Predicting Post-Fire Debris Flows from Space
Portland, Ore., USA: Over the past few years, wildfires have ripped through
forests around the world with no signs of slowing down. The devastation of
a wildfire can be severe on its own, but there are additional hazards to
consider after the flames have been extinguished.
Debris flows are fast-moving slurries of soil, rock, and water that can
seemingly form out of nowhere. They race down slopes, carrying and
engulfing anything in their path. Bare, fire-ravaged slopes are a perfect
setting for the development of these hazardous flows.
“The biggest issue is any sort of steep area where you can essentially
bring large quantities of sediment down slope,” says Eli Orland, an
associate scientist at the Universities Space Research Association (USRA)
in NASA Goddard Space Flight Center’s Hydrological Sciences Laboratory.
Orland is a coauthor of a new study to be
on Tuesday at the Geological Society of America’s annual meeting. “In this
case, gravity is not exactly your friend,” he adds.
In the U.S., post-wildfire debris flow hazards are modeled and monitored by
the U.S. Geological Survey (USGS) and affiliate organizations like the U.S.
Forest Service (USFS) Burn Area Emergency Response Team (
). These scientists address conditions on the ground after a fire to
identify areas that may be prone to additional damage from
flooding—including debris flows.
“[The USGS] and USFS are the foremost organizations in the United States
for post-wildfire hazard response,” says Orland. Scientists and emergency
responders look to rapidly identify areas of concern for post-fire impacts,
but these site surveys and field-based data collection are time consuming.
Orland points out that there are many areas around the world that do not
have the resources or capability to quickly assess post-wildfire
conditions. The NASA team wanted to develop new information that these
communities may use to change that.
The researchers are aiming to see if remote sensing data could be used
identify areas of debris flow hazards in regions experiencing wildfires—all
without setting boots on unstable ground. The team created a model to
assess post-fire debris hazards, using freely available data that captured
rainfall intensities, burn severity, and topography.
Precipitation data was collected from NASA’s Global Precipitation
Measurement (GPM) mission, which incorporates infrared and passive
microwave data from several satellites to provide measurements of
precipitation intensity around the globe, every half hour—a process that
Orland says occurs “in near real-time.” Burn severity was determined by
satellite imagery from the Landsat (NASA/USGS) and Sentinel (European Space
Agency) programs, and steep slopes are identified from digital elevation
model data from NASA’s Shuttle Radar Topography Mission.
Using this satellite data, the team creates a model that identifies areas
at high risk of debris flows after a fire. They rely on the detailed,
ground-based data collected by USGS to further refine and train their
model, using machine learning technologies.
“There are so many different ways that artificial intelligence and machine
learning are used today to understand and approximate hydrologic processes
and hazards,” said Dalia Kirschbaum, chief of the Hydrological Sciences
Laboratory at NASA Goddard and a co-author of the study. “One of the things
that’s actually quite limited in post-fire debris flow work is the
availability of event inventories on a global scale that allow us to
establish these relationships,” she explained, adding that it was critical
to use the information collected by the USGS, USFS, and their partners for
When they tested their model against data from several burned areas
surveyed by USGS to identify the potential for post-fire debris flows, they
found that short-duration, high-intensity rainfall in the GPM record is
most frequently the trigger for debris flows—an observation consistent with
previous research, but the first evidence that these relationships are
discernable from satellite-derived global precipitation data. “The
satellite data really shows promise in being able to resolve the post-fire
debris flow hazards at a larger watershed level,” she notes.
Kirschbaum says that their work currently provides a big picture overview
of hazards for a region. She hopes that in future models, the team can
tease out details about not only where debris flows originate, but where
they might flow—an important factor in hazard mitigation.
The researchers note that work shouldn’t replace detailed, ground-based
investigations. Kirschbaum says their goal is to provide near–real-time
information and tools for emergency responders around the world to better
prepare for potential hazards after a wildfire.
Universities Space Research Association, NASA Goddard Space Flight Center,
Paper No. 148-6:
Real-Time Assessment of Post-Fire Debris Flow Hazards Using Globally
Tuesday, 12 Oct., 9:50 a.m. PDT
Session 148: T134. Advances in Wildfire-Related Earth-Surface Processes I:
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