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Winter storms in California's mountains drop record-breaking amounts of snow

ARI SHAPIRO, HOST:

This fall, California has been in a statewide drought emergency, but the month of December has delivered a surprise - a parade of winter storms blanketing California's mountains with record-breaking amounts of snow. UCLA climate scientist Daniel Swain is tracking the storms. Welcome.

DANIEL SWAIN: Thanks for having me.

SHAPIRO: How does this snowfall stack up to previous years?

SWAIN: Well, for the season to date, the numbers are pretty impressive, especially for the month of December where a couple of sites in the Sierra Nevada have seen more snow than in any previous December in the last 50 years or so.

SHAPIRO: Wow.

SWAIN: So obviously those are pretty big numbers.

SHAPIRO: Is that enough to wipe out the drought that California's been in for the last couple years?

SWAIN: On its own, it is definitely not enough to end the drought. Although, the good news is it does bring a lot of short to medium-term relief. So the drought conditions that were historically severe just a few months ago are now much less acute. And how much further drought relief there is is going to depend on how the rest of the season goes as well as how warm next year is.

SHAPIRO: Could it also make a difference for wildfire season?

SWAIN: It certainly could. It's especially good news that there's been this much water and precipitation that fell as snow instead of rain because, well, for one, snow accumulates in snowpack. It doesn't melt immediately and runoff into rivers, lakes and streams immediately, which means that when it does melt later in the season, it has a greater potential to replenish the water in the soil column gradually in a way that's maximally beneficial, as opposed to all of it just running off immediately as rainwater when it falls. So it is really good that this is occurring as snow rather than rain, and that may help us out in the year to come with wildfire risk because we know that especially in the forest - in parts of California and the Sierra Nevada - one of the strongest links to climate is how dry the soil conditions are and therefore how dry the vegetation can become. So the more snow we get during the snow accumulation season, usually the better off we are in the summer that follows.

SHAPIRO: What about conditions in the West generally? I know that the region as a whole has had it even worse than California. It's been described as the driest period in a thousand years. This has been an ongoing drought for 20 years or so. Is this snowfall going to help the West as a region?

SWAIN: Well, it's important to keep in mind that all of this really heavy snowfall has been pretty concentrated in the coastal - the Pacific coastal states. But the broader picture remains that the Southwest and the interior west is still experiencing what many scientists have referred to as a megadrought. This is sort of a bigger and broader phenomena across many states affecting really the entire Colorado River watershed. Of course, that is still important for California because much of the population of California, especially in the southern part of the state, receives a significant fraction of its water from the Colorado River. So it very much matters, and this winter is certainly not relieving the drought in the interior West. The snow drought is a little less acute than it was a few months ago, but on average, conditions have still been warmer and drier than average for the season to date outside of California.

SHAPIRO: So what do you think the rest of the winter is going to look like?

SWAIN: I think it's important to keep in mind that the rainy season is not even half over in California. And to date, we're off to a much better start than we were in any of the previous few years. So although, you know, the statistics are great right now - we're over 150% of average for the calendar date so far - we still need to see what happens during the second half of winter to determine just how much drought relief we're actually going to have heading into next summer. And there are some indications that the second half of the season will not be nearly so cold and wet. In fact, it could be on the drier side. So we will have to wait and see. But I am pretty optimistic, I would say, that, you know, the severity of the drought come the spring and summer will not be as high as it was last year.

SHAPIRO: Daniel Swain is a climate scientist at UCLA and the Nature Conservancy. Thanks a lot.

SWAIN: Thanks again for having me. Transcript provided by NPR, Copyright NPR.