Anke Wolff (Germany) 1; Matteo Roggero (Germany) 1
1 - Humboldt-Universität zu Berlin
Cities are increasingly exposed and highly vulnerable to climate-change related weather hazards such as extreme precipitation or heat waves. Nature-based solutions have emerged as a promising and sustainable urban climate adaptation option. Green roofs provide individual benefits such as greater thermal performance or improved roof insulation, and well-documented collective environmental benefits in terms of stormwater attenuation, heat mitigation or air purification. However, a critical mass of green roofs is needed to achieve environmental effects on an urban scale. Various public and private actors are involved in the installation of green roofs on residential, municipal and commercial buildings. Due to the combination of individual and collective benefits (or positive externalities), green roofs qualify as ‘merit goods’. These socially desirable goods are likely to be under-produced and -consumed because of unequal distribution of income, lack of perfect information and uncertainty as to their future benefits. The divergence between social and private costs and non-excludability of beneficiaries lead to social dilemmas and provide a rationale for public intervention. This paper aims to identify green-roof policies of environmental frontrunner cities and analyse their effect, individually and as a policy mix, on the green-roof area per capita, testing the theory that coercion or/and special incentives lead to an increased provision of socially desirable goods in large groups.
The analysis encompasses 21 cities from Europe, North America, Asia, Australia. Cases were mainly selected based on known green roof policies and available green roof data. The data was collected through literature & document analysis and semi-structured interviews. Qualitative Comparative Analysis (QCA) is used to pinpoint cross-case patterns and address causal complexity.
We find that green-roof areas vary substantially and range between 0,01 and 6,02 m2/capita. Different municipal policies are applied to develop green-roof areas in cities that can be broadly grouped into three categories: regulatory requirements, incentives, capacity and awareness building. The leading cities have mandatory regulatory requirements for all new developments. Some also have financial support programmes for retrofitting of existing flat roofs and indirect incentive schemes. The policy mix is always complemented by capacity and awareness building activities.
The preliminary analysis leads to the tentative conclusion that coercion may be required for the provision of socially desirable goods in cities.