Caution: wild weather ahead

The characteristics of prairie rainfall have changed.

Researchers agree that one-day rains have given way to multiple-day events, and storms are larger.

However, total precipitation seems to have stayed the same.

John Pomeroy, Canada research chair in water resources and climate change at the University of Saskatchewan’s Centre for Hydrology, said there are no real trends in total precipitation on the Prairies, but rain has replaced snowfall in spring and fall.

The work that he and others did in the Smith Creek Research Basin of east-central Saskatchewan found that annual precipitation did not change between 1942 and 2014, but there was significantly more rain than snow.

They found increasing amounts of rain in March, May, June and October and a 50 percent increase in the number of multiple day storms.

David Phillips, Environment Canada’s senior climatologist, said people believe more rain is falling, but it’s difficult to measure because of these changes.

He said temperature is easy to measure because it has used the same instrument for centuries and is measured every day.

“Precipitation is a little bit more elusive,” he said.

“It really is just a tin can that sits on the ground. The wind can blow away the drops and it can evaporate. Snow is even more elusive. We’re one of the snowiest countries, but all we do is stick a ruler in the ground.”

Global weather seems to be wetter, he added, but no trends are noticeable in specific areas.

For example, the average precipitation in Calgary from April to September was 364 millimetres in the 1950s and 366 mm in the 1990s, although it dropped to as low as 307 mm in between.

Putting all the weather station data together from a broad geographic area could result in a generalized statement that Canada is a wetter country now than 50 years ago, Phillips said.

“But it’s more evident on the coasts and to some degree in Central Canada, but not on the Prairies,” he said.

Extreme rainfall is the other factor, which various places on the Prairies have experienced, particularly in the last five years.

Phillips said extremes are usually localized, and it’s difficult to obtain good statistics on exactly how much rain has fallen.

Large rainstorms can cause havoc, such as the one in Maple Creek, Sask., in 2010 and the Calgary flood of 2013.

“The big storms upstream of Calgary and in eastern Saskatchewan were part of trends for larger and longer rainstorms in the Prairies,” said Pomeroy.

“This is climate change producing the change in rainstorms, so one may indirectly associate these events with climate change.”

Phillips said a warming world means the atmosphere holds more moisture. The conditions to trigger that moisture don’t always exist on the Prairies, but they do in more humid areas.

Prairie residents have been surprised by the extreme rain of the past few years, but they might want to prepare for more of them.

A study that Pomeroy and student Kevin Shook did in 2011 examined the Historical Adjusted Climate Database for Canada to determine the fraction of monthly precipitation that fell as rain on the Prairies. They looked at 1901 to 2000 as well as the shorter period of 1951 to 2000.

“Over the period 1951 to 2000, the fraction of summer rain falling as single-day events has been decreasing at many locations (one site showed a significant increasing trend and many showed no trend),” they wrote in their published research.

“Significant decreasing trends were also found at the majority of sites over 1901 to 2000.”

However, they also found that summer multiple-day rains had significantly in-creased at many locations over the periods that were analyzed.

Phillips said prairie farmers aren’t really set up to deal with such weather variability. For example, 43 mm of rain fell in Regina this past spring compared to 310 mm the previous year.

“In 10 months, parts of Saskatchewan went from the wettest to the driest conditions in history,” he said.

Weather patterns are destabilizing, and he expects more of the same. He said even if precipitation increases, the effect could be less because of warmer temperatures.

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