Disastrous megaflood could sink much of Bay Area underwater in 30 to 40 years, experts say

ByDavid Louie KGO logo

Tuesday, August 16, 2022

Megaflood could sink much of Bay Area under water, experts say

As a result of climate change, scientists say mega storms will put much of the Bay Area and Northern California under water in the next 30-40 years.

SAN FRANCISCO (KGO) -- The next climate crisis across the Bay Area and virtually much of Northern California could be megafloods: Major storms lasting for weeks that will put many bayshore cities and critical infrastructure underwater.

The drought and wildfires are alarming. However, climate scientists say we should be planning ahead.

"We were kind of blindsided by the increase in extreme wildfire," said UCLA's Daniel Swain Ph.D. "And there's a desire to not be blindsided by the increase and risk of extreme floods." Swain briefed reporters, meteorologists and other climate experts Monday for over an hour on Twitter Spaces.

Residents in low-lying cities along the bayshore, San Francisco and Oakland airports, and freeways would be flooded as mega storms dump rain for three to four weeks, not days, as a result of climate change.

Swain warned, "Think the highest king tides you've ever seen and then add a foot or two on top of that, and then add an additional increment of flooding risk coming from all the water that would be rushing down from the hills and the rainfall in the coastal mountains, so you'd see a significant amount of flooding along the bayshore."

Swain warns of the risk in a study he co-authored at UCLA's Institute of the Environment and Sustainability. Flood risk, he points out, increases when wildfires burn ground cover, causing storm runoff to overwhelm rivers and streams. Mudslides and debris also reduce waterway capacity. We saw what that can do in San Jose along Coyote Creek five years ago.

VIDEO: Atmospheric river pummels Bay Area with heavy rain, strong winds

Highway 92 towards Half Moon Bay flooded and crews spent Monday evening unclogging drains along Highway 82 in Burlingame, San Mateo, and Hillsborough.

Climate scientists now are trying to get local, state and federal agencies to start planning for these megafloods.

"We can't tell you exactly when," he said, "but there may be a decade at some point in the next 30 or 40 years where we have a surge in severe floods just like we saw with severe wildfires."

Swain could not project the potential cost of preparing or preventing megafloods. He said that will be included in future studies.