Canada is among the world’s water-rich countries. But that reputation depends on something most Canadians take for granted: snow.

Across Canada, seasonal snowpack acts as a natural water reservoir. Snow accumulates during the cold months, storing precipitation until spring, when it melts and feeds rivers, taking the water downstream. This delayed release is one of the hidden pillars of Canada’s water, food and energy security.

Growing climate variability and long-term warming are reshaping how this natural storage system works. The risks are not always dramatic or sudden. Instead, they are emerging gradually and creeping across drainage basins through a phenomenon called snow drought.

Unlike meteorological droughts, snow droughts do not necessarily mean less precipitation. Instead, they reflect changes in how water is stored in snowpack and how quickly it disappears. Warmer winters increasingly produce rain instead of snow, trigger mid-season melting and shorten snow-cover duration. The result is less water storage during freshet, even in years that appear “normal” or even “wet” on paper.

Recent research across Canada and Alaska shows that usable water stored in snow is changing in complex and sometimes counterintuitive ways. While many northern and eastern regions show overall increases in snow water availability, significant and insignificant losses are emerging in critical western and southern regions, particularly mountainous headwaters that supply major downstream river systems.

Accounting for how much water is available in a snowpack is not trivial. Traditionally, water planners have relied on snow water equivalent (SWE), which estimates how much water would be released if snow melted instantly. This metric assumes snow is distributed evenly across the landscape. However, snow cover can be highly uneven, and warming winters are making snow cover even more patchy.

To better capture this new reality, researchers developed a new metric, Snow Water Availability (SWA), which estimates water stored only where snow actually exists on the ground. This approach provides a clearer picture of how much meltwater can contribute to water supply, particularly in mountainous regions and/or during seasonal transitions, where and when snow cover becomes fragmented.

Recent research across Canada and Alaska shows that usable water stored in snow is changing in complex and sometimes counterintuitive ways, writes Ali Nazemi.

While the study showed that from 2000-2019, SWA has actually increased across Canada and Alaska, losses are appearing in parts of western Canada, particularly within the Rocky Mountains area, a region that feeds major river basins supporting communities, agriculture and hydropower. Because upstream mountains act as water towers, small losses can propagate downstream through entire river systems, meaning headwater changes matter disproportionately. When significant declines in snow water from seemingly small areas combine with less significant but widespread declines downstream, they can influence water availability across a quarter of Canada, home to 86 per cent of the country’s population.

Climate variability plays an important role in changing SWA. This means snow drought risk does not increase uniformly across the country and can fluctuate from year to year. Large-scale ocean-atmosphere patterns, such as Pacific and Northern oscillations, can amplify or offset the effects of long-term warming. Regional manifestations of warming can also be variable. While in northern regions, warming-induced arctic sea ice retreat and higher atmospheric moisture capacity may increase snowfall, mountainous regions in Alberta and British Columbia experience accelerated melt and/or precipitation shifts toward rain. 

A creeping snow drought can affect a quarter of Canada’s land and 86 per cent of its population. The left panel shows the areas with decreasing annual snow water availability during 2000-2019. Significant and insignificant declines are shown by dark red and pink colors, respectively. The middle panel shows the affected drainage basins by decreasing snow water availability and categories them to regions that are highly vulnerable, vulnerable or at risk, depending on the nature of decline in snow water availability. The right panel shows population density in Canada’s drainage basins, showing how Canada’s populous areas are impacted by snow drought. Maps by Ali Nazemi

History shows how damaging snow drought can be. In 2015, extremely low snowpack across the Rocky Mountains reduced streamflow, stressed municipal water supplies and contributed to ecosystem impacts, including salmon die-offs linked to warm river temperatures. During the winter of 2011–2012, low snowpack across southern Ontario and Quebec contributed to historically low water levels in the Great Lakes and Saint Lawrence River, forcing emergency dredging and disrupting shipping.

What makes creeping snow drought particularly concerning is its slow pace. Small annual declines in mountain snow storage can accumulate into large water supply risks over time. Because river systems connect regions, snow losses in one location can cascade across entire drainage basins.

These risks are particularly relevant for the Prairies, where irrigation demand is closely tied to spring snowmelt, as well as for hydropower systems and interprovincial water agreements that depend on predictable river flows. Farther downstream, the Saskatchewan River Delta — the largest inland delta in North America — supports unique ecosystems and Indigenous communities whose livelihoods depend on regular flooding that replenishes wetlands.

The emerging science suggests Canada must rethink how it monitors and manages snow-derived water resources. Future water planning will increasingly require accounting for the changes in snow water and new diagnostic tools such as SWA to capture the growing importance of patchy snow cover and mid-winter melt events. 

However, snow water accounting is not free of uncertainty, even using SWA. To address this, researchers increasingly rely on merging multiple datasets to better quantify uncertainty and improve confidence in regional trends. While it has been shown that basin-wide uncertainty in annual SWA is marginal and manageable, the uncertainty can be large when looking at smaller regions, particularly during transitional seasons. This is due to the fact that each data source has its own strengths and limitations, and differences between them introduce uncertainty into snow assessments. 

Reducing this uncertainty inevitably requires better monitoring. While in-situ snow monitoring in Canada has been and will remain challenging, especially in northern and high-elevation regions, there are new opportunities to use satellite observations, in which Canada should strategically invest. We also need improved short-term predictions and long-term projections to foresee the outbreak of snow droughts. This requires strengthening our climate and hydrological modeling and data assimilation capabilities. 

Canada still has abundant freshwater resources. But abundance does not guarantee reliability. Creeping snow drought is a reminder that climate risks do not always arrive as sudden crises. Sometimes they emerge gradually and creep one winter at a time.

Ali Nazemi is an associate professor in the Department of Building, Civil, and Environmental Engineering at Concordia University in Montreal. 

© National Observer