Multiparameter vegetative stress index to estimate green roof well-being within urban green infrastructure

Nature-based solutions are increasingly being adopted worldwide to enhance urban sustainability and mitigate climate change impacts. Among them, green roofs (GRs) are widely promoted through policies offering technical support, tax benefits, and financial incentives, with some cities mandating GRs in new buildings. Since vegetation drives most GR-related benefits, such as urban heat island (UHI) mitigation, stormwater regulation, biodiversity, and carbon capture, monitoring its well-being is essential. This study introduces two novel satellite-based indices to assess GR vegetation health. The Vegetative Stress Index (VSI) is a single-parameter tool that tracks annual vegetation growth trends. The Multiparameter Vegetative Stress Index (MVSI) integrates climatic and urban variables to evaluate their combined influence on the Normalized Difference Vegetation Index (NDVI). Both indices were applied to Lisbon, Portugal, named European Green Capital in 2020 for its efforts in expanding green spaces. Results demonstrate that VSI and MVSI effectively capture long-term improvements in vegetative well-being across GRs, reflected in significant NDVI increases. Compared to other urban green spaces, GRs show enhanced vegetation resilience, underscoring their added value. These indices offer a practical, scalable method for urban planners and policymakers to monitor and support green infrastructure development and performance over time.