Design and Evaluation of Urban Green Roofs for Stormwater Management

Thesis Abstract

Urban areas worldwide are increasingly vulnerable to flooding, intensified by rapid urbanization, inadequate stormwater management infrastructure, and climate change. Green roofs have emerged as a sustainable solution to mitigate urban stormwater runoff; however, there remains limited empirical evidence regarding their optimal design, performance evaluation, and integration into existing urban drainage systems. This study aims to design and evaluate the effectiveness of different green roof configurations in stormwater management within an urban context, with specific objectives to (1) assess the hydrological performance of various green roof systems, (2) analyze the influence of substrate depth and vegetation type on runoff reduction, (3) develop a predictive model for green roof runoff behavior, and (4) provide practical recommendations for green roof design tailored to urban stormwater control. The research adopts an interdisciplinary approach grounded in sustainable urban drainage systems (SUDS) theory and the Theory of Planned Behavior, which inform the modeling of stormwater retention and stakeholder acceptance, respectively. The methodology employs a mixed-methods research design. Quantitative data are collected over a 12-month period from three pilot green roof installations installed on municipal government buildings, with each installation comprising five different configurations—varying substrate depths (10 cm, 20 cm, and 30 cm) and plant species (sedum, grasses, and native shrubs)—to ensure representativeness. A total sample size of fifteen green roofs is selected using stratified random sampling. Hydrological data are gathered through automated runoff meters, soil moisture sensors, and weather stations, providing continuous monitoring of stormwater retention capacity during diverse rainfall events. Qualitative data on stakeholder perceptions and maintenance practices are obtained through semi-structured interviews with building occupants, maintenance personnel, and urban planners. The reliability and validity of instruments are established through calibration and pilot testing, while data analysis involves descriptive statistics, multiple regression analysis for performance modeling, and thematic analysis for qualitative insights. Key findings are anticipated to reveal statistically significant differences in runoff reduction performance corresponding to substrate depth and vegetation type, with deeper substrates and native vegetation expected to exhibit superior stormwater retention. The regression models are projected to predict runoff volumes with high accuracy (R² > 0.85), facilitating scalable green roof design guidelines. The qualitative analysis is expected to highlight operational challenges, maintenance preferences, and policy gaps influencing green roof adoption. These findings will contribute novel empirical data to the body of knowledge on green roof hydrological performance, advancing understanding of optimal design parameters for stormwater control and fostering evidence-based urban planning policies. The study's contribution lies in providing a comprehensive, data-driven framework for designing more effective green roofs, integrating hydrological performance metrics with stakeholder perspectives. The research underscores the importance of tailored green roof configurations in maximizing stormwater retention and resilience to flooding in densely built environments. Concluding remarks emphasize the potential of green roofs as integral components of urban flood risk management, with recommendations including standardized design protocols, policy incentives, and targeted community engagement strategies to enhance adoption and sustainability. Suggestions for further research include long-term monitoring across different climatic zones and the incorporation of life cycle cost analyses to evaluate economic viability. Overall, this work aims to inform policymakers, urban planners, and environmental engineers on implementing green roofs as a viable structural and ecological intervention for sustainable urban stormwater management.