Integrated Urban Green Roofs for Stormwater and Heat Mitigation: Design, Implementation, Evaluation

Thesis Abstract

Urban intensification and climate variability exacerbate stormwater runoff and urban heat islands, challenging water management and public health in dense cities. This study investigates the design, implementation, and evaluation of integrated urban green roofs as a multifunctional strategy to mitigate stormwater peaks and surface temperatures while enhancing urban biodiversity and building energy performance. The aim is to develop a replicable framework for optimizing green roof performance through material selection, structural design, and maintenance protocols, and to quantify environmental and social outcomes in real-world settings. Specific objectives are (1) to synthesize design guidelines that couple hydrological performance with thermal regulation under different meteorological scenarios; (2) to implement pilot green roof systems on ten representative commercial buildings in a metropolitan core and monitor performance over two years; (3) to evaluate stormwater retention, peak flow reduction, evapotranspiration rates, and surface temperature differentials using continuous instrumentation; (4) to assess energy savings, indoor thermal comfort, and occupant perceptions; (5) to identify barriers to adoption and inform policy instruments for scalable deployment. The methodology adopts a mixed-methods design, integrating comparative quasi-experimental evaluation with qualitative insight. The population comprises commercial rooftops eligible for retrofitting within the metropolitan study area. A purposive sample of ten buildings is selected to represent varying roof substrates, slope, and structural capacity. Data collection employs (i) hydrological sensors (tipping-bucket rain gauges, soil moisture probes, lysimeters) and infrared thermography for continuous monitoring of rainfall capture, runoff coefficients, evapotranspiration, and roof surface temperatures; (ii) energy use intensity data from building management systems, quantified for pre- and post-installation periods; (iii) microclimate data from on-site weather stations; (iv) semi-structured interviews with facility managers and occupants, and focus groups to gauge perceived thermal comfort and acceptance. Instrument validity and reliability are ensured through calibration against standard meteorological data, repeat measurements, and pilot testing of the data collection protocol. Analytical strategies include (a) difference-in-differences analysis and hierarchical linear modeling to estimate the causal impact of green roofs on stormwater volumes and peak discharge reductions, accounting for rainfall intensity and antecedent moisture; (b) generalized additive models to explore nonlinear relationships between roof depth, substrate, plant species, and thermal performance; (c) ANOVA to compare energy savings across roof configurations; (d) thematic analysis of interview and focus group transcripts to extract barriers, enablers, and design considerations; (e) life-cycle assessment to evaluate environmental trade-offs of production, maintenance, and end-of-life scenarios. A conceptual model integrating hydrological, thermal, energy, and socio-behavioral dimensions guides hypothesis development and interpretation of findings, with theoretical anchoring in Urban Bioclimatology and Sustainable Urban Drainage System (SUDS) frameworks. Key expected findings include (i) quantified reductions in annual runoff volumes and peak flow during storm events, with variation by substrate depth and vegetation density; (ii) measurable cooling of roof surfaces and adjacent microclimates, translating into modest but meaningful reductions in cooling loads and improved indoor comfort; (iii) statistically significant improvements in building energy performance during hot seasons, with potential lifecycle energy and cost savings; (iv) identification of cost-effective green roof configurations that balance water retention with structural considerations; (v) nuanced understanding of social and organizational barriers to adoption and maintenance regimes. The study contributes to knowledge by delivering an evidence-based optimization framework for integrated green roofs that links design parameters to hydrological and thermal outcomes and demonstrates their implications for urban resilience. It informs policy by detailing scalable retrofit pathways, cost-benefit thresholds, and maintenance protocols aligned with municipal sustainability targets. The main conclusion anticipated is that well-designed, properly maintained green roofs can meaningfully attenuate stormwater peaks and urban heat exposure in dense urban areas, while delivering energy and social co-benefits, thereby supporting broader adoption through clear design guidance and governance recommendations. Recommendations include standardization of substrate depths and vegetation mixes for different roof types, integration with rainwater harvesting, incentives for retrofitting in high-risk neighborhoods, and continuous monitoring frameworks to guide adaptive management.