Improving stormwater retention in humid subtropical cities: environmental controls on green roof performance

Green roofs (GRs) are increasingly recognized as effective solutions for urban stormwater management, yet most research remains concentrated in temperate regions of Europe, North America, and Asia. This study investigates the hydrological performance of a GR under a humid subtropical climate (Cwa) in São Paulo, Brazil. The system retained 73% of total rainfall volume and achieved an average event-based retention of 82% during the monitoring period. Contrary to findings from temperate climates, no significant seasonal variation in retention was observed, indicating stable year-round performance. Rainfall volume was the main driver of retention. While the antecedent dry weather period showed limited predictive power, the antecedent precipitation index (API) offered improved explanatory capacity. A multiple linear regression model incorporating rainfall volume, API, and rainfall intensity explained 71% of the observed variability in retention. These findings underscore the consistent performance of GRs in subtropical environments and emphasize the importance of local climatic conditions when designing and modeling green infrastructure. The study provides practical insights for urban planners and policymakers aiming to enhance stormwater management strategies in diverse climate zones.