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Scientists link November 2021 Floods to Human Influence

An attribution analysis of the atmospheric river event that struck southern BC on November 14th and 15th of 2021, conducted by a team of scientists from PCIC and Environment and Climate Change Canada, has recently been posted on the SSRN preprint server. Atmospheric rivers, which are long, thin bands of moisture in the atmosphere, are characterized by their magnitude, meaning the amount of water vapour that they transport. The researchers found that atmospheric rivers of the magnitude of the November event can be expected to occur, on average, once every ten years in the current climate of the region. They also found that such events are at least 60% more likely due to the human influence on the climate system. In terms of the amount of precipitation that fell over those two days, the researchers found that the event was about a one in 50-to-100 year event and they estimate that the probability of such events has increased by about 50% due to human-induced climate change. The team also found that the effect of the intense precipitation on river streamflow was made worse by existing wet conditions in the region prior to the atmospheric river, and by snowmelt at higher elevations. These came together to form a compound extreme event, leading to maximum values of extreme streamflow that exceeded 1-in-100 year values at several basins in the region. The authors estimated that the probability of such extreme streamflow events are two to four times as large as they were in the 1950s, as a result of human-induced climate change.

Read the press release from UVic News.

Read the research paper.

Watch a recorded talk on this paper, as part of the Pacific Climate Seminar Series.

(This page was updated on 2022-05-13 to reflect the publishing of the research paper.)