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

ABSTRACT Green roofs (GRs) are increasingly recognized as effective solutions for urban stormwater management, yet most research has been conducted in temperate regions of Europe, North America, and Asia. Evidence from humid subtropical climates, particularly in Latin America, remains limited. This study evaluates the hydrological performance of an extensive GR in São Paulo, Brazil, under a humid subtropical (Cwa) climate. During the monitoring period, the system retained 73% of total rainfall and achieved an average event-based retention of 82%. Unlike results reported for temperate climates, no significant seasonal variation was detected, indicating consistent year-round performance. Rainfall volume was the main driver of retention, while the antecedent dry weather period (ADWP) had limited predictive value. In contrast, the antecedent precipitation index (API) offered stronger explanatory capacity, and a multiple linear regression model combining rainfall volume, API, and rainfall intensity explained 71% of the observed variability. These findings highlight the strong potential of GRs to provide reliable hydrological benefits in humid subtropical cities and fill an important regional knowledge gap. In addition, the study provides practical insights for GR modeling by highlighting the importance of adopting climate-representative predictors, supporting the development of more accurate and locally adapted green infrastructure strategies.