Harnessing Urban Microclimate Simulations for Sustainable City Planning

In the heart of urban development lies the challenge of creating comfortable, livable spaces that not only foster social cohesion and promote a healthy lifestyle but also support the thriving of small businesses. Our recent project delved into the intricacies of urban microclimates, explicitly focusing on the urban heat island phenomenon—where city centres experience significantly higher temperatures than their rural surroundings, a common occurrence in metropolises like Tokyo, New York City, and Paris.

The Simulation Journey

Our journey began with the simulation of urban microclimates to understand the impact of extreme heat events and urban heat islands on neighbourhoods. The simulations were meticulously designed to provide scientific data for a 3D urban environment, which served multiple purposes:

• Guiding city planners and policymakers in establishing building and urban design standards for heat resilience.
• Offering data-driven insights for urban development to mitigate the effects of extreme heat.
• Validating new or existing urban designs for their effectiveness in improving thermal comfort.

The simulations were instrumental in recommending heat-resilient urban design strategies. These included strategically placing blue-green infrastructure, increasing the albedo of building exteriors and designing urban morphology to enhance natural ventilation—all aimed at improving outdoor comfort levels.

Leveraging Helsinki’s OpenData for Simulation

Our project showcased the potential of Helsinki’s OpenData in simulating urban microclimates. We utilised a wealth of data, from 3D building models to urban tree databases, to create a detailed simulation environment. This approach not only supported Helsinki’s Digital Twin initiative but also provided actionable data on urban microclimate variables.

The Building Blocks of Simulation

A comprehensive collection of data underpinned the simulation:

• 3D Building Models: Sourced from the Helsinki 3D+ portal, these models were refined to the necessary level of detail using advanced tools like Autodesk Civil 3D.
• Urban Tree Database: This provided the precise location of trees, enhancing the simulation’s accuracy.
• Zoned Green Areas: Green spaces were mapped out to assess their impact on the microclimate.
• Digital Elevation Model: This helped us understand the terrain’s influence on urban heat distribution.
• Weather Data: Historical weather data from the Finnish Meteorological Institute was crucial in defining the simulation period.
• Construction Materials: The physical properties of materials used in urban construction were factored into the simulation to predict their thermal behaviour accurately.

Simulation Software Suite: SOLENE-microclimat

Our tool of choice was SOLENE-microclimate, a cutting-edge suite developed by CRENAU, which allowed us to simulate the microclimate’s components—air temperature, solar exposure, and wind speed—over our 3D model.

The Three-Stage Simulation Process

1. Thermal Radiative Initialization: This sets the stage for the simulation by initialising the urban microclimate variables.
2. Computational Fluid Dynamics (CFD) Coupling: Here, the simulation came to life, integrating conductive, convective, and radiative energy flows.
3. Universal Thermal Climate Index (UTCI) Calculation: The final stage involved calculating the felt temperatures, providing a human-centric measure of thermal comfort.

Recommendations and Conclusions

Based on our simulations, we recommend the following for urban areas:

• Integrate Blue-Green Infrastructure: Properly placed vegetation and water bodies can significantly reduce heat accumulation.
• Optimise Albedo: Light-colored paints and materials for building exteriors can reflect solar energy, mitigating the urban heat island effect.
• Design for Ventilation: Urban layouts should promote natural wind flow to cool down neighbourhoods naturally.

Through this project, we have demonstrated that with the correct data and tools, urban microclimate simulations can be a cornerstone in designing cities that are not only resilient to heat but also promote a higher quality of urban life.