For those who don’t know, I have been living in Amsterdam for almost a year, and during this time, I have fallen in love with the city for many reasons.

It’s undeniably a beautiful city, but another aspect impresses me even more. Amsterdam is a functional, intelligent, interconnected city and a hub of innovation. Gradually, I am learning more and more how such a small country like the Netherlands can be a world reference in so many issues, especially environmental and social ones. Therefore, in this text, I would like to share an amazing project adopted here in Amsterdam: green roofs.

The city has expanded the planting of residential gardens on self-sustaining roofs that mitigate flooding and reduce city temperatures in an incredible way, which can serve as an example for other cities around the world, especially in Brazil.

Green Roofs

These roofs were designed to increase biodiversity in the city, cool neighborhoods on hot days, and prevent street flooding, something extremely valuable considering the volume of rainfall in the Netherlands. So far, more than 45,000 square meters of green roofs have been installed in Amsterdam. Between 2018 and 2022, the city implemented these green roofs in four flood-prone neighborhoods.

The project evaluation to date demonstrates that this approach is effective in mitigating stormwater runoff and combating the urban heat island effect. Like many cities, Amsterdam faces periods of heat and drought in the summer, along with extreme storms and flooding in the winter. In Europe, temperatures are rising faster than on any other continent — more than double the global average rate. Additionally, the winter climate of Northern Europe tends to present more extreme precipitation and flooding. It is estimated that more than 25% of buildings in Amsterdam are at risk of being affected by floods in the coming decades.

Innovation

The Netherlands serves as an inspiration for various things on a global scale, and one of them is innovative flood management in the face of climate change. Many of the country’s solutions are large-scale infrastructure projects, but smaller-scale efforts like green roofs are also super important for Amsterdam’s adaptation. There are also blue roofs designed to store rainwater and mitigate runoff impacts. When combined with green roofs, you get the added benefits of reducing urban air temperatures during heatwaves and increasing biodiversity. For the recent Amsterdam project, called Resilio, an “intelligent” factor was added, connecting multiple green-blue roofs via a digital network.

Decision Support System

Each roof has a smart valve that is part of a larger computerized system called the Decision Support System (DSS). This valve, when kept closed, retains rainwater on the roof to nourish the plants. The valves are connected to real-time weather forecasts and open when rain is expected. The system then slowly releases water into the city’s sewers. This prevents the city’s drainage system from overflowing and avoids major damage that can occur from flooding. And this leaves the green-blue roofs’ retention layer empty and ready to accept the next rainfall.

This system also has the potential to reduce street-level temperatures by 0.3°C, helping to reduce the urban heat island effect.

“You can cool the city as a whole by providing more evaporation and transpiration from the plants,” says Anna Solcerova, a researcher in water management and urban climate at the Amsterdam University of Applied Sciences.

Green-blue roofs allow much higher rates of water transferred to the atmosphere through evaporation than conventional green roofs — which reduces thermal stress in the city as a whole.

“There is a rule of thumb that for every 10 percent increase in surface vegetation cover, you cool the city by half a degree,” Solcerova says.

While conventional green roofs require drought-tolerant plants, the availability of water on Resilio’s green-blue roofs allows a wider range of native vegetation to thrive. “With a capacity of 60 or 70 millimeters, native plants can withstand drought periods of up to four weeks,” explains Spaan. This, in turn, attracts a greater diversity of insects.

These flourishing green spaces offer a resting or foraging place for wildlife — such as bees, butterflies, spiders, birds, and bats — and act as an ecological corridor for wildlife populations previously separated by human activity or structures. This is yet another innovation to solve various problems in urban areas: lowering temperatures, water runoff, increasing biodiversity in cities. Everyone wins.