Rain-soaked Prairies victim of ‘regime change’
‘Unprecedented’ flooding part of ‘regime shift’ bringing huge rains
Smith Creek in southeastern Saskatchewan normally runs dry in July. Last week it hit a record high and the stream gauge that scientists have been monitoring for decades is now under water.
So are countless homes and farms in Saskatchewan and Manitoba, where the province has declared a state of emergency and called in the military to help deal with the stunning summer flood.
“It’s utterly unprecedented,” John Pomeroy, director of the centre for hydrology at the University of Saskatchewan, says.
While as horrified as anyone by the flooding, he is perhaps not quite as surprised.
It fits with a “regime shift” in the climate system that is bringing more prolonged summer storms to the Prairies, Pomeroy says.
Combine that with what he describes as Canada’s woeful flood forecasting and management systems and the result is costly disaster.
It is too early to tally the damage of the flood unfolding in Saskatchewan and Manitoba, but the cost is expected to be well over $1 billion as farmers lose crops and communities mop up.
The flood comes just weeks after waters rose in southern Alberta, flooding several communities, and just a year after flood waters tore through Calgary causing what has been described as the country’s costliest natural disaster, with more than $6 billion in damage.
Pomeroy, who holds a Canada research chair in water resources and climate change, says all three unusual floods were caused by moisture-laden storm fronts that moved up from the U.S. and then “stalled.” Rain dropped over large areas for days, saturating soil and funnelling water into streams and rivers, which then overflowed inundating fields, washing away roads and flooding communities. Making matters worse, he says, is the extensive network of ditches farmers have carved out of their land over the years to drain slews and wetlands, which enable water to runs off fields more quickly.
Pomeroy says the increase in stalled summer storms “that just sit there” appears to be tied to a shift in the jet stream and atmospheric flows. The same phenomenon may be responsible for much of the extreme weather seen around the globe — such as the prolonged deep freeze in much of central North America last winter, Australia’s heat waves and the heavy rains than inundated Britain earlier this year.
Normally the Prairies have plenty of short sporadic summer thunderstorms that are over in minutes, not rains that last for days, Pomeroy says. Prairie floods historically have been caused by spring snowmelt, not summer rain.
But in the past decade there has been a marked shift to “rain-derived floods.”
“And this one is blowing all the others out of the ballpark,” Pomeroy says. His team has been documenting the change as part of a research program in the Smith Creek Basin in southeast Saskatchewan, which flows into the Assiniboine River now causing so much misery.
Streams and creeks in east Saskatchewan normally start flowing in March, peak in April and go dry by early May when the snowmelt is done, Pomeroy says, pointing to records that go back to the 1950s. By July, Smith Creek is usually “bone dry.” Last week it hit a new high as 24.5 cubic metres of water a second roared down the stream.
He says heavy winter snow had saturated the soil, which was made even wetter by unusually heavy spring rains. Then the frontal system came up from the U.S., stalled over southeast Saskatchewan in late June, “and pushed it over the top.” The system dropped more than 150 millimetres of rain in a few days — almost as much rain as normally falls in dry southeast Saskatchewan all year.
He says the change in the past decade has been remarkable.
“Everything we know about hydrology on the prairie appears to be different,” he says. “We never have saturated spongy soils with flow running off farmers’ fields in the midsummer. Never.”
The situation calls out for a national Canadian strategy and program to improve flood prediction and water management, Pomeroy says, pointing to the U.S. which has more comprehensive systems.
He says recent cutbacks and, in some cases, the “gutting” of federal hydrology, climate and flood management programs have left the country ill-prepared.
When it comes to the flood-forecasting problem, he says, “every province is left on its own, with some doing better than others.”