miller said.