Blue roofs could help reduce the flooding effects of big storms

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This week:

• Blue roofs could help reduce the flooding effects of big storms
• An extravaganza of new emissions targets
• Here, there and everywhere: The problem of airborne microplastics

Blue roofs could help reduce the flooding effects of big storms

You've probably heard of a green roof, which sits on top of a building and is covered with vegetation. But what about a blue roof?

You might have guessed that it has something to do with water. Indeed, a blue roof collects stormwater through a pond system, temporarily stores it and gradually releases it afterward — offering a way to conserve water and prevent water damage. 

During a storm, rainwater can overwhelm urban sewer systems and send contaminated, untreated water into lakes and rivers. A blue roof could help solve this problem. 

"It's a new form of green infrastructure," said Rohan Hakimi, an engineer in integrated water management with Credit Valley Conservation in Ontario. Hakimi said the benefit of blue roofs is most evident in industrial commercial areas, which make up almost 30 per cent of commercial lands in cities. 

"When it rains in these areas, because of all these hard surfaces, the water doesn't have anywhere to go, so you get a lot of runoff and risk of flooding."

Water damage has become the leading cause of personal property claims in Canada, said Bruce Taylor, president of Enviro-Stewards, a company that provides businesses with sustainable solutions to environmental challenges.

He said our current urban infrastructure was not designed for the extreme weather conditions we are increasingly experiencing as a result of climate change. 

"With climate change, you won't get the same amount of precipitation but you get it in a shorter duration in bigger, shorter storms," Taylor said. "If you get water faster than you designed for, then it fills up and it starts backing up and you get flooding. And flooding is very expensive wherever that occurs."

A blue roof system stores rainwater and slowly releases it using flow-control devices or structures, from customized trays to existing building risers that cause water to dam up. Together, they act as a temporary sponge, collecting and then releasing the water over time. 

The stored water also provides the building with a cooling effect through evaporation, as well as additional water for reuse.

Enviro-Stewards will be doing an impact assessment for two community organizations based in London, Ont., including a food bank, where the water stored in the roof will be used for irrigation in their greenhouses and gardens, said Taylor. 

An "active" blue roof has a greater capacity than a "passive" one, allowing it to store water for a longer period of time and releasing it at a faster rate. Since the food bank doesn't have the pool liner required for an active roof, they implemented a slow-release roof drain as a passive blue roof.

Taylor said that blue roofs are more affordable than green roofs for the general population, although some jurisdictions have managed to successfully combine the two. For example, the RESILIO project in Amsterdam will install 10,000 square metres of blue-green roofs on social housing complexes (see photo above).

A blue-green roof incorporates the water storage layer below the green areas throughout the roof surface. When it rains, the water slowly supplies the necessary soil moisture for the plants and trees.

Enviro-Stewards is working with Credit Valley Conservation on a blue roof pilot project in Mississauga. They looked at the benefits of blue roofs in an industrial commercial neighbourhood — how they would capture and store water on the roofs of large buildings that were close together.

"We saw kind of a scaled-up impact that would really help to prevent flooding and provide other environmental benefits in these industrial commercial areas," Hakimi said.

"We're hoping through this project we can show and quantify more accurately those benefits and really help people see that this is actually possible."

— Vicky Qiao

Reader feedback

Last week, Matthew Lazin-Ryder wrote about the difficulty in finding the right metaphor to communicate the severity of climate change. 

Reader Madeleine Hart provided a multi-layered response.

"The article on metaphors for climate change made me think of a few conversations I've had over the years where I've tried to explain to someone during a heat wave that climate change is different than weather. Especially during heavy cold winters, people tend to always fall back on the idea that it means there's no climate change. I found using the metaphor of a broken home thermostat to be helpful. It's too cold, it's too hot… if you want your home to be comfortable, you have to fix the broken thermostat. Anyway, it may not be scientific or offer an easy solution, but it did seem to at least help those people move on from 'climate change isn't happening because it's snowing.' 

"The other issue that I've observed over the past 20+ years that I think has caused an overall perception problem is the fragmentation of environment protection: save the panda, save the whale, save the polar bear. I appreciate the sentiment and absolutely understand why that can be necessary. However, I think the result has been 20+ years of people seeing everything as a disconnected construct — if it's not directly in front of them or directly affecting them, they don't think about it or see a link to something they (we) are doing, buying, allowing to be done.

"The message has definitely improved over the years, where the broader picture of the ecosystem is brought into the conversation when talking about the decline of whales, caribou or polar bears, etc. But for those people who don't follow environment groups or regularly read the environment sections, they're still pretty disconnected. I have a friend who didn't know birds ate insects! How do you get to the age of 40 and not know that?"

Write us at whatonearth@cbc.ca.

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There's also a radio show and podcast! Building a new highway is often framed as a way to relieve traffic and congestion. This week, What on Earth looks at the proposal for Highway 413 in Ontario near Toronto and what it tells us about urban sprawl, green spaces and human health. What on Earth airs Sunday at 12:30 p.m., 1 p.m. in Newfoundland. Subscribe on your favourite podcast app or hear it on demand at CBC Listen.

The Big Picture: An extravaganza of new emissions targets

This week, U.S. President Joe Biden is hosting a (virtual) global summit on climate change. The meeting is momentous for a number of reasons. For starters, it confirms the U.S. is re-engaging with the rest of the world on environmental action. Secondly, it gathers countries at a time when a number of them are not on especially friendly terms. Finally, it has occasioned an array of ambitious new emissions targets for 2030. The U.K. announced a reduction of 68 per cent from 1990 levels. The European Union finalized a deal to reduce emissions in the 27-country bloc by at least 55 per cent (also from 1990 levels). During the summit, Biden confirmed that his government was seeking to cut U.S. emissions in half by 2030, a pledge that would require significant changes to its economy. Some wondered whether Biden's proposed pledge put pressure on Prime Minister Justin Trudeau to make deeper cuts. Whether or not that's true, Canada made a significant announcement of its own on Thursday, revealing plans to cut emissions by 40 to 45 per cent (from 2005 levels).

Hot and bothered: Provocative ideas from around the web

• Halifax-based CarbonCure Technologies is a co-winner of the prestigious NRG COSIA Carbon XPrize for its innovations in sequestering carbon in concrete — a feat that not only removes a greenhouse gas from the atmosphere, but also strengthens the concrete.

• This article suggests that Apple's newly unveiled iMac is a great example of "decoupling" — the idea that we can continue to make new consumer products while ensuring they put less and less strain on our natural resources. While stressing that Apple is "by no means perfect," the author points out that by using fewer materials and reducing emissions in the manufacturing process, iMacs have a significantly smaller environmental footprint than they did even a few years ago.

Here, there and everywhere: The problem of airborne microplastic

A new study has shown that large amounts of microplastic are floating into the atmosphere from roadways, oceans and farm fields. Once there, it can be carried by winds to the most remote places on Earth.

Airborne microplastic takes many forms and comes from many sources, but a key contributor is discarded plastic waste, according to the researchers, whose study was published in the Proceedings of the National Academy of Sciences.

Plastic biodegrades very slowly, and fragments into smaller pieces that can be carried by air currents. A significant percentage of these fragments comes from synthetic textile fibres.

"It can be either as really small fibres, films, what we call particles or even microbeads," Canadian researcher Janice Brahney told Quirks & Quarks host Bob McDonald, saying these tiny particles are "much smaller than what you could see with the naked eye." (The photo above shows microplastic particles seen through a microscope.)

Brahney, an associate professor of watershed sciences at Utah State University, worked with colleagues to investigate the sources of airborne plastic and how the plastic entered the atmosphere. 

The team first identified how plastic particles find their way into the atmosphere, focusing on sources and samples from the western United States. She and her team found three main ways this was happening.

"Highways and roads were really the most important variable for moving plastic into the atmosphere," said Brahney. "When a car passes over a road, it generates that energy that can move plastics high into the atmosphere. Imagine a car driving on a dirt road — you can see that plume of dust coming up after it. Within all that dust is also microplastic."

Another way microplastic ends up in the atmosphere is from the movement of ocean waves.

"Because microplastics tend to be a lot less dense than water, they're floating on the surface," said Brahney. "As the waves are churning and bubbles are bursting on the surface of the ocean, that has the capacity to emit these tiny particles into the atmosphere where they can then be transported." 

One thing that surprised Brahney and her colleagues was that their work showed more atmospheric microplastic makes its way from oceans to land, rather than the other way round. That's because the oceans hold more of what is called "legacy pollution" — decades-old particles that are now being picked up from the sea by winds and deposited on land.

The third way microplastic particles ended up in the atmosphere was as a result of agriculture. The researchers identified two major sources of plastic in agricultural soils. First, biosolids from wastewater treatment plants are used as fertilizer, and include significant amounts of plastic. Second, in recent years, plastic mulch has been used in significant amounts in agriculture and can enter soils. 

According to Brahney's models, plastic particles can stay in the atmosphere anywhere from a few hours to more than six days. "That's certainly long enough for plastics to travel in between continents and reach every corner of the globe," she said.

The impact of microplastic in the atmosphere is unclear to the researchers at this point. Brahney suggested the particles could influence atmospheric chemistry, including cloud formation, and therefore have some impact on weather. They could also affect the balance of solar radiation that we need for heat and energy.

It is hard to quantify the amount of microplastic in the air, but Brahney has generated an estimate based on her area of study. 

"Above the western United States, at any given time, there's about a thousand tonnes of microplastics in the air. And if we extrapolate that across the entire United States, we estimated about 22,000 tonnes per year. It's also estimated that we consume and inhale about a credit card's worth of microplastic every single week." 

— Mark Crawley

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Editor: Andre Mayer | Logo design: Sködt McNalty