Enhancing microclimate modeling in tropical climates: validation of Envi-Met with experimental data from Reunion Island

By 2050, the global urban population will increase by more than 2.5 billion, mainly in tropical and subtropical regions, according to the IPCC. The anticipated global warming of 1.5°C would exacerbate the already present heatwaves in urban areas. It is crucial to quickly adopt climate change adaptation strategies, particularly in tropical climates, to avoid severe consequences.

The urban heat island (UHI) phenomenon, where temperatures in urban areas exceed those in rural surroundings, is exacerbated by the increase in mineral surfaces and urban densification, thereby reducing cooling areas. An in-depth analysis of scientific literature reveals a gap in understanding UHIs in tropical contexts, highlighting the need to further explore existing solutions and their effectiveness in hot and humid climates.

In this paper, we present the results of an environmental study on the Urban Heat Island (UHI) effect at the district scale on Reunion Island. We couple an experimental field study, which involves deploying a large number of sensors throughout a neighborhood, with numerical modeling. The aim is to validate the Envi-Met software for predicting urban microclimate in hot and humid conditions. Envi-Met, a Computational Fluid Dynamics (CFD) tool, is employed in microclimate studies to create neighborhood-scale climate models by considering radiative and aerodynamic phenomena.

Our study focuses on a specific district on Reunion Island, leveraging a network of environmental sensors that densely measure thermal comfort parameters in urban areas. This district is modeled using Envi-Met alongside in situ measurements of air temperature, relative humidity, wind speed, and solar radiation. The model’s accuracy is validated against the sensor data collected at various times throughout the year, allowing us to assess the seasonality and temporality of UHI effects at this precise scale. Additionally, it enables us to evaluate thermal comfort and the distribution of heat within the district based on the urban form.

Once validated, these simulations will enable the prediction and optimization of thermal comfort for future neighborhood developments in tropical climates. Finally, the results of this work will contribute to validating a set of technical solutions aimed at mitigating UHIs by optimizing urban morphology, incorporating vegetation, and enhancing natural ventilation. This advancement will help consolidate an essential knowledge base for improving outdoor thermal comfort in cities in tropical regions such as Reunion Island.