This story is part of our series Water at Risk, which looks at some of the risks to the water supply facing parts of Canada, South Africa and the Middle East. Read more stories in the series.

As conservationists and organizations around the globe mark World Water Day Thursday, some scientists are warning that Canada is not immune to water shortages and periods of drought.

All regions should prepare for them to some extent, says John Pomeroy, professor of geography and director of the Centre for Hydrology at the University of Saskatchewan.

Predicting drought is difficult because, although we are able to predict changes in temperature relatively well, tracking potential changes in precipitation and weather is more difficult, he said.

Barrie Bonsal, a research scientist with the Water Science and Technology Directorate of Environment Canada, has been working on a Canada-wide study of the likelihood of drought.

The study, which looks at 29 climate change models to the year 2100, forecasts how much moisture different areas of Canada can expect if greenhouse emissions grow unchecked, but also if they are successfully reduced.

"Drought is a natural part of our climate. We've had it in the past and will see it in the future," he said.

Faced with global warming, "what we want to know is whether the precipitation changes will be able to offset higher temperatures," he said.

The climate moisture index measures the difference between annual precipitation and the potential loss of water vapour from a landscape covered by vegetation. Below the zero line (yellow, orange and red areas), the conditions may be too dry to support a forest. This projection is for the years 2071-2100 assuming the world continues to increase greenhouse gas emissions. (Natural Resources Canada/CBC)

These are the parts of the country most at risk:

Prairie provinces

All three Prairie provinces, stretching from the Rocky Mountains to the shore of Hudson Bay, are vulnerable to drought, says David Price, a scientist for Natural Resources Canada who models climate change outlooks.

Winds over the Pacific Ocean pick up moisture and sweep over British Columbia until they hit the Rockies, when the moisture falls as rain or snow, Price says. A little of the moisture makes it over the mountains, but as summer temperatures rise, the risk of drought across Alberta, Saskatchewan and even Manitoba will grow, he said.

Southern parts of those provinces are vulnerable to drought, Bonsal agrees, and droughts could become more severe later in the century. Alberta will be particularly vulnerable as glaciers in the Rockies melt, ending a formerly reliable source of water.

Takakkaw Falls in Yoho National Park, in the Rocky Mountains near Field, B.C., is more than 300 metres high. A reduction in moisture crossing the mountains from west to east would leave the Prairies dry. (Adam Kealoha Causey/Associated Press)

Pomeroy points to Palliser's Triangle in the southwest Prairies, which stretches from Calgary and Regina to the U.S. border, as a region that could potentially be in trouble.

The name comes from Irish explorer John Palliser, who was tasked in the 1850s with exploring Western Canada for suitable places to settle. He concluded that the region should be avoided because it was too arid.

Pomeroy says people who live in Palliser's Triangle are used to its dryness and have adapted — for instance, building farms father apart — but prolonged and more severe dry spells would place an even greater strain on water supplies.

South-central British Columbia

British Columbia's Okanagan Valley is one of the driest places in Canada, and agriculture puts pressure on water supplies.

Climate change could mean even hotter summers in the region, making it more vulnerable to drought.

"Most models show it getting drier toward the end of the century," said Bonsal.

British Columbia has been dependent on snowpack to provide moisture through the spring and summer, but it may get more rain in winter, which would run off the land rather than melting slowly as snow does, Bonsal said.

Then early springs and hotter summers could mean the moisture dries up more quickly.

The Lower Mainland of B.C. is accustomed to seeing lots of rain, but with places like the lower Fraser region and Vancouver Island seeing less of it, they'll have to rely more and more on water reservoirs, according to Pomeroy.

However, since those regions don't usually have to rely on reservoirs, he says, the ones they have aren't adequate to offset the lack of rain. In fact, the shortage has prompted water restrictions in the province and instances of hydrological drought, which is when lakes, rivers and ground water supplies are depleted.

Yukon and Northwest Territories

In Yukon and Northwest Territories, there is not a large population to draw on water supplies, nor are summers hot enough to evaporate moisture from the ground, says Price.

That could change with global warming. "The impact of climate change is being felt rapidly in the far North," Price said. "We could see a dry winter followed by a hot summer that would make drought quite possible."

Bonsal points to the earlier springs and longer periods of warmth the North is already experiencing. He predicts not much change in Yukon and N.W.T. to about 2065, but says whether the area is vulnerable will depend on weather in individual seasons.

Ontario and Quebec

Southern parts of Canada's two most populous provinces are mainly protected from drought because of the Great Lakes, which create their own wet weather systems. Climate change models vary in their predictions of whether water levels in the Great Lakes will rise or fall as weather patterns change.

A forest fire burns northeast of Winnipeg in 2017. It only takes a couple of summers of low rainfall for forests to become tinder-dry. (Judy Klassen/Facebook) But there still could be a need for water restrictions if demand exceeds supply, Bonsal said.

Northern parts of Ontario and Quebec are less influenced by the Great Lakes, and their forests could be threatened.

"You only need a couple of years of very dry conditions to make those forests tinder-dry," Price said. That means elevated risk of forest fire.

Be ready for dry periods

By contrast, Atlantic Canada and eastern Quebec are predicted to become wetter as the century progresses, under most climate change models.

Pomeroy says Canadian municipalities should be looking at ways to store water and encouraging reduced consumption.

"Every community and province needs a drought plan — how they will deal with water shortages to maintain supplies to priority users and how they will apportion water when it runs short," he said.

"We like to think of ourselves as a water-rich nation. That's not quite the case anymore."

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