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Climate change made B.C.'s November floods 2 to 4 times more likely

daftandbarmy

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BLUF (literally): “Use these numbers to plan for the future.”


Climate change made B.C.'s November floods 2 to 4 times more likely​


The study also found the atmospheric river that killed five people and forced nearly 15,000 from their homes was made at least 60% more likely because of humanity's influence on the global climate

The record floods that washed out British Columbia’s highway system, killed five people in landslides and flooded several communities was made two to four times more likely because of human-caused climate change, a new study has found.

The research, the latest in an emerging science known as “rapid attribution studies,” brought together a leading group of 14 climate researchers to gauge how climate change influenced the magnitude of the atmospheric river weather event, how much rain it dropped and the rivers that later flooded.

From the air, the kind of atmospheric river that made landfall in B.C. last November was made at least 60 per cent more likely due to human influence on the climate. By the end of the century, the report notes such rainfall events are expected to become twice as frequent.

“Those return periods are going to continually get shorter as climate change proceeds,” said Faron Anslow, a climate scientist at the Pacific Climate Impacts Consortium (PCIC) and one of the study’s authors.

“What we see right now is changing under our feet.”

Atmospheric rivers are made up of long ribbons of water vapour, which regularly funnel warm, subtropical air from lower latitudes to B.C.’s coast in the winter. Moving with the weather, they stretch thousands of kilometres and carry moisture “equivalent to the average flow of water at the mouth of the Mississippi River," according to the U.S. National Oceanic and Atmospheric Administration.

Past studies have found atmospheric rivers are responsible for 90 per cent of extreme rainfall in coastal B.C. While common in places like California, over the last several decades, they have increasingly made landfall in B.C. and Alaska.

In the case of November’s atmospheric river, the rainfall was the main driver of the flooding that rocked many B.C. communities, said Elizaveta Malinina, one of the report's authors and a research scientist at Environment Climate Change Canada’s Centre for Climate Modelling and Analysis.

Under current climatic conditions, such a storm could return every 10 years. That drops to every eight years with 1.5 C of warming, and once every five years if global mean temperatures climb 3 C above pre-industrial levels, something Malinina says could happen by the 2080s.

But the atmospheric river also raised temperatures across the region, melting snowpack and swelling rivers to levels usually only witnessed every 50 to 100 years.

“At the really fine-scale, it was really unprecedented,” said Anslow, who last summer co-authored a rapid attribution study linking the Western North America heat dome to climate change.

The flooding has led to an estimated $450 million in insured damage, making it the most expensive natural disaster in B.C.’s history, according to the Insurance Bureau of Canada. The real financial toll, however, is thought to be much higher, as many flooded residents did not have flood insurance. The province, meanwhile, is expected to be on the hook for billions of dollars more.

Consider the widespread destruction seen in Princeton, the evacuation of the entire town of Merritt, or the flooding of roughly 1,000 homes in the Sumas Prairie region of Abbotsford — each community has its own unique geography and risks, said Malinina.

“Basically, this precipitation over two days was the main driver of the flood,” she said. “But risks for different rivers varies a lot.”

In the Coldwater River near Merritt, for example, the chances of a 100-year flood have spiked over 50 per cent since 1950, while in the Stave River, that risk has climbed only 13 per cent.

As B.C. looks to rebuild, both Anslow and Malinina say those kinds of local differences matter.

“We had to do this study relatively quickly while it’s still important,” said Malinina. “...right now there are workers rebuilding.”

“Use these numbers to plan for the future.”

 

Brad Sallows

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Under current climatic conditions, such a storm could return every 10 years.

OK, so they have a hypothesis and they made a prediction. Now we'll see how it bears out.

The "2 to 4" times thing, going by the abstract, is an estimate based on simulations (models). The uncertainties involved are large. 1 in 50 to 100 years - that's a long range of time. I wouldn't stick policy on that - opportunity cost is an inexorable fact of life.
 

MilEME09

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here is another factor that made it more likely, rapid human expansion, we built Abbotsford in a dry lake bed for goodness sake, whoever thought it wouldn't flood should be shot. This situation was frankly only a matter of time no matter what, and many factors played a role.
 

Brad Sallows

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It isn't that no-one thought it would flood. Everyone always knew that it could flood, and that a sufficient amount of water was possible without new-fangled theories involving "climate change". The problem is that they declined to keep increasing the mitigation measures.
 

Colin Parkinson

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Funny I attended a talk shortly after the event and the experts on these atmospheric rivers said that "There is no evidence currently that this event is due to climate change and proceeded to explain how they form and what level they are classified as. The moderate version have been called the "Pineapple express" due to their origin.
 

Navy_Pete

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Cool story bro. When insurance companies and banks stop working with ocean front property and the worlds elite stop buying it, I’ll start to worry about rising sea levels.
All groups and people who can afford to work elsewhere (or just deny claims in the insurance company case under the 'Act of God' clause). If what rich people are doing dissuades you from looking at facts, I've got some NFTs to sell you.
 

OldTanker

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Full disclosure. Before I retired I ran a consulting company that, amongst other things (mainly emergency preparedness) advised clients on climate change adaptation. We had on our team the previous head of the Canadian Weather Service to provide scientific input and oversight. We never claimed we could make a 100% accurate prediction of the future (anybody who does so is a fool) but we were confident of the trends we had identified. The air was getting warmer over the Pacific. This was measurable and verifiable. The warmer the air got, the more water vapour it could hold. Eventually, all this water vapour had to come down somewhere. It would continue to fall when rain has always fallen, in BC's case, on the western slopes of the Coastal and Rocky Mountains, amongst others. This rainfall would be significantly heavier than in the past and would likely overwhelm our flood and rainfall control measures that had been designed for lower rainfall rates. Our advice to clients was to start implementing adaptation measures immediately (this was 20 years ago) as the heavier precipitation was still some years away. For example, we advised our clients that when they replaced storms sewers as part of regular maintenance, or for any other reason, increase the drainage capacity. Replace a six inch pipe with a 10 inch pipe for example. Doing it this way was relatively inexpensive. Similarly, we urged them to implement zoning restrictions on waterfront development. Again, any sort of warming of the Pacific Ocean would result in sea level rise. This was simple physics and mathematics - warmer water takes up more space, and the only way it can go is up. There were some variables, in particular the fact that much of coastal BC is still "rebounding" following compression caused by the glaciers, but the real unknown was how much of the Antarctic and Greenland ice would melt and add water to the oceans. We went with a simple, "plan for a 3 metre rise in the next 100 years" as a reasonable (at the time) planning figure. So all of this was predicted. Was it perfect, of course not. Did our clients pay attention? Some did, some didn't. You can probably guess who didn't. Did we get it right? Draw your own conclusions. I will tell you that those clients who dismissed our predictions with (what I often read here) "if you can't predict this perfectly, we aren't going to believe you" are now reaping the rewards of those decisions. In BC, rainfall is going to get heavier where it has traditionally fallen, summers are going to be noticeably hotter and drier, hotter and drier summer weather will result in more lightning, thus more interface fires, the glaciers are going to recede, and the sea level is going to rise. You can take that to the bank.
 

QV

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I'm still waiting for the hole in the ozone layer to destroy civilization. Or acid rain...

Nobody is saying the climate won't change. It always has and always will. It's the hysteria around the cult of climate change that is the problem.
 

daftandbarmy

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Full disclosure. Before I retired I ran a consulting company that, amongst other things (mainly emergency preparedness) advised clients on climate change adaptation. We had on our team the previous head of the Canadian Weather Service to provide scientific input and oversight. We never claimed we could make a 100% accurate prediction of the future (anybody who does so is a fool) but we were confident of the trends we had identified. The air was getting warmer over the Pacific. This was measurable and verifiable. The warmer the air got, the more water vapour it could hold. Eventually, all this water vapour had to come down somewhere. It would continue to fall when rain has always fallen, in BC's case, on the western slopes of the Coastal and Rocky Mountains, amongst others. This rainfall would be significantly heavier than in the past and would likely overwhelm our flood and rainfall control measures that had been designed for lower rainfall rates. Our advice to clients was to start implementing adaptation measures immediately (this was 20 years ago) as the heavier precipitation was still some years away. For example, we advised our clients that when they replaced storms sewers as part of regular maintenance, or for any other reason, increase the drainage capacity. Replace a six inch pipe with a 10 inch pipe for example. Doing it this way was relatively inexpensive. Similarly, we urged them to implement zoning restrictions on waterfront development. Again, any sort of warming of the Pacific Ocean would result in sea level rise. This was simple physics and mathematics - warmer water takes up more space, and the only way it can go is up. There were some variables, in particular the fact that much of coastal BC is still "rebounding" following compression caused by the glaciers, but the real unknown was how much of the Antarctic and Greenland ice would melt and add water to the oceans. We went with a simple, "plan for a 3 metre rise in the next 100 years" as a reasonable (at the time) planning figure. So all of this was predicted. Was it perfect, of course not. Did our clients pay attention? Some did, some didn't. You can probably guess who didn't. Did we get it right? Draw your own conclusions. I will tell you that those clients who dismissed our predictions with (what I often read here) "if you can't predict this perfectly, we aren't going to believe you" are now reaping the rewards of those decisions. In BC, rainfall is going to get heavier where it has traditionally fallen, summers are going to be noticeably hotter and drier, hotter and drier summer weather will result in more lightning, thus more interface fires, the glaciers are going to recede, and the sea level is going to rise. You can take that to the bank.

Any idea how they've responded to warnings about getting ready for 'The Big One'?

In many ways, we haven't done much about preparing infrastructure to survive even a moderate earthquake, in the most heavily populated areas of BC, either.
 

OldTanker

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Very few municipalities, or the provincial government, really take emergency preparedness seriously. It's expensive and not a vote-getter. Take a look at the BC Parliament Building as a case in point. Ready to fall in even a minor earthquake. But hey! They have a log splitter.
 

Halifax Tar

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Any idea how they've responded to warnings about getting ready for 'The Big One'?

In many ways, we haven't done much about preparing infrastructure to survive even a moderate earthquake, in the most heavily populated areas of BC, either.

J. L. Granatstein has that very scenario in the opening chapter of his book "Who Killed the Canadian Military".

To sum up, it doesn't go well if you can imagine ;)
 

OldTanker

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No doubt about that, but the effects of climate change are happening right now, an earthquake might not happen for hundreds of years. Regardless, nobody out here takes any of this particularly seriously. Other than those who deal with it for a living.
 

Brad Sallows

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Just want to emphasize this bit (by repetition):

"The warmer the air got, the more water vapour it could hold. Eventually, all this water vapour had to come down somewhere."
 
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