THE ERA OF WEATHER EXTREMES IS UPON US: “Scientists are generally reluctant to attribute single extreme weather events to climate change, but the exceptional events of recent years are shifting opinion,” stated John Clague, Emeritus Professor in Earth Sciences at Simon Fraser University (November 2021)

Note to Reader:

This article by John J Clague, Emeritus Professor at Simon Fraser University, is republished from The Conversation under a Creative Commons license. Read the original article. The article was written within days of the record storm experienced in Southwest British Columbia over the weekend of November 13-14, 2021.  

The Conversation rated Clague’s story as one of 10 great stories from the Environment + Energy section in 2021 to read — or re-read.

John Clague worked as a Research Scientist with the Geological Survey of Canada from 1975 until 1998. In 1998 he accepted a faculty position in Department of Earth Sciences at Simon Fraser University. Clague is a Quaternary geologist with research specializations in glacial geology, geomorphology, natural hazards, and climate change. He is former Director of the Centre for Natural Hazard Research at SFU.

Flood waters cover highway 1 in Abbotsford, B.C., on Nov. 16, 2021.

How an ‘atmospheric river’ drenched British Columbia and led to floods and mudslides

The West Coast of Canada is known for its wet autumn weather, but the storm that British Columbia’s Fraser Valley experienced over the weekend of November 13-14, 2021 was one for the record books.

A weather system called an “atmospheric river” flowed across the southwest corner of the province and, over a period of two days, brought strong winds and near-record amounts of rain, which caused widespread flooding and landslides. So far, one person has died.

Hope, Merritt and Princeton, which were particularly hard hit, received 100-200 millimetres (or more) of rainfall. And all of the highways connecting Vancouver to the rest of the province were closed due to washouts and landslides, isolating the city from the rest of Canada, at least by road, with significant economic impacts.

What is an atmospheric river?

An atmospheric river is a band of warm, moisture-laden air many hundreds of kilometres long and hundreds of kilometres wide that borders a large cyclonic low-pressure system.

The term has been applied to bands of moisture-associated weather systems that move inland from the Pacific Ocean. An atmospheric river can reach the coast anywhere between southeast Alaska and Northern California.

Because of the large amount of moisture conveyed in these weather systems, the term has become a metaphor for a terrestrial river. However, atmospheric rivers are not carried in a channel like a real river and can dump prodigious amounts of rain over large areas.

An infographic showing the flow of condensed water vapour from the ocean onto land.The science behind atmospheric rivers. (NOAA)

Was it a record-breaking rainfall?

The weekend storm was noteworthy for both its duration and its intensity. It rained continuously over much of the storm track for more than 24 hours and the rate was higher than normal autumn rains.

In both cases, rapid runoff exceeded the carrying capacity of streams and rivers, causing them to spill out onto floodplains. In addition, flat areas like the Sumas Prairie area between Abbotsford and Chilliwack had already been saturated with October and early November rainfall, were unable to drain away the water and were consequently flooded.

Furthermore, snow at high elevations melted under the warm rainfall, exacerbating the flooding. Rainfall on Nov. 14 set records for many places in the region. For example, Abbotsford recorded 100 millimetres of rain that day, exceeding the previous record of 49 millimetres set in 1998. Hope had 174 millimetres, five times the amount in the record year of 2018.

Did summer wildfires make the situation worse?

B.C. had its second worst wildfire summer season in 2021, with more than 1,600 fires charring nearly 8,700 square kilometers, mainly in the southern part of the province. Only 2017 saw more forest lands burned.

Soils in forested landscapes are hydrophobic after severe fires — they repel water. Super-heated air during a wildfire disperses waxy compounds found in the uppermost forest litter layer. The compounds coat mineral grains in the underlying soil, making it hydrophobic. The water-repelling layer is typically found at or a few centimetres below the ground surface and is commonly covered by a layer of burned soil or ash.

Many areas burned during the 2021 wildfires, such as around Merritt, were deluged by rain the weekend of Nov. 13. It is possible that runoff from these burned grounds was greater and more rapid because of the hydrophobicity of the soil.

Is this related to climate change?

Scientists are generally reluctant to attribute single extreme weather events to climate change, but the exceptional events of recent years are shifting opinion.

Examples of such exceptional events include flooding in western Germany and eastern Belgium and in Henan Province China, both in July 2021; extreme heat and wildfires in Siberia in 2020 and 2021; and the “heat dome” over western North America at the end of June 2021.

These events are so far “off scale” in comparison to past historic extreme events that climate modellers assert that they would not have happened or would not have been as severe were it not for climate change.

Such events are consistent with predictions made by atmospheric scientists that weather extremes will become more frequent and more severe as Earth’s climate continues to warm.

A row of people holding shovels stand on the edge of a dirt road, surrounded by orange smoke.Volunteers pause as they work to control a wildfire near Kyuyorelayakh village, west of Yakutsk, Russia, in August 2021.
(AP Photo/Ivan Nikiforov)


Adjusting to a Changing Water Cycle in British Columbia: Longer, drier summers & warmer, wetter winters

On the weekend of November 13-14, 2021 the southwest corner of British Columbia was pounded by an epic atmospheric river. Landslides and rampaging rivers severed all highway connections between the Lower Mainland and the Interior of the province.

Barely 48 hours later (on November 17, 2021), the Partnership for Water Sustainability’s Kim Stephens delivered the keynote address at an operator educational event organized by the BC Water & Waste Association (BCWWA). Held in New Westminster, the BCWWA event was distinguished by the fact that it was not a Zoom webinar.

On the contrary, it was the first in-person event for water education in the age of COVID. Thus, it was an ironic twist that Mother Nature prevented speakers and attendees from the Interior from attending. The rippling impact of the natural disaster was further accentuated when some 20 municipal staff from the cities of Abbotsford and Chilliwack were called to duty. It was all hands on deck in those communities after widespread flooding in Sumas Prairie shutdown the Trans Canada Highway.

In summary, the historic storm and flooding was top of mind for all when Kim Stephens, Partnership Executive Director, stepped on stage to provide his career perspective on current events, and put the situation in context.

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Download a copy of the keynote presentation titled Adjusting to Longer and Drier Summers in British Columbia: Drought Affects Us All.

A Career Perspective on Droughts and Floods in British Columbia

“Dating back to the Halloween 1981 Flood, my engineering career has been defined by an alternating cycle of floods and droughts. This four decade history provides me with perspective that in turn allows me to put current events in context,” stated Kim Stephens.

“In water resource engineering, we often talk about the Hydro-illogical CycleThat means – once a decade you have a flood; once a decade you have a drought. You write a report. You put it on the shelf. A decade later, you have a flood, you have a drought, you update the reports. And so the cycle continues. As the hist0ric storm of November 2021 shows, however, no longer can we postpone action that recognizes the nature and reality of a changing water cycle.”

“Droughts affect all of us, whereas floods affect some of us. That is a fundamental distinction. For this reason, drought history is a good way to tell the story of how our climate is changing. In British Columbia, the mega-drought of 1987 was our first wake-up call. It followed a relatively benign period of some four decades. In rapid succession, we had three droughts in five years. This began to change the conversation in British Columbia.”

“Starting in 2003, we have had one teachable year after another in British Columbia. The pattern has been extremes followed by extremes: droughts, forest fires, wind storms, and floods. Each time the extremes seem to be more extreme. 2015 is a defining year. With hindsight, we can clearly see that is the year when we crossed an invisible threshold into a different hydro-meteorological regime in western North America. We are now in Year Seven of this new reality. Yet only in 2021 is in finally sinking in with the population at large that something has fundamentally changed.”

“As of 2021, we can truly say that the era of weather extremes is upon. And it has happened faster than anyone had projected or expected. Think of the terms that are now part of the everyday vocabulary in weather forecasts on the evening news: heat dome, atmospheric river, cyclone bomb.”

Extremes are More Extreme

“We have always had weather extremes in British Columbia. In my experience, dry months would follow wet months. In other words, the duration of wet and dry periods was comparatively short. On an annual basis, things had a way of balancing out. Now, however, winters are warmer and wetter. And summers are longer and drier. This new reality has huge consequences for water security, sustainability, and resiliency.”

“A generation ago, for example, water supply managers could reasonably anticipate that three months of water storage would be sufficient to maintain supply during a dry summer. Today, however, a 6-month drought is a very real likelihood, and on a repeating basis. In the meantime, populations have also grown in the major centres. From a water supply perspective, think about the implications of a doubling in the need for water storage to make it through a drought.”

“When the water resource is large and water demand is small, variability is not that noticeable. But when the demand (Water OUT) is large relative to the available resource, a variation on the supply side (Water IN) magnifies the perception of impact. In many cases, BC communities have long been operating on narrow margins.”

“When you think about it, the planet Earth is a closed loop system. Mother Nature does not create new water.  The state may change – rain, snow, ice, vapour – but the water cycle is the water cycle. This means that extreme duration dry periods will of course will be followed by extreme duration wet periods. And that has been the pattern since 2015, with 2021 being the most extreme year of all as we have lurched from heat dome to epic atmospheric rivers.”

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Learn From and Build Upon Experience

“A key message is that climate change is not a driver; rather, it is another variable. Climate change is only one factor to consider when we talk about the nature and consequences of extreme weather. The real issues are uncertainty and risk, more specifically how we deal with the first and manage the latter.”

“At the same time, we must recognize that we have so transformed the landscape that there are compounding unintended consequences. These are due to our widespread interference with natural processes. In November 2021, there were numerous factors in play and these combined to magnify the impacts of extreme weather.”

“In particular, the  epic atmospheric river covered such a large area extending into the Interior that it resulted in a previously unimaginable scenario – a major storm coincident with high water levels in the Fraser River late in the year. In the lower Fraser Valley, this meant that inland drainage could not outflow by gravity through the dyke system and into the Fraser River. Normally the Fraser peaks in the late spring and early summer months due to snowmelt, not rainfall.”

“Another key message is that everything is connected. This requires an understanding of how the system works as a whole, rather than focusing on components in isolation of the whole. Thus, a constant challenge for planning is not to prevent past events, but instead is to use past experiences and apply systems thinking to inform and create flexible strategies for the present and the future,” concluded Kim Stephens.

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