It may not feel like it the morning after a blizzard, but Canada gets less snow than it used to — a lot less.
That’s the conclusion of scientists at Environment Canada, who have just published what they say is the most precise estimate of global snowfall yet.
“It seems like it should be easy, right? You just stick a ruler in the snow,” said Chris Derksen, a co-author of the study published Wednesday in the journal Nature.
But no.
Unlike rain, snow depth can vary widely over just a few metres depending on factors such as wind. As well, some snow is heavy with moisture and some is dry powder.
And the world’s network for snow observation is sparse, Derksen said. Add to that the difficulty of trying to estimate snow depth from satellite observations and you’ve got the beginnings of what has been a 15-year project for Derksen’s team.
“Snow is a tricky thing to measure,” he said. “We had quite a few data sets that estimated snow mass, but they were based on different techniques and they didn’t agree with each other very well.”
Working with Finnish colleagues, the federal researchers combined satellite data and on-the-ground measurements.
On average, they conclude, the world gets about 3,000 billion tonnes of snow every year.
But that’s not a static number, at least not in North America. Snowfall hasn’t changed much over Eurasia since 1980, but it is declining in Canada and the United States.
Over the last 39 years, snowfall in the two countries has dropped by about 4.6 billion tonnes a year. The paper is silent on how many shovelfuls that is, but Derksen said it’s about enough to fill almost two million Olympic-sized swimming pools with snowmelt.
The steepest drops are in the eastern part of the continent. Parts of the west have actually seen slight increases.
Derksen said regions with less snow aren’t necessarily drying out. Climate change has been shortening the season for a while, and some of what used to fall as snow now comes down as rain.
“The amount of precipitation is not decreasing.”
But snow is a lot easier to manage, he said.
“When (snow) melts, we can manage our reservoir levels and trap that meltwater. As soon as it rains, it runs off in streams.”
That difference has important consequences for big-city water supplies as well as flood threat management. The 2013 Calgary flood is an example of what can happen when unexpected heavy rains come early in the season, said Derksen.
The paper does have its uncertainties. It is unable to say much about snowpack in the mountains, for example.
But Derksen said the work goes a long way to understanding that most Canadian of elements. And it should help managers plan as snowfall changes along with the rest of the climate.
“What this study has tried to do is narrow that uncertainty.”
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