Economic evaluation of green-roof environmental benefits in the context of climate change: The case of Hong Kong

Green roof offers multiple environmental benefits to urban ecosystems. Some of these benefits can aid cities in addressing global and local climate-change challenges. Many studies have attempted to convert a wide variety of green-roof benefits into economic values but few of them focused on climate-change aspects. This study assessed and valued six climate-related benefits in the compact city of Hong Kong based on localized experimental and modeling studies. The six benefits are thermal insulation, urban heat island (UHI) mitigation, avoided upstream emissions of carbon dioxide (CO2) and air pollutants, CO2 sequestration and air pollutants removal. Two roof greening scenarios, extensive (EGR) and intensive (IGR), were evaluated for their annual benefits and lifecycle cost-effectiveness under district-scale installation. Results suggest that large-scale green-roof installation can substantially reduce energy consumption, upstream emission and atmospheric concentration of CO2. Establishment of EGR in the study district Yau Tim Mong (YTM) has an annual total value of USD 12.98 million with unit value of USD 10.77 m−2 of green roof, and IGR, USD 22.02 million with unit value of USD 18.33 m−2. EGR is more economically attractive than IGR in terms of benefit-cost ratio (BCR) and payback period. The 40-year lifecycle BCR of EGR is 3.84 with a payback period of 6.8 years, while the equivalent values for IGR are 1.63 and 19.5 years, respectively. The study suggests a better integration of green roof into the current policy schemes in Hong Kong to combat climate change due to the notable benefits and cost-effective characteristics.