Advocates for living roofs, those lush, plant-covered patches of green on our city buildings, have long championed these slices of eco-paradise in our urban jungle. Now, thanks to a pioneering project between Auckland Council and the University of Auckland, we have the data to prove their value.

The Living Roof Monitoring project was launched to assess how well these verdant rooftops perform compared to conventional ones. After months of careful monitoring, the results highlight their effectiveness as a sustainable urban solution.

Stormwater superstars

Auckland Council’s Senior Healthy Waters Specialist Rachel Devine highlights the global success of integrating nature into urban infrastructure. She explains that planting vegetation on rooftops is one of the ways that cities can effectively absorb rainfall, reduce flooding and mitigate the stormwater network from becoming overwhelmed.

“But now, having the local data to back this up gives us context that is relevant to Auckland’s climate and environment,” Ms Devine says.

University of Auckland Professor Asaad Shamseldin who leads the research with Dr Kilisimasi Latu and Dr Conrad Zorn, is pleased with the robust dataset collected by the team’s PhD students Aung Naing Soe and Sihui Dong, which focuses on assessing the benefits of plants over conventional coverings on rooftops.

Their findings show living roofs significantly reduce stormwater runoff, with some substrate types retaining nearly 80 per cent of rainfall, even during heavy downpours. And that almost every drop is retained in light rainfall, demonstrating the excellent absorption potential of these gardens.

Chair of the Policy and Planning Committee Councillor Richard Hills says the findings of this research are very promising for roof gardens, helping to prevent flooding and water pollution in built-up urban areas like the inner city.

“This preliminary research indicates that if we could retrofit roof gardens all over Auckland’s city centre it would not only enhance our place as a clean green city on the global stage but would also be a viable aid in reducing heat and help prevent or reduce flooding in parts of the city centre.

“It would also make the city look more beautiful for residents in high rise apartments, staying in hotels or working in offices and provide tangible environmental benefits, including providing habitats for native plants and birds.

“Stormwater run-off in the city centre also contributes to the pollution of the Waitematā and the Hauraki Gulf, and these findings point to roof gardens curtailing much of this run-off into our precious oceans and harbours.

Nature’s air conditioner: cooling our concrete jungles

Professor Shamseldin adds it is important to remember living roofs aren’t just about stormwater management; they are also very effective at keeping things cool.

“When urban temperatures rise, green roofs act like nature’s air conditioners,” says Professor Shamseldin.

In Auckland’s hottest months, when temperatures can exceed 25°C, the data shows living roofs lower rooftop surface temperatures by an impressive 32 per to 56 per cent. The research even uncovered a surprising ally in urban cooling: the wind.

“During the day, sea breezes help cool green roofs and delay peak temperatures, while at night, city-to-sea winds help reduce the temperature difference between green and conventional rooftops,” explains Associate Professor Shamseldin.

This translates to tangible energy savings for buildings and a potential reduction in the Urban Heat Island effect – truly, a breath of fresh air from above.

A living legacy: onshore islands

The pilot study was inspired by Auckland’s Central City Library living roof, a project developed in partnership with Ngāti Whātua Ōrākei that was launched five years ago.

Featuring over 2,000 hardy native plants, the roof reflects a shared commitment to enhance urban biodiversity and live in harmony with te taiao (the natural world).

“Kaupapa like this green roof are examples of cultural infrastructure, they integrate nature into our cities and allow us to actively elevate the mauri of our taiao,” says Etienne Neho of Ngāti Whātua Ōrākei.

Greener cities, smarter cities: a vision for the future

This collaboration already has the potential to influence Auckland’s future. By providing policymakers and urban planners with data, the project can inform smarter, greener development decisions that enhance urban environments.

“If we want to create a sustainable, healthy city, one that future generations can enjoy - working with nature is a must,” adds Ms. Devine.

“These results prove what we’ve long suspected: nature-based solutions can help our journey towards becoming a more sustainable and resilient city.”

The research team continues to monitor additional biodiversity benefits, and more updates will follow as the data flourishes. Although urbanisation and climate change present numerous challenges, one thing is certain, working with nature is a positive step towards a healthier urban environment.

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