New Study: Mega-Floods Could Make Central Valley a ‘Vast Inland Sea’

Scientists are warning that the simmering climate may bring monster storms, unleashing Biblical torrents upon the state of California

Adding to the destructive forces of wildfires, droughts, and earthquakes that have long wreaked havoc upon California, climate change has doubled the likelihood of a megaflood unleashing absolute chaos upon the central valley.

California has had mega-floods before—the Great Flood of 1862 is one notable example—but according to a new study, we’ll be seeing them more often and with more fury as the climate continues to warm.

Scientists Daniel Swain of UCLA and Xingying Huang of the National Center for Atmospheric Research in Boulder, Colorado, published their findings in ScienceAdvances on Friday, the New York Times reports. The study claims that as the planet continues to warm, events that were once seen every 100-200 years, could be seen three times a century.

If a mega-flood such as the 1862 disaster were to strike today it would devastate California’s industries and displace millions of citizens, according to the authors.

“California has vastly expanded its rural, urban, and agricultural sprawl, which could lead to more potential for loss of life and property.” Alan Rhoades, a hydroclimate research scientist at Lawrence Berkeley National Labratory told the Washington Post. The financial cost of such a catastrophe could run well over $1 trillion dollars.

The study uses a 2010 worst case scenario simulation—ARkStorm—and developed ARkStorm 2.0, broadening their data sample by drawing “upon a much wider range of physically plausible event sequences.” The team also used “a newer and more sophisticated weather model” which designed and implemented two separate scenarios: ARkHist and ARkFuture. The two scenarios compare a “present era severe storm sequence [ARkHist] to a much more intense but physically plausible future sequence amplified by climate change [ARkFuture].”

“Atmospheric rivers”—essentially airborne pipelines of water vapor—would hit California during wet years with massive amounts of water over extended periods. Although California is in desperate need of precious H2O, these events could lead to extreme runoff, overwhelming dams across the state and causing mass flooding.

The researchers predict that so many dams failing at once would essentially inundate the Sacramento and San Joaquin valleys, creating a “temporary but vast inland sea.”

And it’ll only get worse as the climate continues warm. By 2060, the likelihood of an ARkHist event increases by 374 percent.

“We find that the annual likelihood of an ARkHist level event increases rapidly for each 1°C of global warming,” the study says.

Every winter, to varying degrees, the Sierra Nevada range is blanketed with a layer of snow. As the climate warms, however, the snow line will begin to creep upward, causing less water to gather in the snowpack, fundamentally altering “mountain hydrology and subsequent watershed response.” If one of these ARkFuture storms were to happen, the study found it could produce up to 400 percent higher runoff. When considering the implications this could have on recent burn areas, the potentially ensuing debris-filled flash floods could be unprecedented.

In regards to a future storm event, Swain said in a press release that “there are localized spots that get over 100 liquid-equivalent inches of water in the month. On 10,000-foot peaks, which are still somewhat below freezing even with warming, you get 20-foot-plus snow accumulations. But once you get down to South Lake Tahoe level and lower in elevation, it’s all rain. There would be much more runoff.”

California’s environmental forces certainly seem to be producing a lot of doom and gloom, but the study mentions a couple ways to mitigate the destruction—and even provides a solution that could work in our favor. The ability to forecast such storms would allow reservoir operators to make more informed decisions, and floodplain restoration and levee setbacks would “lessen flood risk in urban areas.”

The study also states that interventions like “Flood-Managed Aquifer Recharge,” or the injecting of floodwaters into aquifers, could even improve “resilience to future regional droughts.”

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