Localizing and prioritizing roof greening opportunities for urban heat island mitigation: insights from the city of Krefeld, Germany

Abstract

Context: Climate change may increase the frequency, intensity, and occurrence of urban heat islands (UHI) in cities worldwide, often with harmful impacts on citizens. Strategic planning and implementation of multifunctional green roofs promises to help mitigating UHI effects, but cities often lack up-to-date scientific understanding of best-suited locations. Objectives: The aim of this paper is to develop and apply a socio-ecological approach to explore and prioritize present and prospective opportunity spaces for roof greening based on remote sensing data to mitigate UHI effects. Methods: The city of Krefeld, Germany, serves as a case study. The research design consists of three steps, applied to the conditions of 2019 and a 2030 scenario: (i) Examining residents’ vulnerability to heat, (ii) Assessing existing green roofs and potentials for greening, and (iii) Prioritizing opportunity spaces for roof greening to reduce UHI effects. Results: Findings showed that the area of high vulnerability due to combined high heat exposures and densities of sensitive residents in Krefeld accounts for almost 300 hectares in 2019 and may triple until 2030. More than 90% of evaluated horizontal roofs have no vegetation cover. Highest priority for roof greening is attributed to 59 ha and 113 ha of roofs in 2019 and 2030, respectively. Conclusions: The findings can inform strategic roof greening efforts for climate adaptation, e.g. for the extension of cadasters, and facilitate communication to increase understandings, public and policy support, and implementation.