California is due for a mega-flood that could force 1.5 million people to evacuate and cause $725 billion in damage - and it would hit Silicon Valley hard

Getty ImagesPeople look at cars and homes engulfed in floodwaters on February 22, 2017 in San Jose, California.

• A report from the US Geological Survey and a new book from Lucy Jones, an esteemed seismologist, say that an extreme storm could hit California.
• Dubbed ARkStorm, the disaster would overwhelm flood-control systems, force 1.5 million people to evacuate, inundate 25% of California's land, and cause $725 billion in damage. The storm's flooding would devastate much of the state, from Silicon Valley to Los Angeles.
• California's current flood-protection systems are not designed to handle an ARkStorm, according to Jones and other experts.

In California, earthquakes are common, and most residents understand the risks of powerful reverberations destroying their homes and streets.

But according to a new book from LA's most famous seismologist, Lucy Jones, the state faces an even bigger threat: a megaflood that would pummel inland California.

Jones' book, "The Big Ones: How Natural Disasters Have Shaped Us (and What We Can Do about Them," looks at the history of the world's biggest earthquakes, floods, tsunamis, hurricanes, and volcanic eruptions - as well as disasters we could experience in coming years.

One nightmare scenario investigated by the US Geological Survey, dubbed ARkStorm, would bring a series of heavy rains in a short timespan to California. The state could suffer extreme rainfall that overwhelms flood-control systems, forces 1.5 million people to evacuate, inundates 25% of California's land, and causes $725 billion in damage.

Bringing as much as 15 times the water flowing out of the Mississippi River's mouth, an ARkStorm could devastate several areas in California, including Silicon Valley.

According to Jones and the USGS, a major flood like this could strike in any future winter. California has also seen an ARkStorm before.

California has a history of monster storms

Eighty years ago, during one of the driest March-through-February periods ever recorded in the region, an epic series of storms caused mudflows that damaged and destroyed hundreds of homes in Southern California. As The Los Angeles Times notes, rain fell as fast as two inches an hour, inundating railroads, bridges, and roads throughout the San Fernando Valley. At least 21 people died.

Nearly a century earlier, the Great Flood of 1862 submerged most of the Central Valley and Los Angeles Basin. Every major city in the region flooded, and downtown Sacramento was only accessible by boat. One-third of California's taxable land was destroyed, rendering the state bankrupt. The flood also killed just over 1% of the state's population.

These two storms produced precipitation that exceeded levels that many places in the US experience once every 500 to 1,000 years on average.

They did serve as wake-up calls for California, however. Local officials responded by building dams and making rivers deeper to mitigate future flooding following the 1938 flood. And after the Great Flood of 1862, California temporarily moved its capital to San Francisco.

But Jones writes that California's modern-day flood-control systems aren't equipped to handle another storm of that magnitude.

How to make California more resilient to mass floods

In the last chapter of Jones' book, she lays out ways that California cities can prepare for the next big storm.

For example, LA could invest more heavily in solar energy or rechargeable groundwater basins, which would both help the city mitigate climate change in the longterm and reduce reliance on power lines and old aqueducts during a storm in the meantime.

Another resource for LA residents is the Community Emergency Response Training program, which allows neighborhoods to design their disaster response block-by-block.

California is not equipped to handle mass flooding

California's flood-control systems need massive overhauls, according to the USGS. Its existing levees aren't designed to withstand an ARkStorm, which could cause a flood 300 miles long and 20 or more miles wide.

The agency's report also includes terrifying maps of hypothetical flooding that would happen during an ARkStorm. As seen below, it would plunge much of Sacramento, Northern Orange County, and Stockton underwater.

USGSHypothetical flooding in an ARkStorm event in Sacramento.

USGSHypothetical flooding in an ARkStorm event in Stockton.

Other California cities that could see extreme flooding in coming years include areas in and around Silicon Valley (Among them: Santa Clara, Mountain View, Cupertino, San Jose, Palo Alto, Menlo Park, Foster City, San Mateo, Burlingame, Fremont, and Newark).

State and local agencies allocate $30 million annually toward maintaining 1,600 miles of levees in the Central Valley. But Michael Mierzwa, the lead flood management planner for the California Department of Water Resources, told The LA Times they should be spending $130 million per year to meet current federal standards.

Just last year, the Lake Oroville Dam north of Sacramento buckled after a series of torrential winter storms. The structure crumbled on one side, spilling a massive amount of water onto the dam's walls. If the state hadn't unplugged the dam in time, its walls would've likely eroded and unleashed all that water onto the surrounding communities.

"California flood protection is not designed for an ARkStorm-like event," the USGS writes.

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