For California, where punishing droughts over the past two decades have withered crops and caused wells to run dry, it was another year of extremes. This time, they are the opposite.
It started with winter storms that drenched cities and towns, buried the Sierra Nevada in snow and caused the reappearance of a massive lake that had long since disappeared in the Central Valley. And it’s poised to pass another milestone this weekend, as Hurricane Hilary batters Southern California and its bone-dry inland deserts, which typically receive little rain a year.
It’s all quite a turnaround from the past three years, the state’s driest on record, when officials imposed strict controls to conserve water.
Hilary, which forecasters say could weaken to a tropical storm by the time it makes landfall in California, has no direct meteorological connection to storms from earlier this year. But, taken together, they reinforce a basic adage about California weather: There’s no such thing as a typical year — just too wet, or too dry.
“This year will be known as just a story of extremes that worked all year,” said Michael Anderson, California state climatologist.
In a warming climate, we should expect to see more of such extremes, says Dr. Anderson. However, “to have all of this happen in the same year, in and of itself can be extreme,” he said.
Precipitation varies throughout the contiguous United States from year to year more than California, and in southeastern California. The state’s Mediterranean climate — with hot, dry summers and cold, wet winters — means river-fed atmospheric storms that hit the state between November and March deliver most of the water it gets throughout the year. This diversity is a major factor in the state’s ongoing struggle to supply water to both its huge population and its agricultural sector.
California often receives more rain during El Niño, the recurring climate pattern associated with sea surface temperatures in the Pacific. But this past winter’s storms went through its opposite phase, La Niña. El Niño conditions arrived in late spring and are expected to continue into next year, which could mean another wet winter for California.
Also in the background: climate change. As societies burn fossil fuels and heat the planet, a warmer atmosphere can hold more moisture. This means that storms in many areas, including California, are more likely to be very intense.
Especially in the context of some other extreme weather that North America has experienced this year — an extraordinary heat wave in the Southern United States; wildfires exacerbated by heat and drought in Canada; heavy rains and flooding in Pennsylvania, Kentucky, Vermont and other regions — the storms in California fit a pattern, said Michael Dettinger, a hydrologist and climatologist at the Desert Research Institute in Reno, Nev.
Different atmospheric mechanisms play a role in each of these extreme events, he said. But “the relentless nature of these cumulative events certainly shows something deeper than the individual events, by which I imply climate change without a chain,” said Dr. Dettinger.
An unusual combination of factors leads Hilary to threaten Southern California, where a tropical storm has not made landfall in more than 80 years.
Pacific waters off the coast of Mexico became warmer than usual, which allowed Hilary to gain additional energy as it built up over the ocean. A heat dome over the central United States and a low-pressure system off the coast of California are also pushing the storm toward California and the Southwest instead of out to sea.
“From time to time Mother Nature lists everything,” says Dr. Anderson, the state climatologist.
The feast-or-famine nature of California precipitation means that even a very wet year like this can only boost water supplies so much before scarcity becomes a problem again.
“The reservoirs may be full, but the land is still dry,” said Jay Cordeira, an atmospheric scientist with the Scripps Institution of Oceanography, part of the University of California, San Diego. He pointed to increased wildfire activity this month, including in the state’s northern forests, where evacuations were ordered near the Oregon border.
Basically, California has “a baseline-drought climate punctuated by monsoons,” said Dr. Cordeira.
One way growers and landowners try to cope with these swings is by capturing water from rainfall and percolating it into the soil, where it can effectively be stored as a reserve. for later use. In principle, this could reduce flood threats to homes and communities while also helping to build a lifeline for farmers against future droughts.
But doing this on a large scale requires a lot of planning and infrastructure, including pumps, canals and basins. There are also knotty legal complexities: California dictates who can reroute water from streams and rivers, to protect the rights of people downstream.
State authorities have worked to help local water districts overcome these obstacles and replace their aquifers. Earlier this year, 92,410 acre-feet of potential floodwater was diverted underground in response to an executive order from Gov. Gavin Newsom, according to the state Department of Water Resources. (An acre-foot is the amount of water used by two to three households in a year.)
The progress is encouraging to see, said Philip Bachand, an engineer who works on groundwater recharge projects in various parts of California. But, he said, the state still needs to put more water into the ground each year if it has any hope of reversing the damage from decades of aquifer depletion and overuse. And the obstacles to doing so – logistical, technical, legal – remain great.
“I just don’t know if it will work in time,” he said. “I’m really worried about that.”
