Color-coded radar maps reveal a patchwork of devastation from wildfires

Color-coded radar maps reveal a patchwork of devastation from wildfires

Every year in California, thousands of wildfires consume hundreds of thousands of hectares of land. Deciphering how large swaths of vegetation have recovered over time can be difficult from the ground. New radar maps now reveal a patchwork of vegetation destruction and regrowth in the wake of more than a decade of fires in the Angeles National Forest and other areas near Los Angeles.

A NASA research aircraft equipped with radar instruments, known as UAVSAR, flew over Southern California several times from 2010 to 2020 to produce the detailed map of the terrain below. By sending microwave pulses toward the Earth's surface and measuring the signals that bounce back, the devices can detect changes of a few millimeters in surface elevation. They're also sensitive to humidity, says Yunling Lu, a radar engineer at NASA's Jet Propulsion Laboratory in Pasadena, California. The resulting maps can distinguish areas with trees and shrubs similar to bare ground.

Lu and her colleagues are developing an approach to color-code maps by year to track large-scale changes in vegetation and monitor the recovery of forests and shrubs after devastating wildfires. Areas with vegetation are shown in red in 2010, green in 2017, and blue in 2020. When the three maps are layered on top of each other, they tell a story of loss and regrowth. For example, the 2016 Fish Fire destroyed vegetation that was there in 2010 and did not grow back by 2017 or 2020, so it still appears red in the composite map. The area affected by the 2020 Bobcat Fire is shown in yellow: vegetation was present in 2010 and 2017 (red and green combine to produce yellow) but not in 2020.

The multi-color approach combines vegetation maps from 2010 (red), 2017 (green), and 2020 (blue). A closer look at the Angeles National Forest and other areas near Los Angeles shows how certain fires over the past decade have shaped forests and shrubs. For example, the area affected by the 2020 Bobcat Fire is yellow because vegetation was present in 2010 and 2017 (red and green combine to produce yellow) but not in 2020.Joshua Stevens/NASA Earth Observatory
Map of changes in vegetation near Los Angeles in 2010, 2017 and 2020
The multi-color approach combines vegetation maps from 2010 (red), 2017 (green), and 2020 (blue). A closer look at the Angeles National Forest and other areas near Los Angeles shows how certain fires over the past decade have shaped forests and shrubs. For example, the area affected by the 2020 Bobcat Fire is yellow because vegetation was present in 2010 and 2017 (red and green combine to produce yellow) but not in 2020.Joshua Stevens/NASA Earth Observatory

“Much of the Angeles National Forest has been affected by fire at some point, and you have patches that are in different stages of regeneration,” says Nayara Pinto, a landscape ecologist at JPL. The color-coding method can allow researchers to identify factors, such as vegetation and soil types, that influence why distinct areas regenerate at different speeds. It is also possible to use such maps to identify burned areas without vegetation that are at risk of landslides.

The team continues to develop additional ways to use the data collected by UAVSAR. The radar can also penetrate smoke or clouds, allowing it to track wildfires in real time to help firefighters fight fires effectively.

Jack J Lee

Jack J. Lee is a freelance science writer based in the San Francisco Bay Area. He holds a bachelor's degree in biology and a doctorate degree. in Molecular Biology, and recently completed a Master's program in Science Communication.

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