If you think Victoria has been subjected to an unusually high level of rainfall this winter, you’re mistaken.
The actual measured precipitation is slightly below average for the October 2015 to mid-March period, but several high intensity episodes of precipitation managed to flood basements and otherwise overwhelm storm water run-off systems.
“It’s due to something called atmospheric river events,” said University of Victoria Associate Professor David Atkinson. He said that veritable rivers of atmospheric moisture are picked up over the equator due to the high energy (of sunshine) over those regions. This prompts the storage of very moist air, which, if drawn toward the North American landmass by a combination of strong pressure systems, has the effect of causing substantial, prolonged rainfall events.
“I have one colleague who likens it to turning a fire hose on the West Coast,” said Atkinson.
According to Atkinson, another reason for the high intensity rainstorms this year has been the shifting of pressure systems along the coast, which has drawn storm moisture in from pressure systems formed over the ocean.
“We generally get the remnants of storms that form around Alaska. That results in lower intensity rainfall events of longer duration,” he said. “But this year we’ve seen storm systems move in from the Pacific and even down the California coast.”
Victoria’s 705 mm of annual rainfall is about half of what Vancouver receives every year.