The Pacific Decadal Oscillation is still being studied, but high water events in the Rockies offer clues

Medicine Lake has breached its banks for the fourth year in a row and a river scientist from the University of Lethbridge is suggesting the occurrence has not as much to do with climate change—although a progressively warming climate is a factor—as it has to do with a reoccurring, less-understood phenomenon called the Pacific Decadal Oscillation. 

The Pacific Decadal Oscillation (PDO) relates to the surface temperature of the Pacific Ocean, says professor Stewart Rood, the author of Declining summer flows of Rocky Mountain rivers: Changing seasonal hydrology and probable impacts on floodplain forests.  

“When you have warm water off Vancouver Island, the Rockies tend to be warmer and drier,” Rood said. 

The PDO was first noted as corresponding to salmon catches, since it changes fish behaviour along Canada’s west coast, Rood said. It has since shown up in reconstructed hydrology cycles in watersheds like the Athabasca River. Scientists have data going back more than a century on the Athabasca—it’s the oldest, most continuous hydro station for any North American river flowing to the Arctic Ocean—so they can look back for high water/flood history, among other events. Searching those models for patterns, “the strongest signal is the correlation with the PDO,” Rood said.

Meanwhile, when Medicine Lake spills over, the signal goes up in kayak circles that “Excalibur,” a class five rapid that appears only when the high-water event occurs, is coming into shape. As the water rises over the lake’s rim, it flows into the steep gradient adjacent to the basin. If there is enough water volume, the ravine soon hosts a foaming, frothing torrent which, in July in Jasper National Park, hurtles itself past about 1,000 tourists per day on the Maligne Lake Road. 

This year, the overflow started on July 4. A few days later, as water surged over and around the canyon’s huge boulders, long-time Jasper paddler Shawn Allen scouted for an improbable line through the swelling surf, next to razor sharp rocks, around a twisting, gushing, frenzy of whitewater and roots and into a small eddy.

“You have to watch out you don’t get caught in that big hole,” Allen said, pointing into a boiling, gurgling void. “Not many people have run it twice.”

In fact, not many people have run it at all. Rood, himself a paddler who boated with the Alberta kayak team in the 1990s, said he wouldn’t have toyed with the drop, even in his prime. 

“It’s just so big and so fierce,” he said. 

And now, thanks to the Excelsior Creek wildfire which burned there in 2015, Excalibur is even more fierce than in the past. In the seven years since the 1,000 hectare fire burned, charcoal-black trees have been laid down by wind and snow, creating snarl upon snarl of jagged, towering deadfall. Because of all the wood, the run is considered unnavigable. Allen, who remembers reading about the mythical rapid in a dog-eared copy of Stuart Smith’s guidebook, Canadian Rockies Whitewater, got his chance to run Excalibur in 2012. Smith is a paddler and author who called Jasper home for many years. He pioneered the run in 1992.

“He probably would have done it in a fibreglass boat,” Allen said. “That’s would be unheard of for paddlers today.”

Most paddlers—most people, for that matter—likely wouldn’t have heard of the Pacific Decadal Oscillation, either. But it is Rood’s hypothesis that this phenomenon is contributing to the more-consistent overflowing of Medicine Lake, among other wet-dry cycles in the Rockies. Prior to 2019, the last time Medicine Lake breached its banks was in 2012—the same summer that kayakers last boated there. Before that instance, Medicine Lake was recorded as overflowing in 2002, 1992, and 1990. Jasper naturalist Volker Schelhas, who along with his partner, Paulette Trottier, lives at the Maligne Canyon Wilderness Hostel (appx 10 kms from Medicine Lake). Schelhas has kept meticulous records on a wide range of ecological occurrences in the area including bird migrations, snow levels, wildlife sightings, turning leaves and unusually-high lake levels. 

“It’s the most frequent we’ve ever seen,” Trottier said of Medicine Lake’s four-years-running overflow. 

Rood was delighted that Schelhas and Trottier are keeping track of area water levels. There hasn’t been a formal gauge in the Maligne system since 1979. If the Water Survey of Canada still maintained a hydrometric station on the Maligne River, river scientists of the future could potentially look back at the precise discharge data of the Maligne system and be able to correspond the overflows with the patterns of the PDO, Rood said. As it stands, the gauge on the Athabasca will have to suffice. Moreover, the PDO is still being understood.

“Climatologists don’t understand what drives the swirling of the massive, warm pools in the Pacific,” Rood said.

They’re working on it, but it’s a difficult phenomenon to grasp because the analyses are retrospective, rather than predictive. Hydrologists can see that the droughts in the 1930s were associated with the PDO, as were the droughts in the 1980s, but predicting these occurrences into the future is more difficult. A progressively warming climate has certainly accelerated glacial recession and there are weather events such as rain and fire which will affect the rate of snow melt in a particular catch basin, but Rood is more interested in looking at the syncopated cadence of the PDO to explain why the high water events took place once every 10 years, and then occur in a cluster of four years in a row, for example.

“What I would hypothesize is that part of the variations, and especially the clusters of years in which Medicine Lake is higher and overflows, may well correspond with a particular phase of the PDO.” 

That’s all fine for Allen, who knows that unless the deadfall somehow becomes dislodged from the Medicine Lake outflow, Excalibur will probably remain unnavigable. And it’s probably more than enough information for the average visitor to Jasper National Park, who might click a few photos of the spillover phenomenon en route to a boat cruise on Maligne Lake. But for river scientists such as Rood, unlocking clues to the Rockies’ river systems opens up the potential to understand the bigger, more relevant picture: water scarcity. If anything could come out of gawking at 2022 Medicine Lake overflow—because it won’t be videos of extreme kayaking down Excalibur—Rood thinks that the hydrometric station on the Maligne River should be re-established.

“My view is that while global warming is a big deal, the impact of climate change on water is a bigger deal. We really need to have these data to understand mountain hydrology.”

Bob Covey // bob@thejasperlocal.com