Stuttgart: combating the heat island effect and poor air quality with ventilation corridors and green-blue infrastructure

Stuttgart sits in the wide Neckar basin, with the city centre at about 240m above sea level and surrounding hills rising to 500m. Wind speeds are generally low, which together with the urban heat island effect contributes to poor air quality. A 2016 study with the German Weather Service projects that heat-exposure days (daily max above 32C) in the city centre will double from 1971-2000 to 2031-2060, and that days with heat stress will increase significantly to 2050 (more than 60 days/year in the built-up Stuttgarter Kessel and Neckartal by 2050), rising further to the end of the century.

Facilitate air exchange and cool-air flow from the hills to the valley floor, protect urban natural areas, expand greenery, and promote green and blue infrastructure to improve adaptation to hotter summers and more frequent heatwaves.

The 2008 Climate Atlas for the Stuttgart region (building on urban climatology work since the 1980s, with an in-house climatology department existing since 1938) maps wind patterns, cold-air flows and pollution, classifying areas into eight categories with tailored planning recommendations (e.g. protecting valleys, hillsides and saddle topographies as air corridors, avoiding urban sprawl, and tree preservation orders above 80cm trunk circumference). It is being updated into an online tool under a BMBF-funded research project. Implementation is carried out by the Office for Urban Planning and Urban Renewal, with the Office for Environmental Protection's Section of Urban Climatology evaluating development proposals. Current expansion includes greening buildings, shading footpaths/bike routes and building facades, 'cool spots' with water features, a blue-infrastructure programme (drinking fountains, water elements), and the INTERESS-I pilot project testing blue-green infrastructure building blocks.

Over 39% of Stuttgart's surface area is protected for natural elements, and greenery covers over 60% of the city, comprising 5,000 ha of forest/woodland, 65,000 park/open-space trees and 35,000 street trees; over 300,000 m2 of rooftops have been greened, and 63 of 273 km of tram track (as of 2019) planted with oligotrophic grasses. 60 hectares of greenfield land were removed from the 2010 development plan. Since 2016 the city has provided about 2 million EUR/year via a green funding programme (still active), plus a one-off 12.7 million EUR for park renovation, about 850,000 EUR/year (2018-2021) to preserve inner-city vineyards/steep slopes for ventilation, 1.5 million EUR cumulative for private building greening, and (2020-2023) a 200 million EUR climate package including 20 million EUR for trees, hedges, forest conversion and green facades/roofs/courtyards.

Success factors include detailed in-house climatic/topographic knowledge enabling precise area-specific planning, decades of cumulative planning/landscaping action, use of existing regulation (the German Building Code) to mandate climate-related planning recommendations, close collaboration between the Office for Environmental Protection and City Planning/Renewal, and local framework plans (e.g. Talgrund/Stuttgart-West) explicitly addressing climate adaptation.