Comparative Analysis of Urban Green Infrastructure in Flood Risk Reduction

Thesis Abstract

Urban flood vulnerability in rapidly expanding cities is exacerbated by inadequate understanding of how different configurations of green infrastructure (GI) mitigate flood risk under varying hydrological and urban? conditions. This study addresses the gap by conducting a comparative analysis of GI-led flood risk reduction across three typologies of urban landscapes high-density central districts, medium-density mixed-use suburbs, and peri-urban informal settlements, focusing on their capacity to reduce surface runoff, peak discharge, and local water retention. The aim is to quantify and compare the effectiveness of GI interventions in reducing flood exposure and to identify context-specific drivers of performance. Specific objectives are to (i) evaluate the hydrological performance of GI components (rain gardens, permeable pavements, green roofs, and urban forests) using calibrated hydrological models; (ii) assess residents’ perceived flood resilience and adaptation practices through structured survey data; (iii) examine governance, planning, and maintenance factors that influence GI functionality; (iv) test the relationship between GI effectiveness and spatial configuration using regression analysis; and (v) develop a comparative framework to guide policy and design decisions for scalable GI deployment. The study adopts a mixed-methods design integrating quantitative hydrological modelling and qualitative and quantitative social data. The population comprises urban areas within a mid-sized tropical metropolitan region. Samples include three study districts representing the GI typologies (n=60 survey respondents per district, total N=180) selected through stratified random sampling, and 15 well-characterized urban blocks subjected to detailed GI inventory and hydraulic simulation. Data collection instruments include (i) GIS-aided inventory forms for GI elements; (ii) rainfall-runoff data from local monitoring stations (12 months) and calibrated SWMM models to estimate performance metrics such as peak discharge reduction and runoff volume; (iii) structured questionnaires capturing residents’ flood experience, perceived resilience, and adaptation behaviors; (iv) semi-structured interviews with planning authorities, civil engineers, and maintenance agencies to explore governance arrangements; and (v) field measurements of soil infiltration rates and surface roughness to parameterize models. Analytical methods involve (i) comparative hydraulic performance assessment across districts using ANOVA and post hoc tests to detect statistically significant differences in peak discharge and runoff reduction attributable to GI configurations; (ii) multiple regression analysis to identify key predictors of GI effectiveness including green cover fraction, connectivity, soil infiltration capacity, and maintenance status; (iii) structural equation modelling to test the hypothesized pathways linking GI features to flood risk outcomes and resident resilience; (iv) thematic analysis of interview transcripts to extract governance and maintenance determinants; and (v) integration of quantitative and qualitative findings through a convergent mixed-methods synthesis to derive a comprehensive performance framework. The study also validates a transferability model that maps context variables (land use, population density, and rainfall intensity) to expected GI performance. Expected findings indicate that, across the three urban contexts, GI effectiveness in flood risk reduction is significantly higher where green elements are spatially connected, have shallow groundwater recharge potential, and are integrated with permeable surfaces and detention features. Peri-urban informal settlements may show lower runoff mitigation due to limited GI maturity and maintenance challenges, though community-based maintenance can enhance performance. Regression results are anticipated to reveal that GI effectiveness is positively associated with (a) higher canopy cover and soil infiltration rate, (b) reduced impervious surface fraction in surrounding micro-catchments, (c) proper maintenance regimes, and (d) visible governance support. Thematic analysis is expected to underscore governance fragmentation, funding constraints, and participatory planning as critical determinants of GI sustainability. This research contributes to knowledge by producing a cross-contextual, policy-relevant framework for evaluating urban GI as a flood mitigation strategy and by identifying design and governance conditions that maximize performance in diverse urban morphologies. Practical implications include guidelines for prioritizing GI investments, refining performance indicators, and structuring maintenance and governance arrangements to sustain hydrological benefits. The main conclusion anticipates that the flood risk reduction potential of urban GI is contingent on integrated design, robust maintenance, and adaptive governance, rather than GI presence alone. Recommendations include developing context-specific GI design templates, implementing standardised monitoring of hydrological performance, fostering community-based maintenance partnerships, and aligning urban development plans with flexible governance mechanisms to sustain flood resilience in rapidly urbanizing environments.