New analysis from NASA shows that major flooding in cities along the West Coast could become a serious problem if a strong El Niño develops this winter, which is widely expected.

NASA’s sea level change science team analyzed data and determined that an increase in high-tide flooding could swamp roads and spill into low-lying buildings if the periodic climate phenomenon has a prolonged stay in the western U.S.

El Niño happens every few years and is characterized by sea levels that are higher than normal and above average temperatures in the Pacific along the equator.

This year, a particularly strong El Niño could result in “ten-year flood events” in major cities, including Seattle and San Diego, NASA warns. In South America, Ecuador could see up to three of these same flood events.

Even more alarming than the risk of devastating floods this year, scientists caution that these natural disasters could soon become commonplace.

Currently, these historic flood events are unlikely to happen during non-El Niño years, NASA says, but that could change by the 2030s due to rising sea levels and climate change. These cities could experience these 10-year floods annually, with or without El Niño NASA says.

“I’m a little surprised that the analysis found these 10-year events could become commonplace so quickly,” said Phil Thompson, an oceanographer at the University of Hawaii and a member of NASA’s sea level change science team. “I would have thought maybe by the 2040s or 2050s.”

A ten-year flood is an event that has a 1 in 10 chance of occurring in any given year and is a measure of how high local sea levels can rise.

“Ten-year floods can result in what the National Oceanic and Atmospheric Administration classifies as moderate flooding, with some inundation of roads and buildings, and the possible need to evacuate people or move belongings to higher ground,” NASA said.

NASA says the extent of flooding in specific cities depends on multiple factors, including a region’s terrain and the location of homes and infrastructure near the ocean.

Because water expands as it warms, sea levels tend to be higher in places with warmer water. Sea levels are rising due to the overall warming of the planet due to the heating of the earth’s atmosphere and the melting of ice sheets and shelves.

These rising temperatures have already increased the total number of high-tide flooding days that cities along the coast experience every year. Those flooding risks are compounded by storm surges and weather events like El Niño.

“As climate change accelerates, some cities will see flooding five to 10 times more often,” said Nadya Vinogradova Shiffer, of NASA’s Surface Water and Ocean Topography mission. “SWOT will keep watch on these changes to ensure coastal communities are not caught off guard.”

NASA monitors sea levels through various missions and initiatives in hopes of collecting enough data to help legislators and local leaders prepare their communities for rising sea levels, which are almost assured to continue to be a problem in the coming decades.

To read more about NASA’s sea level monitoring studies, click here.