California has made a lot of progress in earthquake preparedness in recent decades, but Brett Sanders isn’t sure Los Angeles is ready for “the Big One” when it comes to flooding.

Sanders and his team at the UCI Flood Lab built a comprehensive model to determine the flood risks for Los Angeles in the event of a one percent annual chance flood (formerly referred to as a 100-year flood) and found that, depending on how big the flow was, between 100,000 to 600,000 people would be affected; this is 10 to 40 times larger than estimates provided by FEMA maps, which suggest approximately 20,000 residents would be affected. Sanders pointed out that this discrepancy “was at least an order of magnitude greater.”

“We never plan for those events that are bigger than what our infrastructure was designed for,” said Sanders. “And now, as the atmosphere is getting warmer, as more and more land is converted from forests and soft surfaces into harder surfaces, there’s more runoff, there’s more people living in hazardous areas, and we don’t plan for that.” And to make matters worse, there’s a fundamental misunderstanding of flood risk. Most people don’t realize that infrastructure is not built to withstand extreme flooding.

This is especially an issue for renters because “all of our thinking about flooding is tied into homeownership,” explained Sanders. Much of the mapping in the U.S. has been to support the National Flood Insurance Program, which offers subsidized insurance to property owners. Homeowners are required to sign an acknowledgment when buying property in a flood zone, and mortgages require flood insurance, but renters are usually unaware of the risks in their area.

“It’s confusing for the average person to navigate,” said Sanders. “That’s where we want good government to play a role so that the average person can go to work and earn a paycheck and feed the family and all those things.”

Sanders and his team met with the public works organizations of Los Angeles and Orange County during the early stages of their study. After it was published, the Los Angeles Board of Supervisors passed a motion to look into these flood risks and inequities.

But will it happen in time? “It’s one of those problems that you don’t see change happening very fast, and it ought to be because we’re seeing more and more severe floods,” said Sanders.

Flood risks are rising with climate change. However, investments in infrastructure and solutions like river restoration can help keep more Angelenos safe and dry. According to Sanders, “It’s a growing problem, but it’s one that we can do something about.”