Published July 6, 2014
Smith Creek in southeastern Saskatchewan normally runs dry in July. Last week it hit an all-time 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,” says John Pomeroy, director of the centre for hydrology at the University of Saskatchewan. 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, says Pomeroy. 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 a billion dollars as farmers lose crops and communities mop up. The flood comes just weeks after waters rose in southern Alberta, flooding several communities there, and just a year after flood waters tore through Calgary causing what’s 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 funneling 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 sloughs 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 eastern North American 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 than are over in minutes, not rains that last for days, says Pomeroy. Prairie floods have historically been caused by spring snowmelt, not summer rain. But in the last decade there has been a marked shift to “rain-derived floods.”
“And this one is blowing all the others out of the ballpark,” says Pomeroy. 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, says Pomeroy, 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 U.S., stalled over southeast Saskatchewan in late June, “and pushed it over the top,” says Pomeroy. 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 last 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 mid-summer. Never.”
The situation calls out for a national Canadian strategy and program to improve flood prediction and water management, says Pomeroy, 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.”
Human hand seen in Prairie floods
Rain is driving the historic summer flood on the Prairies, but there is also evidence of human hands in the swollen water pouring down the Assiniboine River.
The extensive network of ditches that farmers have carved in their land over the years to drain sloughs has significantly increased flood risks on the prairies, according to a recent report by the hydrology centre at the University of Saskatchewan. “Wetland drainage is a major factor in increasing prairie stream flows and increasing flooding,” says the report.
Thousands if not millions of sloughs once dotted the Prairies and stored massive amounts of water in the depressions left when glaciers retreated at the end of the last ice age. It’s estimated 70 per cent of the wetlands have been lost, often drained by ditches that give water a way to quickly escape into creeks and streams and add to downstream flow.
The report focuses on the Smith Creek Basin, an agricultural area covering almost 400 square kilometers in southwest Saskatchewan.
To get a read on the water movement, the researchers installed water gauges, weather stations and used instruments mounted on aircraft to track water as it drops as rain or snow, sinks into the ground, evaporates or flows down Smith Creek. Records dating back to 1958 show wetlands used to cover 24 per cent of the basin but shrank to 11 per cent as farmers dug more and more ditches.
The team led by John Pomeroy then created a computer model to assess how different drainage scenarios – from full restoration of the wetlands to complete destruction – impact stream flows and flooding. The results are dramatic. Wetland drainage since 1958 has increased the yearly stream flow volumes by 29 per cent and increased the peak of a flood in 2011 by 32 per cent, the report says.
It says things could get much worse if the ditch digging continues – the study found complete drainage of existing wetlands would have increased the 2011 flood peak by 78 per cent.
While the scientists have not had a chance to study this year’s flood, drainage ditches have likely contributed to the deluge as they give water a direct way to run into creeks and rivers.
Scientists say stepping up programs to restore and conserve wetlands could go a long ways towards helping reduce future flood risks. “It would provide tremendous service, and it’s a lot cheaper than building dams,” says Pomeroy, director of the centre for hydrology at the University of Saskatchewan.
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