A strong El Niño could mean a 10-year flood in Seattle this year, NASA says. What to know
An El Niño year typically means warmer and dryer weather for the Pacific Northwest, but new analysis from NASA’s Jet Propulsion Lab has found that may not be the case for the Puget Sound this winter.
In fact, it won’t just be rainy. NASA found that if a strong El Niño forms, as is expected, Seattle is at risk of being hit by a type of flooding called a 10-year flood - up to five times this winter.
A 10-year flood has a one-in-10 chance of happening in any given year, according to the United States Geological Survey. Weather experts also measure for 100-year and 500-year floods.
The National Oceanic and Atmospheric Administration classifies a ten-year flood as a storm that causes moderate flooding, some inundation of roadways and buildings, and the possibility of evacuations or needing to move belongings to higher ground. The last time Seattle area saw flooding of moderate level was in 2009. According to National Weather Service data, it flooded along the Cedar River in Renton, which is the NWS’s closest river marker to downtown Seattle.
Seattle wasn’t the only city that NASA highlighted as being in danger of a 10-year flood. San Diego, California, and La Libertad and Baltra in Ecuador, are also at risk of up to three 10-year floods this winter. The two Ecuadorian cities are over 4,200 miles south of Seattle.
Why do 10-year floods occur?
Based on previous weather patterns, 10-year floods typically occur along the western coast of the Americas during El Niño years.
El Niño occurs when trade winds — the permanent east-to-west winds that blow near the equator — weaken, allowing the Pacific Ocean’s warmer waters to push back east toward the United States west coast.
“When the ocean is warmer, that tends to make the weather in the inland areas of the Pacific Northwest a little warmer also,” Nicholas Bond, University of Washington researcher and state climatologist, previously told McClatchy News. “That air that is moving over warmer than normal water is just going to pick up a little bit of extra heat.”
When the sea-surface temperatures of a large part of the ocean are several degrees above average, it’s considered a marine heatwave. These conditions can lead to storms absorbing more energy and moisture from the atmosphere, similar to how a hurricane works, and bring stronger storms through coastal areas.
Will 10-year floods become more common in Washington?
NASA researchers fear that as climate change continues to affect the northeastern Pacific Ocean, 10-year floods could become more regular in the Puget Sound region.
According to NASA’s analysis, if sea levels continue to rise and warm, 10-year floods could be an annual occurrence for Washington state, even in non-El Niño years. During strong El Niño years, 10-year floods could occur up to 10 times annually by the 2030s and up to 40 times annually by the 2050s.
“I’m a little surprised that the analysis found these 10-year events could become commonplace so quickly,” Phil Thompson, an oceanographer at the University of Hawaii and a member of NASA’s sea level change science team, stated in the published analysis.
Rising sea levels are also a concern for other NASA scientists, too. The Jet Propulsion Lab has found that flooding days in coastal areas worldwide have increased as the oceans are heating up and ice sheets melt.
Nadya Vinogradova Shiffer, director of the ocean physics program at NASA Headquarters, said in the analysis that by the 2030s, some coastal communities could expect to see flooding five to 10 times more often than today.
This story was originally published November 9, 2023 at 1:23 PM.
