Devastating recent floods in British Columbia

Record rainfall caused by atmospheric rivers hit southern British Columbia (BC) in late November 2021, leading to flooding and mudslides as rivers and streams overflowed, damaging farms and homes, and washing away roads, bridges and railways. We examine in this article the meteorological driver of this disaster, its social and financial costs, and what lies in the future.

What are atmospheric rivers?

“Atmospheric rivers” are large, narrow streams of water vapour that travel through the sky. They usually start from warm and moist tropical ocean regions near the equator. In the case of the BC floods, the powerful moisture-laden rivers moved to the mountainous BC coast, and the water vapour condensed into precipitation that resulted in record rainfall.

A devastating flood

The flood event was catastrophic, in both human and financial terms. At the peak of the flood emergency, almost 15,000 people were evacuated from their homes. There were 4 fatalities from the highway mudslides due to the flooding. Dikes were not able to hold the flood water back in the Sumas Valley, a low-lying prime farming area in the province. Many farms and homes were destroyed, and the death toll among livestock included more than 600,000 poultry, 12,000 hogs, 420 dairy cattle and 120 beehives. Many farmers lost not only their homes, but their livelihoods as well, and face a long and expensive road to recovery.

The Insurance Bureau of Canada estimates the insured damage due to the flooding to be $450 million (Canadian), and calls it the “most costly severe weather event in the province’s history”. The overall costs are expected to be much higher as only a fraction of the total damage is covered by flood insurance. A senior economist at the Bank of Montreal noted the total cost of the BC floods could be comparable to the 2013 flood in Calgary, Alberta, estimated at $7.5 billion. In both cases, the costs are shared by insurers, individuals, private companies, taxpayers, and municipal, provincial and federal governments.

What about the future?

Climate science shows we will see more precipitation extremes as long as global warming continues. We will also continue to experience their costly impacts.

CBC News reported on a recent study by climate scientists at Environment and Climate Change Canada, which shows the increase in frequency and intensity of regional heavy rainfall in North America is largely due to global warming. Moreover, we will experience further increases in these extremes as warming continues. Storms that would happen once every 100 years in a climate without human influence now happen every 20 years due to global warming. If the warming continues to reach 2^oC above pre-industrial temperatures, those storms would happen once every 5 years.

Precipitation extremes are a major cause of flooding. We are already experiencing the large social and financial impacts of flooding events. These impacts are caused not by heavy rainfall alone; other factors, such as past land use change that increase our exposure to flooding, and dikes that fail to retain flood waters are also important. The need to reduce greenhouse gas emissions and to increase our resilience through adaptation, has never been more urgent.