InfraRed Investigation in Singapore (IRIS) Observatory: Urban heat island contributors and mitigators analysis using neighborhood-scale thermal imaging

TL;DR

This study addresses urban heat island analysis at the neighborhood scale in Singapore by integrating rooftop infrared thermography with a campus weather-station network to quantify heat fluxes from building façades, vegetation, and traffic. It introduces a calibrated heat-balance framework, expressing $Q^*$ as the sum of convective, conductive, and storage terms ($Q_H$, $Q_G$, $ abla Q_S$) with vegetation’s latent term $Q_E$, and a traffic component derived from vehicle detections, alongside a sensitivity analysis via Sobol indices. Key findings show concrete façades contribute to nighttime heat through longwave emission, while vegetation mitigates warming through evapotranspiration-driven latent flux, and traffic heat is small for limited road coverage. The approach demonstrates the value of high-temporal-resolution, neighborhood-scale thermal imaging for informing UHI mitigation and points to future work with additional observatories and data-driven city-scale models or digital twins.

Abstract

This paper studies heat fluxes from contributors and mitigators of urban heat islands using thermal images and weather data. Thermal images were collected from an observatory operating on the rooftop of a building between November 2021 and April 2022. Over the same period, an automatic weather station network was used to measure weather conditions at several locations on a university campus in Singapore. From data collected by the observatory and the automatic weather station network, a method was developed to estimate the heat emitted by building facades, vegetation, and traffic. Before performing the analysis of urban heat fluxes, it was observed that the surface temperature collected from the observatory is sensitive to some variables. After the sensitivity analysis, thermal images were calibrated against measurements of the surface temperature in an outdoor environment. Finally, several contributors and mitigators of urban heat islands were analyzed from heat fluxes assessed with thermal images and weather data. According to thermal images collected by the rooftop observatory, concrete walls are an important contributor to urban heat islands due to the longwave radiation they emit at night. Vegetation, on the other hand, seems to be an effective mitigator because of latent heat fluxes generated by evapotranspiration. Traffic looks to be a negligible source of heat if considered over a small portion of a road. In the future, more efforts can be made to estimate the magnitude of the heat released by an air-conditioning system from thermal images.

Figures (15)

• Figure 1: Observatory installed in the university campus in Sinagpore
• Figure 2: Positions where thermal images were recorded by the observatory.
• Figure 3: Weather stations installed in a university campus by yu2020dependence.
• Figure 4: Positions where sensors were installed to measure the surface temperature and calibrate thermal images.
• Figure 5: Built-up surfaces and green areas that were considered to analyze urban heat fluxes from the observatory.