Why Is California's Snowpack So High?

In California, the snowpack is at some of the highest levels in recorded history.

The state's snowpack accumulates in the Sierra Nevada—a mountain range that stretches for 400 miles from Northern California southward to the Great Basin. The snowpack, which melts into the state's reservoirs, provides about a third of California's total water supply.

The Southern Sierras, which stretch from San Joaquin and Mono counties to Kern County, have a snowpack level 257 percent greater than average for this time of year, according to data from the California Department of Water Resources.

The Central Sierra and Northern Sierras have also accumulated much higher snowpack levels than usual. The levels there are, respectively, at 218 percent and 168 percent of the average for this time of year.

The state has been in the grips of a drought for a decade, making these high snowpack levels particularly surprising. So what has caused these levels?

The state has seen an extremely cold and wet winter period. The beginning of spring also brought some severe storms that battered much of the state.

Karla Nemeth, director of the California Department of Water Resources, said in a statement at the beginning of March: "Thankfully the recent storms combined with the January atmospheric rivers have contributed to an above-average snowpack that will help fill some of the state's reservoirs and maximize groundwater recharge efforts."

Colin McCarthy, an extreme weather expert and content creator, said on Twitter that California is now set to have "its largest snowpack in recorded history."

Atmospheric rivers are the main cause of the wet weather that has hit the state. An atmospheric river is a corridor of concentrated, tropical moisture traveling through the atmosphere. Another atmospheric river is due to arrive in the state in the coming days. It is expected to bring 2 to 4 feet more snow, McCarthy said.

The problem is that these atmospheric rivers can do more harm than good when many come all at once. The atmospheric rivers bring accumulating snowpack, but the tropical moisture also causes it to run off.

With such a large amount of snowpack this year, this can cause severe flooding. Flooding can be worse in drought-stricken states when a certain amount of water descends on dry areas.

This is because the ground can become parched to the point where the water does not saturate the ground. This causes flashing flooding.

"So we still need more big storms for 2023 to be even an average year," hydrologist Roger Bales, a distinguished professor of engineering at the University of California Merced, previously told Newsweek.

"The Central and Southern Sierra indices are above the water-year average, which is good for water supply but potentially bad for flooding if we get a warm atmospheric river coming in that results in faster snowmelt," he said. "I also refer to the Northern Sierra index, because much of our water supply for Southern California and many irrigation users comes from that large, wetter part of the state."

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