Assessing financial subsidies for green roofs: A micro-scale analysis of Lisbon (Portugal)

Green roofs (GR) provide ecological, economic, and socio-environmental benefits reducing the negative effects of urbanization and improving cities' resilience to tackle climate change. However, from the private investors' perspective, GR are economic unfeasible making necessary the development of public incentive policies. The study aims to assess adequate methodologies to design GR financial subsidies at the city scale, considering the influence of green roofs' ecosystem services (ES). The initial hypothesis is that constant financial subsidies are suboptimal, and it is necessary to develop more granular approaches. A cumulative and incremental 3-level costbenefit analysis (CBA) was performed at an urban micro-scale to allow the incorporation of environmental features in the monetary conversion of ES. Results confirm that positive ES provided by green roofs vary across the city. Consequently, constant values of financial subsidies at the city scale do not optimize public financial resources management, confirming the initial hypothesis. Moreover, findings reinforce the need to review the procedures for developing and granting public incentives at the municipal and/or macro-scale level for GR, especially as these solutions provide ES that are strongly influenced by environmental surrounding characteristics.