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Water from the Athabasca River is crucial for oil sands operations in northern Alberta.Larry MacDougal

If you worked in the fur trade in 1796, Alberta was not the best place to be. Sure, there was plenty of fur around. The problem was how to ship it out.

"Without … a rise of water it will not be possible for us to get down full loaded," wrote William Tomison, the Hudson's Bay Company representative at Edmonton House, in a letter dated May 7. A log entry from the same week reports damage to canoes coming up the North Saskatchewan River. "The river is unaccountably shallow," it reads.

Now a long-term study of the Athabasca River, just to the north, suggests these accounts carry a warning about the future availability of river water for oil sands mining.

Based on a 900-year record obtained from tree rings, researchers found that the Athabasca watershed has historically been subjected to prolonged dry spells that are far more severe than anything the region has experienced since the oil industry arrived there in the 1960s. And with climate change threatening to increase the frequency and severity of droughts, they say, Alberta's oil producers may be relying on an "untenable assumption" that the river's flow today is representative of what they can expect in years to come.

"In most centuries there were times when the water level fell and stayed low for decades," said David Sauchyn, a paleohydrologist at the University of Regina in Saskatchewan and lead author of the study. "If one of these prolonged droughts was to reoccur there would have to be serious water conservation."

The study, published Monday in the Proceedings of the National Academy of Sciences, speaks directly to the ongoing debate over how much water should be diverted for oil extraction, particularly at times of diminished river flow.

Currently, oil sands production consumes less than 5 per cent of the river's annual flow, amounting to 187 million cubic metres in 2012. But water use has been projected to climb to 505 million cubic metres within the next decade.

Regulators can apply cutoffs to industry if it's determined that the river level is too low, but Syncrude and Suncor, the original two companies in the oil sands, are exempt. Both rely on water-intense surface mining to extract bitumen.

The modern record of water flow on the Athabasca River begins in the 20th century. To reach further back, researchers used wood specimens collected along the river basin to assemble a complete water record dating as far back as the year 1111 A.D. The relative width of the growth rings in the wood can be used as a proxy for how much moisture was available to living trees during different years.

The tree ring data reveal that the river has dipped below an average annual flow rate of 200 cubic metres per second at least 36 times over the last nine centuries. That's less than half the modern average and lower than any annual rate since oil production began. It's inevitable that such conditions will reoccur, the authors say, and a warming climate is likely to bring them on sooner rather than later.

Companies operating in the oil sands typically store water at times of higher flow to act as a buffer, but a sufficiently severe and long-running drought would overwhelm such measures. It may also force regulators to weigh the industry's needs against damage to the river's downstream ecosystems.

"This long term analysis really underscores the concerns that people have," said David Schindler, an ecologist with the University of Alberta who has studied the potential impact of low water on fish habitat and reproduction in the Athabasca. When water is low, particularly during the winter months,  there is increased risk that fish eggs will be exposed and that juvenile fish will be trapped when shallows areas freeze over.

The tree ring study was partly funded by Canada's Oil Sands Innovation Alliance (COSIA), an industry-backed co-operative whose mandate includes improving environmental performance.

John Brogly, who directs water-related projects at COSIA, said the industry was looking to achieve a 30-per-cent reduction in water intensity – the amount of water consumed per barrel of oil. "Our members are certainly focused on this," he said.

But Dr. Sauchyn said the positive impact of such a reduction could still be outpaced by the overall growth of the industry, and that water availability was still likely to be a future issue of concern on the Athabasca.

Editor's note: An earlier version of this story incorrectly said 200 cubic metres per second is more than half the modern average annual flow rate of the Athabasca River. It is actually less than half (meaning that historic flows have at times decreased by more than half the modern average).

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