In the Talmudic parable of Honi the Circle Maker, the drought-stricken people of Jerusalem send up a prayer that God should deliver them rain. And sure enough, after a few false starts, he does. Except that once the rain starts, it won’t let up. It pours and pours until the people are forced to flee to higher ground, their homes flooded by the answer to their prayer.
That, minus the whole divine-intervention part, is roughly the situation that California currently finds itself in. After years of virtually unremitting drought, the state is now suddenly, tragically, swamped with an overabundance of water. Over the past couple of weeks, a series of intense storms has caused massive, widespread flooding. On Sunday evening, the president declared a state of emergency, and by the next day, more than 90 percent of the state’s residents were under flood watch. At least 17 people have died—that number is likely to rise—and tens of thousands more have been forced to evacuate. When the storms finally subside, the cost of the damage is expected to exceed $1 billion. But we still have a ways to go: Weather forecasters expect the heavy rain to continue for at least another week, along with lightning and hail. Tornadoes are not out of the question.
The flooding is the product of a weather phenomenon known as an “atmospheric river,” a long, thin channel of water vapor like a river in the sky. Atmospheric rivers funneled in from the Pacific are fairly common in California and are not in and of themselves bad news. Each year, the state depends on them to replenish its reservoirs ahead of the summer months, when it sees hardly any rain at all. Daniel Horton, a climate scientist at Northwestern University, told me that atmospheric rivers often supply more than 50 percent of the state’s annual water.
What’s unusual and problematic about the current situation is the atmospheric rivers’ frequency. “It’s definitely too much of a good thing,” Horton said. In just the past two weeks, six have made landfall in quick succession, delivering torrential amounts of rain to a state unaccustomed to dealing with so much water so fast. Three more rivers are on their way. “It’s often true that we’ll get one, and then a few weeks later we might get another one, and a few weeks after that we might get another one,” Peter Gleick, a climate scientist and a co-founder of the Pacific Institute, told me. “It’s unusual to see the persistence and the intensity of the storms we’re seeing now.”
It’s no surprise that climate change has likely played a role in all of this. California has always had something of a “boom-or-bust hydrological economy,” Horton told me, but the booms are getting even wetter and the busts even drier. As the atmosphere warms, it’s able to hold more and more moisture—this is why hand-dryers blow warm air, to maximize the amount of moisture that air can wick off your skin—and atmospheric rivers grow wetter and wetter. When they make landfall and deposit that moisture in the form of precipitation, the resulting storms are more intense.
Those shifts, Gleick told me, have thrown off the historical patterns that reservoir operators rely on to make crucial decisions. The trick is to walk the delicate line between ensuring that enough water is stored by the time the dry season rolls around and ensuring that too much water isn’t stored too soon, which can lead to flooding. “We have to think about operating the reservoirs differently,” Gleick said. “They’re designed and operated for yesterday’s climate, not for the climate of today or tomorrow.”
Climate change may also be contributing to the chaos in a slightly more roundabout way. The connection between warming temperatures and California’s longer, deadlier, more destructive wildfire seasons has been well documented in recent years. And even after the last embers are extinguished, wildfires alter the land they’ve burned for years to come. Torched plants leave behind a waxy, water-repellent film that renders fire-scarred soil less absorbent, Horton told me. Fire, as a result, leaves California more prone to flooding. And by burning away the trees and other vegetation that stabilize the soil, it makes floods more likely to trigger landslides.
This past fire season was blissfully quiet. But against that background, California’s current plight can feel in more than one way like a very dark punch line to a not-very-funny joke. What do you get after a summer of respite from deadly wildfires? A winter of catastrophic flooding. And what do you get after years of desperation for water? So much rain that you’ll pray it will stop.