The city of Vancouver, British Columbia, Canada, and its metropolitan areas together have a population of roughly 2.5 million. An atmospheric river of severe rainfall enhanced by global warming has inundated large swaths of the Pacific Northwest region; damage is severe in Vancouver where highways have collapsed, roads and towns covered in mud and rock from landslides in addition to severe erosion destabilizing roads. The damage is devastating in that there is no way for residents or supplies to enter or leave the city by road. Rescuers have begun the grim task of finding people and cars buried by landslides from the record-breaking rainfall and snowmelt caused by the storm.
This is it, folks; there is no doubt we are seeing the impacts from warming earth. Roads, railroads, and ports are closed, supply chains severed, suffering and terror for millions. The event occurred just days after COP26 ended in an underwhelming whimper.
The Royal Canadian Air Force rescued hundreds from the threat of mudslides. Many are trapped in their homes, and returning to normal is months away as winter snow and ice loom. The Trans Mountain Pipeline that transports oil to Canada's west coast has been shut down. A barge torn off its moorings is lodged on the seawall.
Six months ago, British Columbia endured 120-degree temperatures along with raging out-of-control wildfires; 595 people did not survive the onslaught. The town of Lytton incinerated. Today the burn scars have made the flooding that much worse by triggering the slides. Climate change is a threat multiplier.
Jeff Masters writes in Yale Climate Connections.
An atmospheric river (AR) is a band of water vapor 400-600 km wide – like a river in the sky – that acts like a pipe transporting huge amounts of water vapor out of the tropics. The amount of water that a strong atmospheric river can transport is about 7.5-15 times the discharge of the Mississippi River. When an atmospheric river moves over land, the water vapor transported can condense in the form of rain or snow, often causing extreme rainfall and flooding. In the western U.S., atmospheric river events are responsible for most of the region’s flood damages, according to a 2019 study.
In the case of this week’s atmospheric river in western North America, the moisture came from the vicinity of Hawaii, and the atmospheric river pulled moisture from ocean waters up to one degree Celsius (1.8°F) above average in temperature. Atmospheric rivers originating near Hawaii are often called “the Pineapple Express”.
Surface waters of 1.8 degrees F are able to evaporate seven percent more water vapor in saturated air such as this storm.
In Washington State, which received copious amounts of rainfall as well, Jay Inslee has declared a state of emergency. Our cities and towns' infrastructure was not built for this century’s natural disasters; the events are getting bigger and more powerful. Vancouver and Seattle prove how vulnerable we are to serious disruption.
The excellent Climate Signals website, which connects real-time extreme weather events to climate change, has this information on atmospheric rivers and climate change:
- As the climate warms, ARs are expected to form in more rapid succession and grow more intense as they become wetter, longer, and wider. There is some indication that this is already happening in association with observed Pacific Ocean warming.
- An August 2017 study spanning seven-decades of data revealed a rising trend in land-falling atmospheric rivers consistent with a long-term warming of the North Pacific, which sends more water vapor to North America. The study also identified an increase in the amount of moisture that atmospheric storms transport.
- A July 2015 study found that climate change may increase horizontal water vapor transport by up to 40 percent in the North Pacific, due mainly to increases in air moisture.
- ARs in the western US warmed substantially from 1980 to 2016. Warmer storms have important impacts on water resources, such as more precipitation falling as rain instead of snow, causing early snowmelt and flooding.
- ARs distribute heat energy from equatorial regions toward the poles. Climate change is leading to shifts in energy flows, expanding regions of stable, warm and dry air in the subtropics, which shifts atmospheric rivers poleward.
- Huang et al. 2018 found that an unusually warm AR preceded the Oroville Dam crisis and played a major role in the failure of the dam’s spillway. Runoff in the watershed supplying the Oroville dam during the peak precipitation immediately prior to the dam failure was one-third greater than it otherwise would have been, were it not for global warming.
More rain will be coming to the region later this week.
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