Urban Green Roofs for Carbon Sequestration and Urban Heat Island Mitigation: A Multi-City Comparative Study

Project Abstract

Urban Green Roofs (UGRs) present a multifaceted approach to addressing climate and urban environmental challenges by combining ecosystem services with built infrastructure across diverse metropolitan contexts. This study conducts a multi-city comparative analysis to quantify the carbon sequestration potential and the mitigation of urban heat island (UHI) effects attributable to extensive and intensive green roof systems, integrated with local climate, building stock, and maintenance regimes. We synthesized a dataset spanning five major cities with varying climatic zones, architectural typologies, and policy frameworks, employing a mixed-methods design that couples empirical field measurements, remote sensing-derived surface temperature and albedo data, and carbon budget modeling. Field experiments deployed standardized green roof plots that capture substrate depth, vegetation type, soil organic content, moisture regime, and fertilization practices, enabling robust comparison of biomass accumulation, soil organic carbon (SOC) sequestration rates, and net ecosystem carbon balance over a three-year period. Simultaneously, we analyzed high-resolution thermal infrared imagery and in-situ temperature loggers to characterize diurnal and seasonal temperature differentials between vegetated rooftops and conventional roofs, thereby assessing UHI attenuation at the neighborhood scale. The carbon dynamics were evaluated through allochthonous carbon inputs, respiration fluxes, and the stabilization of SOC, incorporating the effects of irrigation, stormwater management, and roof-substrate microclimates. Findings indicate that well-designed UGRs can contribute appreciably to measurable carbon sequestration, particularly when vegetation communities include deep-rooted, perennial species with substantial biomass and when soil organic layers are managed to maximize SOC stabilization. In parallel, UGRs demonstrated variable yet significant reductions in rooftop surface temperatures, translating to lower ambient indoor temperatures and reduced cooling energy demand in adjacent buildings, with magnitudes contingent on roof insulation, building orientation, and urban morphology. The study also identifies trade-offs and constraints, including maintenance intensity, water use, substrate weight limits, and initial capital costs, which interact with climate resilience objectives and policy incentives to shape long-term performance. Through scenario analysis, we project cumulative climate benefits and energy savings over a 20-year horizon under different maintenance regimes, irrigation scenarios, and policy supports, highlighting the conditions under which UGRs yield the highest net societal value. The work contributes to the body of evidence supporting scalable green roof implementation as a nature-based solution for climate adaptation and mitigation in dense urban environments and offers a framework for standardized monitoring, data interoperability, and decision-support tools for city planners, facility managers, and researchers. Keywords green roofs, urban heat island, carbon sequestration, remote sensing, SOC, energy savings, urban sustainability, multi-city comparison.

Project Overview

What This Project Is About

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This project looks at how green roofs on buildings can help capture carbon from the air and reduce the urban heat that makes cities feel uncomfortable. It compares several cities to see how different roof setups perform in real-world conditions.

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The Problem It Addresses

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Cities are heating up due to lots of concrete and little green space, and buildings release carbon. Green roofs could lower temperatures and sequester carbon, but we don’t know which designs work best across different cities or how big the effect is.

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Objectives of the Project

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1. Assess how much carbon is captured by different types of green roofs.
2. Measure changes in surface and air temperatures in buildings with green roofs versus conventional roofs.
3. Compare results across multiple cities with varied climates and building types.
4. Identify design features that maximize cooling and carbon uptake.
5. Provide practical guidelines for implementing effective green roofs.

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What You Will Do Step by Step

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1. Review existing studies on green roofs and urban heat and carbon effects.
2. Select study sites in several cities and collect roof design data.
3. Install or use sensors to measure temperature, humidity, and solar radiation on selected roofs.
4. Collect data on roof vegetation, substrate depth, and maintenance.
5. Analyze how roof features relate to temperature changes and carbon capture.
6. Compare results between cities and identify common patterns.
7. Draft guidelines for best-performing roof designs.

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Expected Outcome

Expect to quantify the cooling benefits and carbon uptake of different green roof designs and to produce cross-city recommendations for optimizing performance and costs.