Although drought and wildfires have been the predominant feature of weather in California recently, the state could be facing a much bigger weather disaster in the form of massive rainfall and flooding.
The New York Times takes a look at what they call a megastorm, a gigantic flood caused by a series of atmospheric rivers dumping unprecedented amounts of rain on the state. This has happened in the past and it will happen again in the future. But California is now home to almost 40 million people and the economic impact will be greater than the much hyped "Big One" earthquake.
The coming superstorm — really, a rapid procession of what scientists call atmospheric rivers — will be the ultimate test of the dams, levees and bypasses California has built to impound nature’s might.
But in a state where scarcity of water has long been the central fact of existence, global warming is not only worsening droughts and wildfires. Because warmer air can hold more moisture, atmospheric rivers can carry bigger cargoes of precipitation. The infrastructure design standards, hazard maps and disaster response plans that protected California from flooding in the past might soon be out of date.
As humans burn fossil fuels and heat up the planet, we have already increased the chances each year that California will experience a monthlong, statewide megastorm of this severity to roughly 1 in 50, according to a new study published Friday. (The hypothetical storm visualized here is based on computer modeling from this study.)
In the coming decades, if global average temperatures climb by another 1.8 degrees Fahrenheit, or 1 degree Celsius — and current trends suggest they might — then the likelihood of such storms will go up further, to nearly 1 in 30.
At the same time, the risk of megastorms that are rarer but even stronger, with much fiercer downpours, will rise as well.
If you think the NYT article is scaremongering, read this article from Scientific American. It describes what happened in California over the winter of 1861-1862.
Sixty-six inches of rain fell in Los Angeles that year, more than four times the normal annual amount, causing rivers to surge over their banks, spreading muddy water for miles across the arid landscape. Large brown lakes formed on the normally dry plains between Los Angeles and the Pacific Ocean, even covering vast areas of the Mojave Desert. In and around Anaheim, , flooding of the Santa Ana River created an inland sea four feet deep, stretching up to four miles from the river and lasting four weeks.
Residents in northern California, where most of the state’s 500,000 people lived, were contending with devastation and suffering of their own. In early December, the Sierra Nevada experienced a series of cold arctic storms that dumped 10 to 15 feet of snow, and these were soon followed by warm atmospheric rivers storms. The series of warm storms swelled the rivers in the Sierra Nevada range so that they became raging torrents, sweeping away entire communities and mining settlements in the foothills—California’s famous “Gold Country.” A January 15, 1862, report from the Nelson Point Correspondence described the scene: “On Friday last, we were visited by the most destructive and devastating flood that has ever been the lot of ‘white’ men to see in this part of the country. Feather River reached the height of 9 feet more than was ever known by the ‘oldest inhabitant,’ carrying away bridges, camps, stores, saloon, restaurant, and much real-estate.” Drowning deaths occurred every day on the Feather, Yuba and American rivers. In one tragic account, an entire settlement of Chinese miners was drowned by floods on the Yuba River.
This enormous pulse of water from the rain flowed down the slopes and across the landscape, overwhelming streams and rivers, creating a huge inland sea in California’s enormous Central Valley—a region at least 300 miles long and 20 miles wide. Water covered farmlands and towns, drowning people, horses and cattle, and washing away houses, buildings, barns, fences and bridges. The water reached depths up to 30 feet, completely submerging telegraph poles that had just been installed between San Francisco and New York, causing transportation and communications to completely break down over much of the state for a month.
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