OOver the span of two days, dramatic scenes of the dry landscapes and wildfires that defined the California summer were replaced by rivers, floods and mudslides as a historic rainstorm – considered a Category 5 atmospheric river – hit the state.
For scientists, the storm – while shocking in its magnitude – came as no surprise. It was clear that the climate crisis would intensify the extremes between wet and dry seasons, but many wonder if this weather boost is a foretaste of disasters to come.
Steven Ostoja, director of the United States Department of Agriculture’s California Climate Hub, said that while climatologists expected changes of this intensity, it was nonetheless surprising to witness them. Just days before the storm, the state capital, Sacramento, where Ostoja is based, set a record of nearly 200 days without measurable rain. “All of a sudden it’s like, my God. I have never seen it rain so hard outside the Belizean rainforest, ”he said.
Questions remain, however, as to whether the downpour will dent the ongoing drought, which has seen many state reservoirs drop to historically low levels.
The storm brought welcome gains. Lake Oroville rose 23 feet, soaking up hundreds of thousands of acre-feet of water. But even this increase amounted to a modest change, from 22% to 26% full. Shasta Lake – the largest in the state – added just 1%, from 21% to 22%. Most California reservoirs are still well below what they should be, even after tens of billions of gallons have been flooded. About 3 feet of snow has fallen in the Sierras, but unless temperatures stay low for the rest of the fall, the snow might not stay long.
Even the thirstiest landscapes were ill-equipped to absorb heavy rains, and it’s too early in the season for much of the water to be stored as snow. To have a real impact on drought, California needs a wet winter. A big storm – even a huge one like this – will not be enough to turn the tide.
“A water storm this early in the year doesn’t predict the rest of the winter storm season,” said Michael Anderson, climatologist in the state’s Department of Water Resources. La Nina, he noted, referring to a weather model that generally brings more variability with less rainfall over the southwest, heralds a return to dry conditions in California after this system has passed.
“This storm was historic in nature in magnitude,” he said, but it takes a lot more to pull the region out of the drought, especially in areas like the central and southern regions which have barely benefited from the storm.
The rain, however, brought notable good news – it put out the still smoldering wildfires in the state. Almost 2.5 million acres have burned in California so far this year according to Cal Fire, nearly double the five-year average, but scientists say this storm will likely alleviate any future hell.
“This storm is expected to put a definitive end to the wildfire season in northern California,” said Park Williams, climatologist at the University of California at Los Angeles. In Southern California, which has not been soaked to the same degree, the picture is not so clear. But it is full of hope.
“I think it is probably still too early to rule out the possibility of [a southern California] November wildfire, if the next two to three weeks are hot and dry and followed by a strong event in Santa Ana, ”Williams continued. “But despite that uncertainty, this rain event certainly dramatically increased the odds that the fire season was over in Southern California as well. “
While this year’s fire season may come to an end, this winter sets the stage for the one to follow. More precipitation is needed to ensure that another bad burn is not around the corner.
The state is expanding its weather extremes, experiencing stronger storms interspersed with periods of intense drought. The last historic drought, which spanned between 2012 and 2016, was followed by the wettest year in California history in 2017. Two years later, in 2019, the state had its fifth-best snowpack. In 2020, the cycle continued, and after a winter without much precipitation, 2021 delivered a more catastrophic drought.
“California can tip over in an instant,” said Andrew Hoell, a meteorologist at the National Oceanic and Atmospheric Administration’s Physical Sciences Laboratory, noting that even during the rainy season, the climate remains fairly dry. That’s why a storm usually won’t do the trick. “You need a constant supply of humidity on a fairly regular basis during the rainy season to have a real impact on your ecology in the field ”, Hoell said, especially when it comes to regrowing parched vegetation.
Since California typically only receives rain for a period of three to four months each year, the rainfall for the next few months will determine the effects for the next year or more.
USDA’s Ostoja said he views these extreme events as system resets, testing resilience to changes that otherwise occur in more subtle ways. These intense weather events can draw attention to the developing crisis he and other scientists are seeing in the data.
But “it really remains to be seen,” said Ostoja, of the role this storm will play in the months to come. “We’re just cleaning it up now,” he added, noting that it’s too early to know the longer-term dynamics. “Of course, we all hope it’s the start of a rainy winter – but the background information suggests otherwise. “