This large asphalt surface, traffic, pollution and the lack of green spaces make cities react poorly to summer heat. Urban design shapes the microclimate where people live, and altering it can create conditions that help people cope better with high temperatures.
A tool to improve thermal comfort is bioclimatic urbanism. It considers sun and wind to design public spaces in cities such as streets and squares. Bioclimatic strategies combine three variables: wind, sunlight and humidity. In a big city, bioclimatic measures should include the following elements to fight heat:
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Shady areas during the central hours of the day.
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Spaces that create wind channels for breezes.
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Areas with fountains and layers of water.
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Areas with deciduous trees that provide high evaporation.
Adapt to both heat and cold
Beyond the heat waves of the summer of 2022, with record temperatures, it is also important to consider cold winter situations. Designing flexible strategies is essential.
In cities like Madrid, for example, there are months that are less warm than overheated, so it is important to allow sunlight on streets and squares in winter and shade in summer. High daytime temperatures can be offset by considering wind and evaporation.
Below are the main strategies for creating bioclimatic oases that improve summer conditions in the city.
1. Shading of streets and squares
During extreme heat emergencies, public spaces can be shaded by trees or by elements that provide shade, such as textiles along streets.
There is also the option to shade public spaces with pergolas or photovoltaic fabric canvases that add shade and the possibility of generating solar energy.
2. Wind in urban design
The first step is to take advantage of the wind patterns in the city during summer. Real time maps show wind speeds and directions, and data can be requested from meteorological institutions. In Madrid outskirts, wind speeds are higher than inside the city, ranging roughly from 3-4 km/h to 12-14 km/h. These charts help determine:
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Natural ventilation corridors if major streets carry the prevailing wind direction.
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Deciduous trees and shrubs placed in rows parallel to the summer winds to favor wind channels.
3. Increased vegetation in the city
Expanding park areas is key to improving the city’s thermal conditions in summer. With a wide selection of species adapted to urban climates, it is important to vary size and evapotranspiration characteristics.
For example, in Madrid, the city council has updated urban rules since 1997, including the concept of the green factor.
The green factor is a numerical parameter aimed at improving sustainability, thermal and bioclimatic comfort conditions and the urban environment of the city.
Calculating this indicator currently depends on the presence of vegetation on trees along streets, inside facades, on roofs and in public spaces.
4. Soil permeability
Sideswalks and driveways should be designed so that water can pass through easily, with near 90% permeability. The aim is to maximize permeable coatings. In Madrid, the minimum parameters are set by the City’s water management regulations.
The goal is to allow rainwater to seep into the soil. The final runoff is influenced by material composition, slope, precipitation and vegetation. One recommendation is to design sustainable drainage soils.
The aim is to increase street permeability and dampen heat, enabling runoff water to support vegetation growth and create a favorable microclimate.
5. The color of urban sidewalks
The color of surface materials matters for diffuse solar radiation and the thermal comfort of pedestrians. Generally, sidewalks and even driveways should use light colors, offering options beyond traditional asphalt.
The aim is to increase the albedo of horizontal surfaces on pavements and roads, reduce surface heating, and indirectly improve summer comfort conditions.
Thermal oasis in the city
The objective is to design urban thermal oases that create a suitable microclimate for as many days as possible.
All the strategies described here are combined: ponds and fountains are installed and deciduous trees are placed according to the prevailing summer wind direction to form wind channels. Light colored pavements and permeable surfaces cover at least 75% of total ground coverage.
Projections from the World Bank suggest seven out of ten people will live in urban areas by 2050. Adapting cities with bioclimatic strategies is essential in the face of increasingly common extreme weather due to climate change.
Source: Ecovant.