It may not feel like it the morning after a blizzard, but Canada gets less snow than it used to B次元官网网址� a lot less.

ThatB次元官网网址檚 the conclusion of scientists at Environment Canada, who have just published what they say is the most precise estimate of global snowfall yet.

B次元官网网址淚t seems like it should be easy, right? You just stick a ruler in the snow,B次元官网网址� 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 worldB次元官网网址檚 network for snow observation is sparse, Derksen said. Add to that the difficulty of trying to estimate snow depth from satellite observations and youB次元官网网址檝e got the beginnings of what has been a 15-year project for DerksenB次元官网网址檚 team.

B次元官网网址淪now is a tricky thing to measure,B次元官网网址� he said. B次元官网网址淲e had quite a few data sets that estimated snow mass, but they were based on different techniques and they didnB次元官网网址檛 agree with each other very well.B次元官网网址�

Working with Finnish colleagues, the federal researchers combined satellite data and on-the-ground measurements.

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On average, they conclude, the world gets about 3,000 billion tonnes of snow every year.

But thatB次元官网网址檚 not a static number, at least not in North America. Snowfall hasnB次元官网网址檛 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 itB次元官网网址檚 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 arenB次元官网网址檛 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.

B次元官网网址淭he amount of precipitation is not decreasing.B次元官网网址�

But snow is a lot easier to manage, he said.

B次元官网网址淲hen (snow) melts, we can manage our reservoir levels and trap that meltwater. As soon as it rains, it runs off in streams.B次元官网网址�

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.

B次元官网网址淲hat this study has tried to do is narrow that uncertainty.B次元官网网址�

This report by The Canadian Press was first published May 20, 2020

Bob Weber, The Canadian Press

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