INUVIK
The effects of climate change are becoming obvious in the Mackenzie Delta's spring breakup season, says a researcher.

Dr. Lance Lesack spoke to an audience at the Aurora Research Institute May 15 about changes in the spring breakup season. - Shawn Giilck/NNSL photo

Dr. Lance Lesack of Simon Fraser University spoke to a full house at the Aurora Research Institute over the lunch hour May 15 about his findings, which suggest the spring breakup season is arriving an average of one week earlier than what has been the tradition.

The Delta has been his primary study area since the early 1990s. He's studied the river ice, biology and diversity of the Delta during that time. "We're at the point now where we can look at some of the changes in the Delta," Lesack said. "We're interested in the increasing hydrological cycle." That's the term for increases in the discharge of Arctic rivers at the same time as they are undergoing earlier spring breakups.

Data on large rivers in Russia collected since the 1940s clearly show this increasingly fast hydrological cycle, Lesack said, but not much similar work has been done in Canada's North, and what has been done shows results that doesn't quite fit the theory.

"It all fits with this theory of the increasing hydrological cycle but the interesting thing and the monkey wrench in the system is that the Mackenzie River didn't fit the pattern. We have been getting earlier ice-breakups but the Mackenzie discharges haven't been increasing in the same period as the Russian. We were quite puzzled by this.

"Peak water levels are now occurring earlier than ever in Inuvik," he said. "Historically peak water levels were occurring on June 5, but are now occurring on May 25, so that's eight days earlier."

At the same time, there is no similar trend in Tsiigehtchic. That indicates breakup is occurring faster in a shorter period in the northern sections of the river.

"In the context of that amount of time, that's pretty significant," Lesack said.

"We looked at it in so many ways, but couldn't find any increase in the discharge. We just couldn't see any relationship in the timing of the breakup to the amount of water flowing in the river."

One possibility is that the ice on the river and in the Delta is thinner than it historically had been due to warmer temperatures, so researchers like Lesack started looking at the effect of temperature on the hydrological cycle.

"That's what was driving our thinking," he said. "We were fortunate to have a really great database of temperatures, and we found something interesting was going on.

"The mean winter temperatures from 1958 to 2012 have warmed five degrees," he said. "I don't know if you knew that, but I didn't know that."

The mean winter temperature has gone to -21.2 C from -26.8 C for the winter period, he said. While that's quite considerable, it accounted for only 11 per cent of the variations in peak water levels. The true culprit was found in another season.

During the spring breakup, the temperature has gone to -1.5 C from an average of -7 C, Lesack said.

"Spring temperatures explained more than 80 per cent of the variations in peak water levels. That's a huge effect. It took us a decade to figure this out. It worked big-time, but we were really puzzled about why it worked."

He and other researchers next looked at snow depths and snow pack during the same period and found a significant decline.

"Snow depth has actually declined by about one-third in this time period," Lesack said. "It's a huge effect. That, in combination with warming spring temperatures, is what is driving this really strong response.

"What we can draw from this is that it's a combination of warmer springs and decline in snow depth that's the reason for this. With less snow to melt, it speeds things up."

That's important since, during the spring, the Delta overflows with fresh and semi-fresh water when the spring melt is blocked by ice jams and ridges of sea ice at the mouth of the river. This forms what is known as "Lake Mackenzie" until the ice bursts enough to release the impounded water, Lesack explained.

That "recharges" many of the 45,000 productive lakes in the Delta, contributing greatly to their productivity, and soaks up some of the excess water.

With a more rapid break-up season, less of that is likely going to happen and the Delta may not have the conditions necessary to absorb as much of the runoff and high water, which would make it flow more directly to the Beaufort Sea.

That's likely to have implications on the decline of sea ice and the rising sea levels that aren't well understood at this point, Lesack said.

Changes in the ecology of the Delta are likely to become more noticeable as well without the annual recharge of water. Several people in the audience said they had been noticing similar signs.

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