Of course, our present reality is such that historical conditions, and the risks and constraints associated with them, are becoming less and less relevant. In 2011, a team of more than 100 scientists, engineers and other experts convened by the U.S. Geological Survey modeled what a similar storm — they called it the ARkStorm, for Atmospheric River 1,000 — would do to the California of today, with its much larger population and expansive, vulnerable infrastructure. The answer included hundreds of landslides, millions of people evacuated and financial damages more than three times as high as what even a severe earthquake might bring. But that assessment looked only at the potential impacts of a storm of historic proportions. Climate change is not only making events like the 1862 catastrophe more likely to occur (by 300 to 400 percent, according to one estimate); it is also creating the conditions for storms that will make the 1862 flood look small. The two atmospheric rivers that led to a near catastrophe at Oroville, one study found, carried 11 to 15 percent more rain than would have been possible if humans had not altered the atmosphere. And the largest rivers of the future will be even bigger, last longer and carry water at a much higher density. They will also arrive more often.
When the climate scientists Xingying Huang and Daniel Swain modeled ARkStorms based on California’s predicted conditions, they found that future storms would be able to douse California with a load of water 45 percent greater than anything that has been possible under historical conditions. Because the precipitation is likely to fall quickly and be tilted toward rain instead of snow, peak runoff would mean between two and four times as much water racing across the landscape as during the largest floods of the past.
That updated analysis was published in August 2022, when California was once again parched: More than 99 percent of the state was officially in drought, and large swaths were considered extreme or exceptional. “The apparent irony of publishing research on the growing risk of a California megaflood in the midst of a severe drought is not lost on the authors,” Swain wrote on his blog. At the time, forecasts called for the dry trend to continue, but Swain cautioned that California should not make the old mistake of forgetting the wet times during the dry ones. The research suggested, he wrote, that “it’s only a matter of time before this latent increase in severe flood risk becomes ‘unmasked’ in the Golden State.”
The months that followed were no ARkStorm but quickly offered a startling reminder of how unprepared the state is even for smaller events. By the end of March, 31 atmospheric-river storms, including six classified as strong and one as extreme, hit the West Coast. Near Sacramento, the Cosumnes River broke out of its levees. Three people died, and an evacuation order had to be rescinded when floods made the roads too dangerous for escape. A creek outside Planada filled the town with waist-high water, destroying houses and cars. In the Bay Area, high winds shattered the glass of skyscrapers, blew a couch from a high-rise apartment onto the sidewalk below and killed five people in a single day. Tornadoes touched down outside Los Angeles, and snow fell as low as the Hollywood sign. In the San Bernardino Mountains, the snow drifts piled so high that roofs collapsed, natural-gas lines fractured and caused fires and the Sheriff’s Department had to airlift rations to people who were stranded. Water managers worried that the disaster some had started to call the Big Melt was just beginning.
Driving over the coastal mountains during one of this spring’s weaker atmospheric rivers, I had to pull over to wait out blinding rain and a fusillade of flying tree branches. I was on my way to visit Pajaro, a town south of Santa Cruz. Nearly two weeks earlier, the Pajaro River broke through a levee at midnight, prompting a hurried evacuation of 8,500 people, many of them workers in the valley’s berry and salad industries. Families were still sleeping in cars or in hotels or in the makeshift shelter at the county fairgrounds, their debts mounting while their homes sat empty and the fields were too flooded to be worked. Every day people gathered on the edge of the closed bridge leading to town, where the river still ran high and brown and tents dotted the riverside, to ask when they would be allowed to resume their lives. On the day they were permitted to re-enter town, nearly two weeks after the flood, I watched shopkeepers mucking out buildings and residents wheeling home bottles of donated water. The public water system was still inoperable.
Andrew Fisher, a professor at the University of California, Santa Cruz, who has studied the Pajaro River watershed since the 1990s, told me that he regards it as a microcosm of the problems and possibilities of California’s water future. For decades, it has been known that the levees on the river were dangerously out of date, designed for the more moderate California of the past. By the time of this year’s floods, the levees were prepared for only an eight-year flood, or one with about a 12 percent chance of happening in any given year — hardly the contingency that infrastructure should be built to address. “That’s kind of putting up a flimsy garden fence around your property to keep out wildebeests,” one hydrologist told me. Although federal funds were available, the towns in the valley weren’t rich and never had the money to pay their share for a replacement. Decisions about levee updates — which are sorely needed in much of the state but are currently governed by a hodgepodge of regulations and funding schemes — are prioritized in part according to the value of the property to be protected. This too often leaves low-income areas high and dry, or, more accurately, low and wet. “It’s not the same as redlining,” Fisher said, pausing as if to consider whether he agreed with his own statement. “But it is a systematic problem if you have a decision process that essentially writes off poor people.” To protect the most vulnerable communities, water experts have begun pushing the state to set much higher minimum standards for all levees. But that would take billions of dollars, and the political will to spend them.
The Pajaro Valley isn’t attached to the large canal system on the other side of the coastal mountains. (The idea of building a connection was floated, but local critics saw the cost as a public subsidy for corporate farms and defeated it.) This means that there’s already no infusion of water from outside the natural watershed, unlike in Southern California, which for decades has pulled large quantities of water from the hugely overdrawn Colorado River and is beginning to face a future of difficult cuts. There’s also no access to snowpack from the Sierra — a reality that will eventually and painfully come for the rest of the state as Sierra snowpack declines precipitously over the coming decades. “That’s more water than is stored behind all the dams in the state!” Fisher said.
Source link: https://www.nytimes.com/2023/05/31/magazine/california-floods-droughts.html