NASA's SWOT Satellite Exposes Big Gaps in Outburst Flood Models

When Ukraine's Kakhovka Dam was destroyed on June 6, 2023, the flood forced thousands to evacuate as water levels rose 10 feet (3 meters) above normal. Such dam-break, or outburst, floods are notoriously hard to study because by the time researchers can safely reach a site, only the aftermath remains. But a NASA satellite happened to be collecting measurements over the region when the dam failed, giving scientists a rare real-time view of the flood.

Researchers at Georgia Tech used those observations, from NASA's Surface Water and Ocean Topography (SWOT) satellite, to test how well existing outburst-flood models reproduced the actual event, and found the models consistently underestimated flood conditions. Even after improving the models with more realistic estimates of the reservoir and river-bottom topography, the team could not accurately capture both the height and timing of the floodwaters at once, according to the study, published in the journal Geophysical Research Letters.

SWOT uses two antennas and a technique called interferometry to measure water elevation with about 10-centimeter accuracy across rivers, lakes, wetlands, reservoirs and oceans, and it passed over the Kakhovka flood zone repeatedly, producing detailed daily measurements across the floodplain. "SWOT doesn't observe every flood that happens, but when it does, it provides exactly the information we've needed to understand how floodwaters move across the landscape," said Tamlin Pavelsky, a professor at the University of North Carolina at Chapel Hill and one of the study's authors.

"It's really challenging to collect real-world data from these huge floods because they're so localized, unpredictable and energetic," said Karin Lehnigk, a Georgia Tech postdoctoral fellow and the study's lead author. Because SWOT produced a new image daily covering the entire flood path, the team could compare models with real-world conditions across many locations and times in ways previously possible only in a lab. The results point to broader challenges in simulating large outburst floods, as aging infrastructure and extreme weather increase flood risks worldwide.