Cooling down
the city

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RESILIENCE
SOCIO-ECOLOGICAL SYSTEM

BY Hanny Roskamp


November 2018

In southern Europe, narrow streets and white buildings help stave off overheating. But the Dutch climate demands different solutions.

Dutch cities are turning into ovens, thanks to climate change. With materials such as bricks and concrete, and a lack of vegetation, the urban environment is not very resilient. Temperatures soar and on a hot day in the city it can be 10 degrees hotter than in the countryside or at the seaside. This is risky, especially for the elderly and other more vulnerable groups. So the search is on for solutions of all kinds.

Other types of construction

This is not a new problem. In the Middle East and around the Mediterranean, cities are often white and streets are narrow, creating a lot of shade. Associate professor of Landscape Architecture Sanda Lenzhölzer led the study on the resilience of the city. She says those narrow streets would not be a solution for the Netherlands. “The angle of the sun is different here, so you can’t just take over that way of building. And we are closer to the sea and the wind patterns are different. Every region requires a different approach.”

Large fountains provide a bit of cooling. The ‘Hide and Seek’ fountain in the garden of the Rijksmuseum in Amsterdam. PHOTO iStock

Together with teachers of Landscape Architecture João Cortesão and Rudi van Etteger of Wageningen University, Lenzhölzer is studying how the urban environment can be made more sustainable and resilient.

‘Channels, streams and canals are good for capturing excess rainwater, but their impact on the air temperature is zero’


Last summer, the municipality of Arnhem brought an underground stream, the Sint-Jansbeek, above ground in the city centre. This stream had been underground since the 19th century, with a vault built over it. The idea behind exposing the stream was that more water would cool down the concrete jungle, where temperatures are going up and up, partly due to climate change. An expensive project, while there was no certainty that it really would cool down the city.

Charming but pointless

The stream might lend the city more atmosphere, but Lenzhölzer and Cortesão’s research shows it won’t have much impact on the temperature. Cortesão: “Bodies of water such as channels, streams and canals are good for capturing excess rainwater, but their impact on the air temperature is zero. We have measured that in eight test situations such as city canals of various kinds in different Dutch cities. It would be better to put in large fountains; that would have a bit of a cooling effect.”

Left: Shade from the trees helps keep the apparent temperature in Nijmegen down. PHOTO Hollandse Hoogte. Right: A cool, narrow street in Otranto, Italy. PHOTO Shutterstock

Large bodies of water such as lakes and wide rivers can bring about cooling, but of all the possible methods, there is only a modest role for water elements. Cortesão: “Ventilation and shade can help reduce the apparent temperature much better. You can plant trees, for instance, but then they block the view. If we really want to make the city more resilient, it is important to take more aspects into account in our urban architectural designs. So that the city can withstand extreme temperatures or heavy rain better. Costs, the impact on traffic and on public health – the better you test a design on all these aspects, the more robust it will prove.

Rotterdam from the Euromast, with the cooling trees of a city park in the foreground. PHOTO Berlinda van Dam/Hollandse Hoogte

You should also make these aspects measurable, so that you know how much the temperature goes down if you plant a row of trees. We need to shift towards evidence-based design.” And of course, what the city residents think about it counts too. So Cortesão showed residents ‘before and after’ pictures. “All the designs for the water elements that we showed were considered as good as or better than the original situation.”

From failsafe to safe to fail

Heat is not the only problem in the city. Excess rainwater is increasingly a cause for concern, too. How can you develop a system that responds effectively to cold, heat, drought and excess water? An integrated approach is required. And maybe there have to be solutions that are no longer failsafe but more ‘safe to fail’, thinks Van Etteger. “We used to build ever bigger dykes and bodies of water, so that nothing could go wrong. But if something still does go wrong, a tsunami or a major dyke breach for example, the consequences are massive.

‘Ventilation and shade seem to help keep the apparent temperature down much better than water’

“In the future, there may be a shift to smaller public works, allowing for things to go wrong, but with less impact if they do. One of our students went to a typhoon region in Asia and ended up in… a typhoon. The whole island where she was staying got flooded, but it wasn’t a disaster because the islanders went with it. When the water comes in there, people move to higher ground, and when the typhoon is over, they come back. Just as we Dutch used to do with our mounds. That is quite a different principle to that of securing everything behind high dykes.”

The Municipality of Arnhem brought an underground stream, the Sint-Jansbeek, above ground in the city centre. PHOTO Hollandse Hoogte

Name

Sanda Lenzhölzer PhD

Position

Associate professor in Landscape Architecture at Wageningen University & Research

Name

João Cortesão PhD

Position

Assistant professor in Landscape Architecture at Wageningen University & Research

Name

Rudi van Etteger PhD

Position

Assistant professor in Landscape Architecture at Wageningen University & Research

Resilience research

The resilience of the city

Team

This research on societal resilience is being conducted by a team of scientists from four universities (4TU Resilience Engineering):TU Delft, TU Twente, TU Eindhoven and Wageningen University & Research

Research

The follow-up to this study is called DeSIRE, or Designing Systems for Informed Resilience Engineering. In this collaboration, the technical Universities of Delft, Twente and Eindhoven, and Wageningen University & Research will take an integral look at how you can design cities so they are adaptable both socially and technically. Lenzhölzer: “Water elements can be part of that but we shall be looking at many more urban architectural elements, and on a far bigger scale.”

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