California is being battered by what the National Weather Service calls a “seemingly never-ending march” of a powerful storm system that began in late December and is still continuing.known as rivers in the atmosphere, which are long, narrow streams of water Unusually moist air across the ocean, capable of dumping large amounts of rain or snow upon landfall. While these storms bring most of the precipitation to the west, they also cause most of the region’s flooding, with associated economic losses running as high as $1 billion a year.
A string of storms this winter has killed more than a dozen people in California and put tens of thousands under evacuation orders and observations. Rainfall on December 31, 2022 reached 5.5 inches in downtown San Francisco and flooded all six lanes of Highway 101 in South San Francisco. On Jan. 8, torrential rain and 70 mph winds left more than 345,000 people without power in the state capital, Sacramento.
More atmospheric rivers are expected in the coming days, sparking fears across California and catastrophic mudslide The latest wildfires have left 21 burn scars around the state. Its governor, Gavin Newsom, declared a state of emergency on Jan. 4, and the White House issued a California presidential emergency declaration on Jan. 8.
To learn more about why these storms hit California, and their potential dangers and benefits, scientific american Interview with extreme weather expert Katerina Gonzales, who studied atmospheric rivers as a graduate student at Stanford and is now a postdoctoral associate at the University of Minnesota.
[An edited transcript of the interview follows.]
Forecasters didn’t expect California’s winter to be so wet. why?
We often try to use El Niño and La Niña — large climate patterns in the Pacific Ocean — as surrogate indicators for forecasting. The simple narrative is that El Niño is wet and La Niña is dry. This is the third year of La Niña, and expectations have been set for the previous two years of less wet winters.
Why didn’t this year’s forecast hold up?
Simple narratives are not necessarily true. Northern California is on the cusp of a wet and dry pattern. It’s kind of bullshit; it’s fine either way. El Niño and La Niña could tip the scales towards wetter or drier, depending on what else happens along the coast.
What else is causing these powerful storms in California? Are they unusual?
There’s all sorts of chaos going on in the atmosphere, but sometimes it stays in a certain configuration for a while — so the storm track gets stuck. A storm path is a wind current, like a jet stream, that carries moisture away from west to east. La Niña can push the storm track toward Northern California, and it’s now favoring atmospheric river landfall on this part of the coast.
Atmospheric rivers come one after another, really powerful and moist. This convergence is at the heart of the problem. It’s unusual to have so many storms and they’re super juicy.
Mountains often squeeze water from rivers in the atmosphere. But last week, a lot of moisture from California’s storms reached Minnesota, dropping a foot and a half of snow. There is too much moisture in the system; it is not normal to have this much.
What is the effect of this atmospheric river parade?
The first storm saturates the soil—it gets soaked like a sponge, soaking up all the water it can—and any more storms will lose it. Rivers, creeks and reservoirs are also fuller, so we may have floods.
The silver lining is snow. It’s January, it’s cold, it’s snowing most of the time in the mountains, and the snow is getting thicker. Layers of fresh snow. If this were March, it would be warmer and we would have snow. That would melt snow, reduce the amount of water we store and cause flooding.
California has been in drought for three years in a row. finished?
We are still in a drought. Snow packs and reservoirs are fine, so for ground storage, we’re doing pretty well. But the aquifer remains depleted. Groundwater has to be recharged, which takes a long time. We cannot rely on atmospheric rivers to save us. California has wet and dry poles – that’s our current reality and our future. We should prepare.
How is climate change affecting atmospheric rivers? How is California preparing?
As the climate changes, atmospheric rivers become more intense because they hold more moisture. For a long time, I thought we should focus on more science to improve forecasting. But we need to adapt to the climate change we have already started. We cannot predict how we will escape the larger atmospheric rivers.
We must invest heavily in green infrastructure that absorbs runoff naturally, such as floodplains, parks, and rain gardens. Our infrastructure was built for the climate of the 20th century and doesn’t exist anymore. More intense days are to come, and these storms are only a preview.
