So What Happens When All That California Snow Melts?

 A week or two ago, I wrote about how the healthy early March snow in Vermont slightly increased the threat of flooding this spring. 

Snowbanks along Interstate 80 in Donner Pass,
California recently. 

So what happens when 50 or feet of snow has to melt under the strong rays of the spring sunshine? 

I'm not sure, but unfortunately, Californians will soon find out. 

The storms are still rolling into California, maybe with less intensity and frequency than they did a few weeks ago, but regardless, bad enough. A warm atmospheric river recently melted a fair amount of snow in some of the blizzard-wracked foothills. That was enough to unleash some serious, damaging floods.

The Sierra snows should be just starting to melt by now. But snowstorms and continued below normal temperatures are continuing. Probably for at least another week or two. Instead of getting rid of some of the snowpack and its water, more additions are coming. 

At least another foot or two of new snow is expected in the Sierra Nevada mountains of California between this morning and tomorrow afternoon. 

The snowpack in the Sierra Nevada typically peaks around April 1. But forecasts indicate that peak might come later this year, as below normal temperatures and above normal precipitation are forecast to last in California at least into mid-April. 

The later we get into spring, the greater the chance a heat wave could strike. That would unleash a lot of water.

There's plenty of water in that snowpack, that's for sure!

As of the middle of last week, some of California's ski areas had received more than 650 inches of snow this season. That's more than 54 feet of snow. Most of that snow is still on the ground. 

The amount of snow in the Sierra Nevada mountains in California exceeds or will soon exceed that of the winters of 1969 and 1983, which until now had been the benchmark for the most snow you can get. 

The results probably won't be good. Especially if California flips to the kind of weather they've seen later in spring - very hot weather. 

As the Washington Post reports: 

"'It is important to understand that we are in uncharted territory,' said Jeffrey Mount, a senior fellow at the Public Policy Institute of California's Water Policy Center, in an email. 'The amount of water tied up in snow in the watershed is about twice the average amount of runoff in an entire year.'

FULL RESERVOIRS/NEW LAKES

When the 1983 snowpack melted, it flooded 100,000 acres of farmland and temporarily re-created a lake that had been drained generations earlier.    Lake Tulare, as it was called,  had been the largest west of the Mississippi, even bigger than the Great Salt Lake more than a century ago. But, it was drained for extensive farmland in California's Central Valley.

However, Lake Tulare partly reappears in especially wet and snowy years, so, it will probably re-appear this year, says that Public Policy Institute.

  It took two year after the 1983 event to pump out the water in temporary Lake Tulare and restore it to cropland, according to the Public Policy Institute.

If Lake Tulare comes back this year, as seems inevitable, it's not all bad. At least a small proportion of it will seep into underground aquifers, which have been over-pumped for decades to feed agriculture, mostly. 

What would have been better for California would have been a series of several winters that were somewhat wetter and snowier than average. That would have allowed reservoirs to fill, but not overflow. Several consecutive sort of wet but not overly soggy and snowy winters would have built back some of the depleted groundwater in California.  

Instead, California has had an epic winter.  Too much of a good thing. This winter's weather has definitely helped erase, or at least sharply dim the state's long-lasting drought. But a lot of this year's runoff can'r be saved up. There's too much of it.  

Reservoirs are filling up, and there's no capacity for storage

As the Washington Post reports, two reservoirs on the Tule and Kaweah rivers are full, so they can't take on any more water to prevent flooding downstream.  One city, Visalia in the San Joaquin Valley might suffer flooding as soon as this week as water is released from behind the dam on the Kaweah river.

Those two reservoirs mentioned above are relatively small.  The risk of flooding increases when some larger reservoirs fill up. 

A USGS site in the Sierra Nevada mountains '
of California overwhelmed with snow recently. 

Another problem is the scale of the snow and the runoff this spring. It'll take a lot of time to melt literally dozens of feet of snow. Which means high water flowing down from the mountains will last many weeks.

The state has many aging levees that have not been tested by weather like this in years, or even decades. It's one thing to rely on the levees to hold back water for a few days. The pressure of flooding lasting many weeks might be too much for the levees to bear. 

Of course, levees tend to be in worse shape and the most neglected in low income communities and areas without a thriving agricultural industry. Typical story of the haves and have nots. 

SACRAMENTO DANGER

A worst case scenario - pretty unlikely at this point but still in the realm of possibility - is a huge flood in and around Sacramento, California's capital.

As Dan Walters wrote in CalMatters.org earlier this month, Sacramento is at the juncture of two pretty big rivers, the Sacramento and the American. 

Walters explained that a bypass channel protects the city from the Sacramento River, as long as levees along the channel hold nicely. 

But, the American River is a bigger threat. There's a flood control dam upstream from Sacramento called the Folsom Dam/Folsom Lake.  It can store water and ensure moderate stream flows in Sacramento in ho-hum water years. 

However, this year, we'll see a bigger snow melt surge over the next weeks and months coming down from the Sierra Nevada range. Folsom Lake could well be too small to deal with such a long, sustained snowmelt flood.

The winter rains and snows in California have seriously dented, if not eliminated drought in much of the state. That, of course, is a good thing. But, as always, there's a downside. 

As Walters reported: "'I hope I'm wrong, but I'm afraid people celebrating the great snows in the Sierra Nevada are seriously underestimating the risk of spring flooding in California, including reservoir operators and state and federal managers,' Peter Gleick, one of the state's foremost experts on water, tweeted."

Warm atmospheric rivers - ribbons of intense moisture in the air that wring out tons of rain, hit California at mid-month. That melted a lot of the snow in the some of the foothills, mostly at elevations between 1,500 and 3,000 feet above sea level.

 Even though some rain came down in rather high elevations of the Sierra Nevada, those warm storms might have done more harm than good,

Winter rains actually don't melt much snow, but they do soak into the snowpack, making the amount of water primed to run off as melting in the spring that much more intense. 

As Daniel Swain, a climate scientist at UCLA's Institute of the Environment and Sustainability, told The Fresno Bee, California is now in uncharted territory.

Swain continued explaining to The Fresno Bee:

"'There is so much water stored in the southern Sierra snowpack, at or above record levels,' Swain told The Bee. 'And we haven't had a climate as warm as we currently do with a snowpack this large.' An early season heat wave, which has become a more occurred e in recent years 'could happen in the spring and could cause a lot of this snow to melt quickly.'"

Part of the reason why California had been in such an extensive drought in recent years is intense spring heat waves prematurely melted what little snowpack had accumulated in the Sierra.

So what happens if it's suddenly really hot and sunny in April and May this year?  Swain sounds nervous, as I would be.  

As in almost every other place, if temperatures are moderate in April and May, the snow melt in California would be gradual enough to prevent severe flooding. So, it's really a tossup as to whether the serious flooding the state has experienced will last into the beginning to the so-called "dry" season in May. 

Of course, California is also famous for its wildfires. The extreme snows and rains could make the fire season go either way. 

Above 6,000 feet, especially if the snow melt is gradual, it'll stay wet in the high spots through the bulk of the fire season. That would suppress high elevation fires, Swain told the Fresno Bee. 

The problem would come at lower elevations. All that rain is making plants, underbrush and such to grow exuberantly. If it's a hot, windy summer in California, all that new brush will dry out. So will the stuff that blew down in the high winds this winter. That could create a nasty fire season. 

It seems nowadays, any kind of weather creates a new crisis in California.