Will La Niña send B.C. into a winter deep freeze?

“The only logical explanation for those were sea-surface temperatures,” MacDonald said. “When you have anomalies in the sea surface”¦it changes the storm track. And there are parts of the continent that are going to get more precipitation and parts that will get less precipitation.”

The Colorado River Basin has experienced a dramatic reduction in water levels because of a decade-long drought. MacDonald said that Lake Mead, the largest reservoir in the United States, has fallen about 39 metres since January 2000.

“Right now, it’s less than three metres above the level that would be a Level 1 water-shortage declaration, which has never happened before in history,” he noted.

La Niña could exacerbate the drought in the U.S. Southwest, whereas it’s likely to lead to a sharp increase in moisture this winter in B.C., according to MacDonald. “I think there is a chance of a 40-percent-above-normal precipitation,” he suggested.

One of MacDonald’s UCLA colleagues, geographer Laurence C. Smith, told the Straight by phone that continents in the northern hemisphere get colder the farther east you go. “If you look at prevailing wind directions, they’re generally from west to east,” Smith said. “The oceans have a modulating effect. They’re relatively warm compared to continental land masses.”

In his recent book, The World in 2050: Four Forces Shaping Civilization’s Northern Future, Smith cites MacDonald’s research in noting that two “perfect droughts” lasting five to seven decades could have occurred in the American Southwest in the Middle Ages. “Not only did the medieval climate warming increase the drying of soils directly,” Smith writes, “it may also have altered an important circulation pattern in the Pacific Ocean, by shifting relatively cool water masses off the western coast of North America for many decades at a time (this would be a prolonged negative phase of the so-called ”˜Pacific Decadal Oscillation,’ an El Niño–like oscillation in the northern Pacific that currently vacillates over a 20-30-year time scale).”

This raises question of whether or not above-average precipitation could continue in B.C. well into the future. And, if so, does that mean ski resorts at higher elevations could look forward to more snow, even as the province gets hotter because of climate change?

MacDonald told the Straight that it’s difficult to predict what’s going to happen to the El Niño–La Niña system in the 21st century. “It seems that sea-surface temperatures in the Pacific and in the Atlantic have long-term variations,” he said. “We still don’t understand what are the drivers, what triggers them.”

On a lighter note, MacDonald noted that in the winter, Canadians often lust after the clear blue skies and sunshine of the U.S. Southwest. However, during summer, when U.S. reservoir levels fall, he claimed that Americans look enviously at all that water in Canada. “Don’t squander it and don’t waste it,” he advised. “It’s an increasingly precious commodity.”