During the past decade, thousands of Rotterdam building owners installed green roofs on their dwellings – about 330,000 square metres in total, almost 2% of the city’s 18.5 square-kilometre of flat roof space. But where some cities have promoted such projects to improve energy efficiency and absorb carbon dioxide, Rotterdam’s green roof infrastructure is all about water, and keeping as much rainwater run-off as possible out of aging, over-taxed sewers in order to prevent flooding.
About four-fifths of the Dutch port is below sea level. As Paul van Roosmalen, the city official overseeing sustainable public real estate, puts it: “The water comes from all sides” – the sea, the sky, the river and ground water. “It’s always been a threat.” But he also sees an opportunity to use a marriage of technology and green design to elevate the role of rooftops in managing Rotterdam’s water pressures.
While typical green roofs function like sponges and look like gardens, Rotterdam is working with public and private landlords to develop a “green-blue grid.” Instead of simply fitting out roof areas with plantings, these spaces can also be equipped with reservoirs or tanks to retain excess flow – blue roofs. The tanks, in turn, are equipped with electronic drain valves that can be opened and closed remotely, in some cases via a smart phone app.
“The problem,” says van Roosmalen, “is that when they’re full, they’re full.” The city’s vision, he explains, is to develop a system for coordinating the water levels in these tanks to help manage sewer capacity. The idea is to link the valve control devices into a grid of blue roofs that function, in effect, like a dispersed network of storm water reservoirs. When there’s rain in the forecast, the reservoirs can be drained automatically. Then, during heavy weather, they can store rainwater, reducing pressure and flooding in the sewer system.
While Rotterdam’s blue-green grid is still far from completion, it represents an example of how a set of digital sensing technologies can be potentially harnessed to produce a smart city solution to an urban sustainability problem.
The technological lynchpin in Rotterdam’s strategy has been the installation of a highly sensitive weather radar on the roof of the city’s tallest building. The device is capable of detecting rainfall 16 to 20 kilometres away. Remotely operated blue-green roof control systems can be programmed to dynamically respond to those forecasts and release water that sits in the reservoirs. (A similar project, the Resilience Network of Smart and Innovative Climate Adaptive Rooftops, or Resilio, is underway at several Amsterdam social housing complexes.)
As of 2021, Rotterdam officials were testing a pilot version of this grid. To scale it up, the city has to figure out how to co-ordinate with Rotterdam’s water board, which manages the sewer infrastructure, as well as property owners. The strategy potentially complements other water management planning moves, among them retrofitting public squares with “rain gardens” – i.e., clusters of water-absorbing shrubs and perennials planted in a small depression in the ground. “Instead of making bigger sewer pipes, we made a choice to invest in redesigning public space in a way that contributes to a nicer, better, more attractive district,” Arnound Molenaar, Rotterdam's chief resilience officer, told Thomson Reuters in 2019.
Van Roosmalen adds that a green roof can absorb about 15 milometres of rain per square-metre, whereas a roof with a reservoir can retain 10 times as much. The city’s goal is to convert one million square metres of flat roofs to include water retention systems and solar panels. Aggregated across even a portion of the city’s flat roofs, he says, “it’s a tremendous amount of water.”
The Netherlands' climate policies reflect a sense of urgency, given its exposure to sea level rise and flooding on rivers that flow into the country from the east. For that reason, both adaptation and mitigation have been central to the country's plans for future-proofing its cities.
Rob Schmidt, a sustainability policy expert with the City of Rotterdam, points out that the Netherland’s nine largest city-regions collaborate to develop and test approaches and technologies. “We learn from each other how to cope with these so-called smart city projects.” Each city has adopted a policy area: Rotterdam is focused on climate adaptation; Amsterdam, circular economy; Eindhoven, low-carbon mobility and energy transition, and so on.
The national government has launched an Urban Agenda that involves negotiating “city deals” many involving smart city projects that typically include multiple partners, including research institutions. “Our approach is focused on the opportunity and finding everyone you need to get to a solution,” says Urban Agenda program manager Frank Reniers. “You put them in a room and try to innovate your way out of the problem.”
“We learn from each other how to cope with these so-called smart city projects.”
-Rob Schmidt, a sustainability policy expert with the City of Rotterdam
The Netherlands wasn’t always so collaborative. According to Frank Kresin, dean of the Faculty of Digital Media and Creative Industry at the Amsterdam University of Applied Sciences, Amsterdam in the late 2000s and early 2010s “was doing everything in its power to become `smart.’” The city’s appetite for tech drove a great deal of investment in automation and digitization.
But the infatuation with these corporate solutions, Kresin wrote in a 2016 study, “had some flaws,” including the risk of excessive surveillance and an unquestioning embrace of the idea that the smart city was “a machine that needs to be optimized, with no consideration or understanding of the organic reality. It wants to maximize efficiency and avoid friction, so it simply and non-negotiably imposes top-down, non-transparent technological solutions.”
Kresin wasn’t the only one concerned about this drift. Beginning in the mid-2010s, citizens groups, entrepreneurs and academic institutions pushed Dutch policy-makers and companies to swap out the top-down approach in favour of a more grass-roots philosophy that features extensive public engagement, citizen-science projects and applied research.
“The big threat is loss of autonomy,” says Jan-Willem Wesselink of Future City Foundation, a Dutch network of municipal agencies, civil society organizations, universities and technology companies seeking to promote a democratic approach to smart urbanism that aligns with a U.N. social development goal (#11) about resilient, sustainable and inclusive cities. “Does Google or some other company decide how you use the city?”
Kresin describes one early effort at broadening the conversation. In 2014, Amsterdam Smart City, a tech incubator, distributed several hundred “smart citizen kits,” which provided rudimentary sensors to allow people to perform environmental indicator tests on water and air quality around the city. Their findings were fed to the city. While the readings fell short of research-grade data, this experiment in citizen science attracted many participants, generated upbeat media coverage and, in a few cases, led the city to clean up local beach areas. Its popularity also inspired Kresin and some colleagues to establish the Amsterdam Smart Citizens Lab, where civil society groups, academics and government officials work together to find solutions to other urban problems.
The distribution of the kits “was a surprisingly successful project,” says soil chemist Gerben Mol, a resilient cities researcher at Amsterdam’s Advanced Metropolitan Solutions Institute (AMS), a university-municipal government joint venture established to conduct more formal applied urban research.
In recent years, a growing number of Dutch city-dwellers are finding venues to engage in local conversations or projects about how to put urban data and technology to work in addressing the problems they see in their communities – in effect, a cultural, as opposed to corporate or bureaucratic, response. One example: an AMS project that created a composite out of a glue-like bacterial residue and de-contaminated wood fibre culled from septic waste (i.e., used toilet paper). A potential application is being tested to use this composite as a binding agent in road asphalt.
There are other more traditional tech ventures, such as Amsterdam Smart City, an incubator with numerous public and private partners, all working collaboratively to benefit the city. Community manager Nancy Zikken says the City of Amsterdam has “embraced” TADA.city, a network of European organizations that have pledged adhere to six core principles for digital city initiatives (inclusive, locally focused, controlled by residents, monitored, transparent and broadly accessible).
She also says that Amsterdam Smart City screens applicants, such as start-ups, to ensure their proposals align with broader policy goals and have what Zikken calls “social value.” As an example, she cites a firm that recently pitched a parking app but was rejected because it would likely encourage car use in a congested city that wants the opposite. “Most of the companies we’re working with really do see the value of incorporating citizens and using the wisdom of the crowd.”
In Rotterdam, city officials, who are driving the blue-green grid initiative, are also using public education, open houses and other engagement tools to promote these projects, many of which will be installed on privately owned dwellings, using private capital, if the strategy is to attain sufficient scale to make an impact.
Rotterdam, interestingly, hasn’t created financial incentives. Rather, in discussions with private property owners, Paul van Roosmalen says his team stresses the benefits and explains the options for what’s possible, for example combining a roof-top reservoir with solar. “They can pick what they think would add to the quality of their specific land,” he says. But there’s also a more urgent appeal, too: “You can save your city from drowning.”
Adapted with permission from Dream States: Smart Cities, Technology and the Pursuit of Urban Utopias (Coach House Books, 2022).
