Like Texas, California faces major dangers when extreme floods come

Yahoo

08-07-2025

The deadly flash flood along Texas' Guadalupe River showed the devastating toll such a disaster can take, and California could face similar dangers when extreme weather strikes.
Low-lying areas along rivers and creeks can be hazardous when downpours and torrents come, as shown by past floods in parts of the state including the Los Angeles area, the Central Valley and the Central Coast.
When a series of extreme winter storms hit California in 2023, about two dozen people died statewide, including some who were swept away by floodwaters and others who were killed by a rock slide, falling trees or car crashes.
'Those risks exist here,' said Brett Sanders, a UC Irvine professor whose research focuses on flooding. 'We have a lot of the same possibility of flash flooding. We have hilly topography. We have streams that can spread out and catch you by surprise with water.'
California's history is dotted with examples of storms triggering dangerous inundations, such as 1861-62 floods that left Sacramento underwater, the deadly Los Angeles flood of 1934, and devastating debris flows following intense rains that struck the Santa Barbara County town of Montecito in 2018.
The flash floods in Texas left more than 100 people dead and others missing, among them children and counselors who were at a summer camp when floodwaters swept through the area. Officials described it as a '100-year-flood.'
Sanders said as he has looked at factors that contributed to the high death toll, he examined maps of federal hazard zones produced by the Federal Emergency Management Agency. He said, judging from the maps, it appears that a number of cabins at the summer camp were within a federally designated 'floodway' and were at high risk.
'Floodways are areas where you know the water will be moving really fast, and so you know that's going to be a really dangerous place to be,' Sanders said.
'There were people in harm's way that didn't know they were in harm's way,' he said. "There was a breakdown somewhere along the way, in the understanding of risks and the ability to take action in a timely way.'
Read more: Texas flood highlights deadly climate risk from extreme weather
There are many buildings in flood-hazard zones in California, he said, but it's rare to have buildings permitted in floodways here.
'It seems like much more could have been done to increase awareness about the risks of sleeping overnight next to a stream that's prone to flooding, and especially at a time when rainfall was forecast,' Sanders said of the Texas flood.
Daniel Swain, a climate scientist with UC Agriculture and Natural Resources, said the types of storms that tend to unleash floods in California are typically different from the intense thunderstorms that triggered the flooding in Texas.
'But the level of flooding and the suddenness and catastrophic impacts of it could very well be replicated in California,' Swain said during a media briefing. 'It would be more likely to occur with a sequence of winter storms, a particularly intense atmospheric river.'
He said such storms, which roll in from the Pacific Ocean carrying massive amounts of water vapor, would typically be on a larger scale.
'So it wouldn't just be affecting one section of one particularly vulnerable watershed, but would probably affect many watersheds simultaneously, which is part of why it's so concerning,' Swain said. 'But it would also probably be a little more predictable.'
There can also be cases, Swain said, in which a thunderstorm is embedded within a major winter storm. For example, he said, the extreme storm that produced the Montecito debris flow in 2018 came as a localized downpour in the mountains that was as intense as the deluge in Texas, though not sustained for as long.
The difference in Montecito, he noted, was that the rains loosened hillsides that had been charred by the Thomas fire.
'Similar idea: very localized, very extreme convective downpour that just completely overwhelms and is an almost unimaginable amount of water in a cloud burst,' Swain said.
Scientific projections indicate that risks of extreme floods are increasing in California and elsewhere because of human-caused climate change. Storms are able to dump more rain because warmer air can hold more water vapor.
Read more: How California's storms are projected to become more extreme with climate change
One part of the state that faces significant flood risks is Los Angeles County. L.A. County Public Works spokesman Kerjon Lee said that the county has been investing in flood protection and stormwater capture efforts in recent years to increase the area's resilience to the effects of climate change.
'We're using climate projections to develop a robust flood-protection network so communities can survive flooding and other extreme weather events and recover as quickly as possible,' Lee said in an email. 'Los Angeles County Public Works is also working to educate the public about flood risk so residents can develop emergency plans and reduce their financial risk through the purchase of flood insurance.'
In a 2022 study, researchers, including UC Irvine's Sanders, estimated that up to 874,000 people and $108 billion in property could be affected by a 100-year flood in the Los Angeles Basin, revealing larger risks than previously estimated by federal emergency management officials.
The researchers found that Black and low-income communities, because they are disproportionately in low-lying areas, would be hit especially hard in such floods.
Sanders said although the team's analysis showed the area faces major flood risks, California has had stronger local planning processes that have restricted construction in floodways.
'California has a lot of the same hazards, but we do have different levels, I think, of regulation, which have probably affected what's potentially exposed by these storms,' Sanders said. 'I think that California has got a stronger planning and flood-management mechanism in place than Texas does, which limits that risk.'
The state does, however, have various flood-prone campgrounds along rivers and creeks, Sanders said. And there are many homeless people living along rivers and flood-control channels who are at risk during floods.
Some of the victims during recent floods have been motorists who tried to drive through fast-moving waters, Sanders noted. 'Any kind of low crossing that that oftentimes turns into a torrent of water, it may look like it's shallow and you [can] get your car through, but a lot of times, cars get swept off the road, and then people lose their life. So that's another risk Californians face.'
The loss of life in the Texas disaster, Sanders said, points to 'a lack of risk communication, lack of risk awareness.' He said the disaster shows the importance of coordination between federal, state and local governments as well as property owners in keeping people safe when extreme floods come.
This story originally appeared in Los Angeles Times.