Basel, Switzerland: Green roofs : Combining mitigation and adaptation on measures

By 2100, under a high greenhouse emissions scenario, the temperature is projected to increase by about 4.5 ºC in comparison to the 1990s. This means that every second summer will be as hot or even hotter than the temperatures reached during the 2003 heat wave which caused severe loss of life across Europe. Extreme precipitation events are likely to increase in frequency and severity. Green roofs were found to offer opportunities to combine energy saving, climate change mitigation and adaptation, and biodiversity objectives. In densely built-up areas where providing extensive parks and planting trees may be impossible, vegetated roofs are a feasible greening option. These roofs not only mitigate the urban heat island effect but also act as insulators. By minimizing heat gains in buildings, they can lower the indoor temperatures by as much as 5°C and consequently reduce the need for cooling and the associated energy use, thus contributing to climate change mitigation and adaptation. Modelling studies conducted in Manchester, UK show that greening all the suitable roofs in densely built-up areas could reduce storm water runoff by 17–20%. Green roofs can also provide ‘stepping stones’ for migratory species under changing climate conditions. The main aim of the green roof initiative is to increase the coverage of green roofs in the city of Basel through the use of a combination of financial incentives and building regulations.

By 2100, under a high greenhouse emissions scenario, the temperature is projected to increase by about 4.5 ºC in comparison to the 1990s. This means that every second summer will be as hot or even hotter than the temperatures reached during the 2003 heat wave which caused severe loss of life across Europe. Extreme precipitation events are likely to increase in frequency and severity. Green roofs were found to offer opportunities to combine energy saving, climate change mitigation and adaptation, and biodiversity objectives. In densely built-up areas where providing extensive parks and planting trees may be impossible, vegetated roofs are a feasible greening option. These roofs not only mitigate the urban heat island effect but also act as insulators. By minimizing heat gains in buildings, they can lower the indoor temperatures by as much as 5°C and consequently reduce the need for cooling and the associated energy use, thus contributing to climate change mitigation and adaptation. Modelling studies conducted in Manchester, UK show that greening all the suitable roofs in densely built-up areas could reduce storm water runoff by 17–20%. Green roofs can also provide ‘stepping stones’ for migratory species under changing climate conditions. The main aim of the green roof initiative is to increase the coverage of green roofs in the city of Basel through the use of a combination of financial incentives and building regulations.

In many cities of Switzerland, green roofs became popular in the 1970’s as an element of ecological construction. Numerous green roofs were created in the 1980s, mainly as pilot projects, which provided a foundation of knowledge and experience for later initiatives. In addition, 1995 was the EU year of Nature Conservation. This provided the impetus for Basel’s first green roof campaign, which started in 1996. In the early 1990’s the City of Basel implemented a law to support energy saving measures. According to this law, which was the only one of its type in Switzerland, 5% of all customers’ energy bills are put into an Energy Saving Fund, which is then used to fund energy saving campaigns and measures. The national Department of Environment and Energy decided to pursue and promote green roofs using this source of funds. An investigation of the total number of green roofs resulted in 1711 extensive green roof projects and 218 intensive green roofs in the city of Basel. So, approximately 23% of Basel’s flat roof area was green roof in 2006. For developers, installing green roofs is now considered routine, and developers make no objections to installing them.

The case of Basel shows that even during a financial crisis a city can improve its citizens' wellbeing and its ecological structure with small-scale, concerted measures that are relatively cheap to implement.

• Green roofs are a type of green and blue space adaptation to climate change that brings multifunctional benefits: while the original entry point was energy-saving, the focus shifted to biodiversity, and then to the role of green roofs in adapting Basel to climate change.
• It is important to involve all stakeholders from the beginning of the initiative to address questions and concerns and ensure that everyone’s goals are being met.
• Leadership of the project by a committed individual dedicated to the initiative’s success.
• A comprehensive suite of mechanisms, from incentives to statutory regulations, has ensured a wide uptake of green roofs in Basel.

• The growing medium should be native regional soils — the regulation recommends consulting a horticulturalist.
• The growing medium should be at least 10 cm deep.
• Mounds 30 cm high and 3 m wide should be provided as habitat for invertebrates
• Vegetation should be a mix of native plant species.
• Green roofs on flat roofs over 1,000 square meters must involve consultation with the city’s green roof expert during design and construction.

Prior to the first incentive programme (1996-1997), the Department of Environment and Energy conducted a poll with the Swiss public to determine the level of support for an electricity tax to pay for energy-saving measures. The results of the poll favored a tax, and the City of Basel then explored energy-saving ideas, including green roofs. In 1996, a variety of stakeholders, including business associations and environmental organizations, were engaged by the City of Basel in the process of developing the green roof incentive programmes. The City led on the incentive programme, and the commitment of individuals from the Department of Building and Transport secured the political buy-in for the initiative. Various stakeholders were consulted when developing the green roof concept, and in establishing the first incentive programme. They included:

• the local business association,
• the horticultural association,
• the green roof association,
• the Pro Natura Basel environmental organization,
• the Department of Parks and Cemeteries in the City of Basel,
• the National Department of Environment, Forest and Landscapes.

Stephan Brenneisen and Nathalie Baumann

Zurich University of Applied Sciences Wädenswil

Grüental, Postfach 335, CH 8820 Wädenswil, Switzerland

E-mail: stephan.brenneisen@zhaw.ch; nathalie.baumann@zhaw.ch

Stadtgärtnerei Basel

Switzerland, Basel

http://www.stadtgaertnerei.bs.ch/

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