Urban heat islands: a cross-city comparative analysis in megacity resilience

Thesis Abstract

Urban heat islands (UHIs) in megacities exacerbate thermal stress, energy demand, and socio-spatial inequities, challenging resilience planning in rapidly urbanizing contexts. This study addresses the problem of divergent UHI intensity and coping capacity across comparable megacities, seeking to understand how climatic, built-environment, and governance factors shape resilience outcomes. The aim is to compare UHI dynamics and adaptation responses across three global megacities—Los Angeles, Shanghai, and Lagos—to identify commonalities and context-specific drivers of resilience and to inform integrated mitigation strategies. The specific objectives are (i) to quantify spatial variability in land surface temperature (LST) and urban form indicators at multiple urban scales; (ii) to assess the effectiveness of current adaptation measures (green infrastructure, reflective surfaces, and cooling centers) in modulating thermal stress and energy demand; (iii) to analyze governance, policy coherence, and stakeholder participation as mediators of resilience; (iv) to model the relationship between UHI intensity, human health outcomes, and energy consumption using a multi-city comparative framework; and (v) to develop a framework of best practices for cross-city resilience enhancement under UHIs. The methodology adopts a comparative cross-city design integrating remotely sensed, socio-economic, and policy data. The population comprises urban districts within the core metropolitan areas of the three megacities. A stratified random sample of 180 neighborhoods per city (total N=540) is drawn to capture housing types, land cover, and socio-economic diversity. Data collection employs (a) satellite-derived LST and Normalized Difference Built-Up Index (NDBI) at 30 m resolution from Landsat 8 and Sentinel-2 for two recent dry and wet seasons to capture temporal variability; (b) GIS-based land-use and green-cover metrics; (c) municipal and utility records on energy consumption, health clinic admissions for heat-related illnesses, and cooling center usage; (d) household surveys (n=1,800; 300 per city) to measure perceived thermal comfort, adaptation strategies, and vulnerability indicators; and (e) key informant interviews with urban planners, policy makers, and NGOs (n=45) to assess governance mechanisms. Instruments include structured survey questionnaires, remotely sensed data processing scripts, and a semi-structured interview guide. Data analysis proceeds in a sequential, integrative manner. Descriptive statistics reveal inter-city and intra-city patterns of UHI intensity and socio-demographic variables. Spatial analysis uses geographically weighted regression (GWR) to model the relationship between LST, urban form (albedo, vegetation fraction, impervious surface), and socio-economic factors across cities. Hypothesis testing examines H1, that higher green infrastructure density reduces UHI intensity; H2, that governance quality moderates the impact of UHI on health and energy demand; and H3, that socio-economic vulnerability amplifies thermal stress. A multilevel mixed-effects model assesses cross-city differences in resilience outcomes, with city as a random effect. Thematic analysis of interviews identifies governance barriers and enablers, supplemented by a cross-city synthesis of policy instruments aligned with the Sustainable Urban Development paradigm. A conceptual model integrating physical, social, and institutional dimensions of UHI resilience guides interpretation. Expected findings anticipate that while all three megacities exhibit pronounced UHIs, the magnitude and responses vary Shanghai demonstrates strong cooling effects from dense green corridors but limited equitable distribution of benefits; Los Angeles benefits from decentralized microclimate adaptations yet faces equity gaps in vulnerable neighborhoods; Lagos shows rapid urbanization outpacing green infrastructure, resulting in higher exposure and energy burden, yet with high informal community-led cooling initiatives. The study is poised to contribute to knowledge by advancing a robust cross-city framework for UHI resilience that links physical urban form, health and energy outcomes, and governance processes, thereby filling a gap in comparative mega-urban studies. Policy implications include prioritizing equitable expansion of green and reflective surfaces, contextualizing resilience measures to local institutional capacities, and fostering cross-city learning platforms for urban climate adaptation. The conclusion emphasizes integrated planning that couples climate-responsive infrastructure with participatory governance, recommending scalable, context-sensitive action plans and standardized monitoring to track progress in reducing thermal inequities and enhancing megacity resilience.