BOW VALLEY – For most residents living in the Bow Valley the biggest threat to their way of life is flooding or wildfire, however as climate change begins to take hold water scarcity will likely become a major concern.
Research by David Sauchyn, director of the Prairies Adaptation Research Collaborative, shows the annual flow rate in the Bow River and many other rivers in the Canadian Rockies are in decline, as glaciers recede and the snowpack melts at higher elevation during the summer months.
As a result, communities along the Bow River will likely face water shortages and even drought in the not too distant future.
“We’ve looked at water levels over a period of a thousands years, 900 years in the past and 100 years into the future, and it’s pretty clear there’s a long-term decline of the average water level in the Bow River,” said Sauchyn.
To conduct his research his team used water records and analyzed tree rings on the eastern slopes of the Canadian Rockies to get a better understanding of historic water levels in the river.
“There is a pretty good relationship between the rate of tree growth each year and how much water is available not just for trees, but also for the river, so we’ve been able to determine how much water was available in the river for the last 900 years,” said Sauchyn.
Using the data they gathered, his team was able to determine that the Bow River has been gradually declining for the past 100 years, largely because of the loss of ice on the Bow Glacier and other glaciers in the watershed.
“It’s not just the ice, it’s also the snow,” said Sauchyn. “Historically people’s image of the Rocky Mountains is you go there in the summer time on vacation and you see these snowcapped peaks, well the snowcaps are disappearing. The run off is shifting to earlier in the year and as a result by the time you get to summer that run off, which historically was occurring, is done.”
Backing up his research, last week officials with the City of Calgary revealed the city could reach its daily water withdrawal limit from the Bow and Elbow rivers by 2036 thanks to population growth and climate change.
In Canmore the situation isn’t as dire, however in 2016 the Town of Canmore identified a water supply shortage as a medium risk priority in its Climate Change Adaptation and Resilience Plan.
According to Andreas Comeau, the Town’s manager of public works, Canmore is currently using just over 50 per cent of its daily withdrawal limit and hasn’t done any projections when it will reach its limit.
Regardless, the Town’s climate change adaptation plan acknowledges that reoccurring water supply shortages could lead to water restrictions, have repercussions for the economy and hurt recreational activities.
To mitigate the risk, the plan sets out seven actions, including developing a water shortage response plan in conjunction with EPCOR, which manages the Town’s water supply.
“The idea of water scarcity is definitely something we need to think about,” said Lori Rissling Wynn, the Town’s sustainability coordinator.
“I don’t think we’re quite there yet in terms of urgency like other municipalities, but it would be foolish to think that wouldn’t be part of our future reality.”
To date, she said the Town hasn’t done a lot of work on the plan because it has been focusing most of its energy on mitigating the risk of steep creek flooding and wildfire prevention.
While that might be prudent in the short-term, in the long-term drought mitigation will become more and more important, according to Sauchyn.
According to the Town’s adaption and resiliency plan, between 1985 and 2005 glaciers in Alberta lost approximately 25 per cent of their area and projections estimate glaciers in the Canadian Rockies will lose another 50 per cent of their area by the middle of the century.
Compounding matters, research projects that winter and spring warming combined with reduced snowfall in the winter months will affect the snowpack in the Rocky Mountains.
In fact, in the Bow Valley corridor the average daily snow depth at 1,600 metres is projected to decline by up to 50 per cent by the middle of the century, although smaller declines are projected for higher elevations.
All of this is expected to have a major impact on rivers and streams.
According to the Town’s plan, the flow rate for rivers and streams is projected to increase in the winter, peak earlier in the spring, and decrease in the summer. Melt water from glacial sources will also become increasingly less reliable in the future as glaciers in the eastern Rockies continue to melt.
Sauchyn said communities living along the river haven’t directly felt the impact of river’s decline because water use has dropped significantly over the past few decades thanks to water efficiency programs, better infrastructure and a change in behaviour.
“We simply use a lot less water than we use to per person and as a result that gradual decline hasn’t been a problem, at least it hasn’t been our biggest problem,” said Sauchyn.
He said the bigger problem communities such as Banff and Canmore will face are extreme water levels like flooding and drought.
“What our tree ring studies have taught us is that there are these cycles in the water levels that will last a decade or two, so we’ll get a decade or two of high water levels and then a decade or two of low water levels back at least 900 years and probably much further than that,” said Sauchyn.
“What that means is that you can get several floods within a period of 10 or 15 or 20 years and a much higher likelihood of low water levels and drought for the next 10 or 20 years. In other words, the high water levels will group together and then the low water levels will group together – these events are not random in time.”
He said the general public often misunderstands the notion that a flood of a specific magnitude happens only once every 50 years.
“People have this false perception that a 50 year flood means one every 50 years. It just means over a very long period of time it averages out to one every 50 years, but those tend to group together.”
He said it appears the Bow watershed has recently been though a period of relatively high water levels and is now entering a period of lower water levels.
“In the past there had been long periods of water deficits like the 1930s and prior to the that in the tree rings there are periods of a decade or two in which the river fell and the river was low for a long period of time and that’s going to happen again in the future, but when it does it will happen in a warmer climate.”
He said when that happens climate change will compound the length and severity of the drought, which could impact millions of people across the prairies.
“We’ve looked at all the rivers flowing out of the Rockies because that’s the water supply for most of the people in Alberta and Saskatchewan and even some people in Manitoba and we see a similar partner in all the rivers,” said Sauchyn.
While the Bow River’s flow rate is expected to continue to decline as glaciers and the snowpack recedes, Sauchyn said it won’t entirely disappear.
“There will always be rain and snow, so that decline in the near future is probably going to level off, but the more serious problem is that a warming climate will amplify the hydrological cycle,” said Sauchyn, explaining that will lead to more severe rain storms and longer periods of drought.
To avoid catastrophic events caused by climate change, he said communities will need to begin implementing both flood mitigation and drought mitigation.
“What it’s really going to take is a regional approach to ensure that there is a rationale and efficient use of the water,” said Sauchyn. “The capacity is there, so I’m fairly optimistic that there will be policies, infrastructure and practices in place to make the best use of the water.”
