Atmospheric rivers can cause havoc for communities and the economy

It rained throughout yesterday's Chinese New Year parade in Vancouver. And today, there will be more wet weather across the Lower Mainland.

This morning, five to 10 millimetres of rain is expected. Then there will be another 10 to 15 millimetres in the afternoon, followed by a similar amount in the evening.

Vancouver averages 111 millimetres of precipitation in February, which means the city could receive more than a third of that in a single day. Temperatures are expected to hover around 8 °C.

As Vancouver is about to experience intense rainfall, it's worth paying attention to a new book called Storm Warning: Water and Climate Security in a Changing World (Rocky Mountain Books). That's because it offers deep insights into why Canada has experienced unusual rainfall patterns in recent years.

Written by Alberta-based water expert Robert William Sandford, Storm Warning points out how climate change is transforming hydrological cycles. A warmer atmosphere carries more water vapour, increasing the likelihood of more intense storms.

In the book, Sandford also highlights how scientists are learning more about massive "atmospheric rivers" that dump enormous amounts of rain.

These "corridors of intense winds and moist air" can be thousands of kilometres in length and extend for 400 to 500 kilometres across.

According to Sandford, atmospheric rivers may "carry the equivalent of 10 times the daily discharge of the St. Lawrence River".

"We have discovered recently that atmospheric rivers derive their energy from the temperature gradient between the poles and the tropics," Sandford writes. "Their intensity also derives from the Clausius-Clapeyron relation in that the warmer the air, the more water atmospheric rivers can carry."

He reports that in 2013, one of these atmospheric rivers dumped a record amount of rainfall in the Kootenay-Columbia River region.

The same year, Canada's largest natural disaster occurred in Alberta as intense rainfall caused a massive flood in Calgary, High River, and other communities. More than 100,000 people were evacuated from their homes and Calgary's central business district was shut down.

Two weeks later, Sandford notes in his book, a sudden rainstorm in Toronto caused more than a billion dollars in insured losses. It also flooded parts of the subway system. 

In the same year, Russia and Colorado experienced devastating floods that were completely out of the norm.

"Taking Colorado's experience together with Alberta's and Ontario's, we might surmise that the floods of 2013 offer us a glimpse into the highly variable weather we might expect in a warming world," Sandford writes. "These events certainly got everyone's attention. They clearly demonstrated that our global hydrology is clearly changing."

And this, he suggests, is "undermining the predictability upon which our economy depends for its own stability".