Cooling with green corridorsStuttgart is a forerunner in the protection of greenspaces. Using green ventilation corridors and construction bans at strategic places, Stuttgart has not only protected its climate with winds that hinder overheating. It has also improved air quality and increased resilience against global warming. With the support of detailed local climate maps, Stuttgart has stopped planned construction totalling over 60 hectares in recent years.
Keywords: greenspaces, overheating, air quality, climate maps, construction-bans
Stuttgart's work with climate maps goes back decades. The city sits in a basin of two river valleys, and therefore has problems with overheating and air quality (see also Vitoria-Gasteiz). That the city is also the centre of the German car industry does not make things better. Already in 1938, the problems were highlighted by a meteorologist hired by the city to analyse the local climate. The situation got worse in the 1970s and a more comprehensive effort began.
In 1992, Stuttgart published its first climate atlas. It showed how the topography and buildings influence the flowthrough of air. It was clear that the surrounding hills, up to 300 metres high, the nearby forests and the agricultural areas constituted the main sources of fresh air for the city. Stuttgart's topographical profile creates thermal winds at night down the hillsides and through the city. Problems were caused by increased construction on the hills, that replaced vinyards and trees, and thereby blocked the flow of air.
Climate atlas a cool tool
On the basis of the climate atlas, Stuttgart established an environmental office with the task to evaluate planned buildings' effects on the local climate, and develop control systems to protect key areas and increase the greenspaces in the city. The environmental office could use the support of national and regional legislation protecting greenspaces, and national building laws that after a 2004 revision integrated sustainability principles and even paragraphs on greenspaces and air quality.
The latest climate atlas from 2008 covers the entire Stuttgart region with its 2.7 million inhabitants. It shows in detail the flows of cold air and concentrations of air pollutants. It also categorises the local environment into eight types, based on significance for climate. Each type receives its own recommendations. In ventilation corridors for cold air, and in other open areas with large significance for the climate, no new construction is allowed. In built areas with large significance for the climate, increased vegetation and greenspace are recommended. In addition, the following principles guide planning:
- greenspaces shall surround buildings and larger interconnected green areas shall be protected and created
- valleys, hills, and hillsides shall not be built up
- urban sprawl shall be avoided
- in connection with industrial building, air pollutants in the surrounding settlements shall be avoided
The green areas in Stuttgart are also protected by local regulations. The motto for Stuttgart's land-use plan for 2010 is urban-compact-green (see also Wellington). All larger trees in the city centre are protected. Since 1992 a programme lets inhabitants adopt trees. Since 1986, the city has subsidised green roofs, which has led to Stuttgart becoming a leader in the field, with more than 300,000 sq m of green roofs (see also Chicago and Malmö). More than 60% of Stuttgart's area is green area and more than 39% is protected – the highest percentage in Germany. The city has 5,000 ha of forest, with 65,000 trees in parks and 35,000 along streets. Since the 70s, the city has integrated green areas into a large green “U”, which now makes it possible to go through park environments all the way from the central royal gardens to the forests at the city's edges.
The most important result of the latest climate atlas is the prohibition of new construction on the hills around the city and in ventilation corridors, despite great interest from developers to build there. In the land-use plan from 2010, planned construction projects totalling more than 60 ha were stopped due to greenspace protection.
Spreading to other cities
Several other German cities have followed in Stuttgart's footsteps, among them Berlin, which has developed a comprehensive environmental atlas for the city. The idea has even spread internationally to places such as Kobe, Japan, which created a climate atlas as the basis for measures to promote sea breezes during daytime and thermal winds from the mountains at night.
A. Kazmierczak, J. Carter, 2010, "Stuttgart: Combating heat island and poor air quality with green aeration corridors", Adaptation to climate change using green and blue infrastructure. A database of case studies. http://www.grabs-eu.org/membersArea/files/stuttgart.pdf
"Stuttgart: Cool city", Sustainable Cities, http://sustainablecities.dk/en/city-projects/cases/stuttgart-cool-city
City of Stuttgart, ”Climatic conditions in Stuttgart”, http://www.stadtklima-stuttgart.de/index.php?climate_in_stuttgart
Juergen Baumueller, Ulrich Hoffmann, Uwe Stuckenbrock, ”Urban Framework Plan Hillsides of Stuttgart”, The seventh International Conference on Urban Climate, 29 June - 3 July 2009, Yokohama, Japan, http://www.ide.titech.ac.jp/~icuc7/extended_abstracts/pdf/375531-1-090501004614-003.pdf
Siemens, German Green City Index, Stuttgart, http://www.siemens.com/entry/cc/en/greencityindex.htm
Greenroofs.com – The Green Roof Industry Support Portal, Industry Support,
Green Roof – Augustenborgs Botanical Roof Garden, “What is a Green Roof?”, http://www.greenroof.se/?pid=19
Key data are retrieved from the UN World Urbanization Prospects, the 2009 Revision, http://esa.un.org/unpd/wup/index.htm