Flood incidents likely to grow

Forecast models take into account climate change and housing developments

Alberta should brace itself for more flooding if scientific models are correct.

Eighty percent of the water in the Bow River is from snow melt originating in the Rocky Mountains.

Research shows water yield as down between 1971 and 2004, but the province has experienced serious and costly floods since 2005 that overwhelmed local infrastructure, said University of Calgary researcher Sandra Ungerson.

Some of the floods have been caused by “scary rain events,” she told the Bow River Basin Council’s science forum April 15 in Calgary.

Sudden bursts of high rainfall are happening around the world and are linked to an atmospheric river located south of the jet stream that transports water vapour around the world. It can be responsible for huge dumps of rain under the right conditions.

Up to half of the rain in western North America comes from this river, she said.

“We can’t anticipate who is going to get drowned and who is going to get missed,” she said.

The $5 billion flood of 2013 was the result of rapid snow melt and a deluge of rain in a short period, said Babak Farjad of the U of C.

Part of his research is modelling future scenarios to make flood damage predictions up to 2066 based on past events going back to 1985.

Climate change, increased population and regional development all affect the watershed, and Farjad predicts the region will be more vulnerable to floods than drought.

The models consider water storage, vegetation, groundwater and surface water. From there, five temperature and precipitation scenarios are projected. Most of the models show that high stream flows could be earlier in spring with higher peak flows.

However, a reduction in annual overland flow and groundwater recharge is more likely in most years.

There could be more evapo-transpiration, which also affects the infiltration of water into the ground.

Jason Abboud of the U of C has found that the greatest household damage from the 2013 flood was from groundwater flooding.

He interviewed hundreds of home-owners, and many reported the surge of flood water came up through floor drains, toilets, sinks and cracks in the foundation.

Flood damages eventually cost more than $5 billion. Less than $2 billion was insurable damage.

Damage to a basement flooded by groundwater was estimated at $96,000, while a combination of groundwater and surface water inundation cost $240,000.

Abboud said more groundwater monitoring wells are needed to provide an early warning of approaching flooding.

“These could be relatively inexpensive,” he said.

  • Thirty to 50 percent of annual precipitation in the West occurs in just a few atmospheric river events, thus contributing to the water supply.
  • The strongest of these rivers can create major flooding when they make landfall and stall over an area.
  • They are a primary feature in the global water cycle and are tied closely to water supply and flood risks, particularly in western North America.
  • The Pineapple Express, which brings moisture from the tropics near Hawaii to the U.S. West Coast, is a well-known example of a strong atmospheric river.
  • A strong atmospheric river transports an amount of water vapour roughly equivalent to 7.5 to 15 times the average flow of liquid water at the mouth of the Mississippi River.
  • These rivers are 400 to 600 kilometres wide and are present somewhere on Earth at any given time.
  • Improved understanding of atmospheric rivers and their importance has come from a decade of scientific studies using new satellite, radar and aircraft observations and major numerical weather model improvements.

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