Sunday and Monday marked the third wettest two-day period on record in Los Angeles, according to meteorologist Ariel Cohen during a press conference today. Some parts of the city have seen more than a foot of rain, and all that water has brought power outages, fallen trees, flooding, and hundreds of mudslides, especially in the canyons.
“In California, our atmospheric river storms are comparable to hurricanes in the amount of rain that they bring, and therefore the damage that they can do,” says Lucy Jones, seismologist and author of The Big Ones: How Natural Disasters Have Shaped Us (and What We Can Do About Them). “But because we don't name them, and the wind is somewhat separate from the rain, we often underestimate what they're going to be.”
She says the damage could’ve been worse if winds were stronger, but storm duration also matters.
“One definition of really intense rain is 16 inches in a three-day period. … But there's only so much damage you do in just three days. Imagine if it kept on going.”
Jones and her colleagues did imagine such a disastrous scenario using real historical storm data. “Back a decade ago … we made the ARkStorm model for these atmospheric river storms, ARk being atmospheric river 1000.” (The number 1000 refers to the 1 in 1000 chance of such a storm happening in a given year in any one location.)
She points out that in 1861-1862, rain fell for 45 days straight in California, totalling 50 inches and killing 1% of the state’s population — making it the biggest disaster in state history. It wiped away mining communities in the Sierras and the town of Agua Mansa, which was on the banks of the Santa Ana River and the largest town between LA and New Mexico.
The likelihood of another such storm occurring is higher now on account of climate change, Jones says, so storm infrastructure must be improved. But she points out there will always be a storm that’s stronger than what flood control systems can withstand.
Jones is most concerned about levee systems typically found in northern parts of the state, which are largely built by farmers for agricultural purposes. If the levees fail, “we can have way more damage than what we've got now,” she explains.
The same goes for stormwater channels. “The LA River hasn't flooded since it was channelized in 1938,” Jones notes. “[But] there will be a storm, at some point, that will exceed it, almost by definition.”
So does seismologist Jones fear intense storms more than a big earthquake? According to her ARkStorm models, “the Big Storm” is likely to cause $800 billion in damage to the state, four times as much as “the Big Earthquake.” That’s in part because megastorms can affect the entire state, not just individual areas.
But, Jones says, storms are more predictable than earthquakes, which gives us more of an opportunity to prepare and get folks to safety. “If you handle [storms] right, if you do your evacuations right, you don't kill people,” Jones says. “We don't have that option with earthquakes. All of that has to be done with preparation and building better buildings.”
The key will be convincing people that preparing for the “Big One” also means being ready for floods, not just earthquakes. “Psychologically, we do not fear rain as much as we do earthquakes, even though they kill as many, if not more people.”