Any sign of precipitation in the forecast is a welcome sight for Californians these days. But with temperatures this winter, California鈥檚 snowpack may not reach the heights it could.
Getting snow in the Sierra Nevada Mountains is crucial to the state鈥檚 water supply. But scientists say as the climate continues to warm, more precipitation will fall as rain instead of snow.
鈥淣ot all precipitation is created equal,鈥� said Kelly Redmond, who studies the snowpack at the Desert Research Institute in Reno.
Both snow and rainfall end up in the same place in California, feeding its . The key difference is timing.
鈥淲hen it falls as snow, it stays there,鈥� said Redmond. 鈥淚t鈥檚 like a free reservoir. It doesn鈥檛 run off, doesn鈥檛 cause floods.鈥�
The Sierra snowpack melts just as California鈥檚 dry season begins.
鈥淚t releases slowly in the spring, and shows up in the rivers and in our faucets in the summer months,鈥� he said.
This timing is critical, Redmond says. The snowpack feeds about a third of the California鈥檚 water supply. If it fell as rain instead, water managers would need to find a way to store it in reservoirs in the winter until the dry summer months.
Record Warm Winter
State officials, understandably, keep a very close eye on snow levels, doing in the Sierra.
Currently, the snowpack is its best in years 鈥� . But last year at this time, it was just 21 percent. Dry weather was the main culprit to blame, but so was record-breaking warmth.
Last year, for the first time ever recorded in the Sierra, the coldest winter temperatures were above freezing on average.
鈥淚t doesn鈥檛 take much warming to switch from rain to snow,鈥� said Redmond.
California鈥檚 snow is already nicknamed 鈥淪ierra cement,鈥� because it鈥檚 known for being wet and heavy.
鈥淚t鈥檚 almost ready to turn to rain,鈥� Redmond said. 鈥淚t鈥檚 not like the powder you get in Utah and Montana and Colorado, which are at higher altitudes.鈥�
For every five degrees of warming, the freezing point of a storm, or the altitude of the 鈥渟now level鈥� as it鈥檚 called, will rise by a thousand feet, driving the snowpack higher into the mountains.
If rain falls on top of snow, it diminishes the snowpack further by melting it and producing heaving runoff.
鈥淥verall the freezing level in the Sierra Nevada has been going up,鈥� said Redmond. 鈥淚t鈥檚 been more in the spring. What this means is that melting is starting to occur earlier at higher altitudes and runoff is starting earlier.鈥�
Future of Warming
鈥淚 think this has been kind of a wake up call,鈥� said Dan Cayan, who studies climate change at the Scripps Institution of Oceanography and the US Geological Survey. "The last couple years were extraordinarily warm and I think to some extent those are models for what we might expect in the future,鈥� he said.
Cayan says California鈥檚 snowpack has already shrunk by 10 percent on average since World War II, a trend that is likely to continue as the climate warms.
鈥淏y the end of the century, if we鈥檙e lucky, we鈥檒l only lose half,鈥� said Cayan. 鈥淎nd if we鈥檙e unlucky, we could lose more than that. We鈥檙e in an era of unprecedented changes.鈥�
Whether California will get more or less precipitation overall with climate change is something that鈥檚 been debated, but a indicates that periods of dryness could increase.
Researchers found that the low-pressure weather systems that typically bring rain to the Southwestern US during the last three decades.
鈥淒roughts in the Southwest, specifically in California, are getting more intense and can last longer than in the past,鈥� said Andreas Prein of the National Center for Atmospheric Research, who led the study.
Preparing for More Runoff
鈥淚t鈥檚 a big deal,鈥� said Mark Cowin, director of California鈥檚 Department of Water Resources. 鈥淚t really does change the dynamic.鈥�
To prepare for a future with more extreme winter runoff, some have called for expanding California鈥檚 system of reservoirs.
鈥淥f course, there鈥檚 always been interest in dams,鈥� said Cowin. 鈥淭hey鈥檙e big. You can see them. But the fact is we鈥檙e not going to appreciably change the amount of reservoir capacity we have in California.鈥�
Aside from a handful of proposed projects, there are not many good locations left for dams, he says.
Instead, Cowin says the state will need to look at other options, like storing more water underground through groundwater banking, preparing for floods and using water more efficiently.
Those options will also take substantial financial investment.
鈥淲e could spend a hundred billion dollars over the next decade or two pretty easily,鈥� Cowin said. 鈥淓ven more than that.鈥�
California鈥檚 recent water bond could help with that, but at just $7 billion dollars, it鈥檚 really (and here comes the water metaphor) only a drop in the bucket.
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