—Oceanic conditions drive continued drought, relief unlikely
The situation in California is dire. That hardly needs to be reiterated as reports of the next-to-nonexistent snowpack saturate the mainstream media as well as industry outlets. But the questions of “why?” and “when will it stop?” get less attention.
While the question of “why?” has some possible answers—acts of God/nature, climate change, natural variation, man-made mismanagement, etc.—the forward-looking concepts are harder to pin down. But before looking to the future, first look to the present.
According to the most recent California drought report, roughly a third of the state’s water regions saw no precipitation from Mar. 9-16, and the “wettest” region (Shasta Dam) saw just over a half-inch. Water yearto-date precipitation (Oct. 1, 2014-Mar. 16, 2015) are very low with the driest region (Riverside) seeing less than 4 inches, while the wettest region (Shasta Dam) saw just over 46 inches.
The statewide average for snowpack—the source from which a good portion of the state gets its water—was 17 percent of the to-date average, and only 16 percent of the expected April 1 total.
“The state must gain significant snow over the second half of March to avoid ranking as the lowest early April snowpack in historical records,” suggested the report hopefully.
The state’s reservoir levels are also concerningly low, according to the report:
• Castaic Lake 29 percent of capacity;
• Don Pedro 43 percent of capacity;
• Exchequer 9 percent of capacity;
• Folsom Lake 59 percent of capacity;
• Lake Oroville 50 percent of capacity;
• Lake Perris 37 percent;
• Millerton Lake 39 percent of capacity;
• New Melones 25 percent of capacity;
• Pine Flat 17 percent of capacity;
• San Luis 68 percent of capacity;
• Lake Shasta 58 percent of capacity; and
• Trinity Lake 48 percent of capacity.
According to the most recent drought monitor, almost 40 percent of the state is in the worst level of drought. Those heaviest levels of drought are centered on the highly productive central valley in the middle of the state. Most of the counties that make up Central California have been in an unbroken state of exceptional drought for over a year.
Despite many of the fantastical reasons offered for the extended Californian drought—now into its fourth year—the actual reason is more down to earth. The short story: It’s natural.
“The current drought is not part of a long-term change in California precipitation, which exhibits no appreciable trend since 1895. Key oceanic features that caused precipitation inhibiting atmospheric ridging off the West Coast during 2011-14 were symptomatic of natural internal atmosphere-ocean variability,” read a December 2014 report led by the National Oceanic and Atmospheric Administration.
Effectively, a large “ridge” of high pressure in the atmosphere developed over the eastern North Pacific Ocean as a result of anomalies in Pacific—and perhaps even global—ocean temperatures.
“It seems those ridges occur as a response to particular patterns of ocean surface temperatures around the world,” explained Dr. Richard Seager, professor and researcher at the Lamont Doherty Earth Observatory of Columbia University.
“We do think that the pattern of sea surface temperatures in the tropical Pacific is very important, but it could be that other influences in other parts of the Pacific—and maybe even the Atlantic—could be involved. That’s a research topic we’re working on right now. But it’s remarkably similar, this January and February, to what happened the previous winter.”
Sea surface temperature anomalies can impact the heating of the atmosphere above. This can trigger high pressure ridges and low pressure “troughs” to develop and extend around the planet.
The atmosphere works similarly to water or other matter; the higher the pressure on it, the denser it is and the harder it is for things to get through it. In this case, warm sea surface temperatures in specific parts of the Pacific helped create the high pressure ridge off the West Coast. This diverted winter storms up and away from the West Coast of the U.S. for the rainy seasons of 2011-2014 and in January and February of this year. As a result, California has missed out on rain.
In an email correspondence with WLJ, Dr. Michael Anderson, California State Climatologist with the Department of Water Resources, laid out the history of the current situation.
“We are currently in year four of our current drought. In the first year of the drought, low precipitation in winter was offset to a fair degree by spring precipitation and a late jump in snowpack. The second year started strong with a series of atmospheric river events in November and December impacting the northern part of the state. After the New Year, 2013 proceeded to be record dry which led to water year 2013 (Oct. 1, 2012-Sept. 30, 2013) being below average again with a very dry spring and low snowpack. Water Year 2014 and Water Year 2015 to date have been dry and warm with record low snowpacks and record warm winters.”
Though there are some similarities this year with last, there are also differences.
“This year is different than last year in terms of how the circulation set up and evolved over the course of the winter. Last year the ridge formed and entrenched itself quite strongly. This year we started into December with a nice strong jet stream and good flow into California. … Late in December the jet stream developed a split flow with one branch going north near the border of the U.S. and Canada and one branch going south into Baja California.”
Anderson summed up the situation simply.
“While the atmospheric flow patterns were different between last year and this year, the dry conditions for long stretches were similar.”
When will it end?
The answer here is hard to give in more ways than one. Of course no one can know the future, but what information there is isn’t hopeful.
Most—though not all— wet winters in the Golden State come hand in hand with El Niņo events. Earlier in the winter when the NO- AA report was being finished, it looked as though there might have been a weak El Niņo coming. The El Nino fizzled in December 2014, however, and California’s rainy season is just about over.
“We are getting into the second half of March here and the weather forecast models do not show any indication of significant precipitation for the rest of the month,” wrote Anderson. “I do not expect much more precipitation for this water year.”
Seager was of a similar mind.
“For this winter, rain and snow is pretty much over. You can get a bit in the remainder of March and a little bit in April, but for agricultural and ranching operations now through the end of November, pretty much all the water has come out of the sky that is going to, because it just doesn’t rain there after April.”
Though it is cold comfort, the early—and thereby questionable—models suggest an El Niņo event could develop for the 2015/16 winter.
“The climate models are again predicting that maybe there will be a weak El Niņo event this coming winter. But we can’t reliably predict El Niņo—or the opposite La Niņa—events from March through to the end of the winter. There’s a so-called predictability barrier in the spring where you have to wait until you pass April and May and into June before the seasonal predictions get rather skillful for the tropical Pacific for the coming winter. So we’re not putting much faith in those forecasts right now.” — Kerry Halladay, WLJ Editor