Assessing the Impact of Green Roofs on Urban Stormwater Management in City Centers

Thesis Abstract

Urban centers increasingly face challenges related to stormwater runoff, which exacerbate flooding, water pollution, and sustainable water resource management issues. Green roofs have been proposed as an effective natural drainage solution, but comprehensive empirical assessments of their impact within highly urbanized city centers remain limited. This study aims to evaluate the effectiveness of green roofs in mitigating stormwater runoff, with specific objectives to quantify runoff reduction, analyze hydrological performance under varying climatic conditions, and identify best practices for integrating green roofs into urban stormwater management systems. Employing a mixed-methods research design, the study combines quantitative hydrological measurements with qualitative assessments. The population comprises 50 existing green roofs located within the central business districts of five metropolitan cities, selected through stratified random sampling to ensure diverse climatic zones, building typologies, and vegetation types. A sample of 30 green roofs is subsequently examined in detail, with data collected through in-situ sensors measuring runoff volume, peak flow rates, and soil moisture content over a 12-month period. Additional data are obtained via structured interviews with building managers and urban planners to contextualize technical findings. The data collection instruments include calibrated flow meters, moisture sensors, and semi-structured interview guides, ensuring validity and reliability through calibration procedures, pilot testing, and inter-rater reliability assessments. Data analysis employs descriptive statistics to outline baseline characteristics of green roofs, while inferential statistical techniques such as multiple regression analysis assess the relationship between green roof features and stormwater mitigation performance. Variance analysis (ANOVA) tests compare the effectiveness across different climatic zones and roof typologies. The study also develops a hydrological performance model based on the Stormwater Management Model (SWMM) framework, calibrated with field data. Theoretical underpinning draws on the Biophysical Theory of Urban Ecosystem Services and the Theory of Natural Drainage, providing a conceptual lens to interpret how green roofs contribute to urban hydrological regulation. Key findings are expected to demonstrate that green roofs significantly reduce peak runoff flows—by an average of 35% across monitored sites—and decrease total runoff volume during rainfall events, particularly under heavy precipitation conditions. Variations in performance are anticipated based on roof thickness, vegetation cover, and soil depth, highlighting the importance of design parameters. The analysis also expects to identify critical barriers to widespread green roof adoption, such as maintenance costs and structural constraints, as revealed through stakeholder interviews. This research advances the empirical understanding of green roof functions in urban stormwater management, filling marked gaps in the literature regarding long-term performance data and context-specific effectiveness. The developed hydrological performance model offers a practical tool for urban planners seeking to optimize green roof integration strategies. Furthermore, it contributes to the theoretical discourse by empirically validating the applicability of the Biophysical Theory and the Natural Drainage Theory within complex urban environments. The study culminates in conclusive evidence that green roofs can serve as a sustainable, nature-based solution to urban stormwater challenges, advocating for policy reforms to incentivize green infrastructure development. Recommendations include establishing standardized design guidelines, implementing maintenance protocols, and fostering multi-stakeholder collaboration to promote green roof adoption. Future research directions suggest exploring the microclimatic influences on green roof performance and assessing their cumulative impact on urban water resilience under climate change scenarios, thereby reinforcing the strategic role of green infrastructure in fostering climate-adaptive cities.