The problem of heat bubbles in heavily concreted cities requires effective technical-political responses

The increasingly hot summers are bringing, especially in the cities, a very high and distributed level of temperature, not only during the during the day, but also during the night, making life unlivable for citizens.

Urban planning and urban heat

The urbanization of historic cities has seen the growth of housing buildings and commercial activities in increasingly close together nuclei

b>, eroding the green fabric to make way for continuous overbuilding.

In addition to the construction of buildings, even large ones and very close to each other, if even in a sort of building continuity, provision was made to pave the roads, car parks and connecting areas between one complex and another, with waterproof and heat-absorbing elements such as asphalt.

In a context of climate change, where heat waves hit population centers hard, today's urban planning and construction typology is completely inadequate to mitigate extreme phenomena .

Streets and buildings are charged with heat during the day, only to return it in all its vehemence in the evening hours, preventing a respite from heat to sunset.

The design of solutions to these problems sees the need to reduce the impervious areas that retain and release heat, such as asphalt depaving or continuous road coverings, to increase green areas, draining surfaces in order to mitigate the effect of heat accumulation.

What is urban depaving

Urban depaving is a concept that concerns the removal of pavements in urban areas for specific purposes.

The main objective of this practice is to redevelop urban spaces to improve people's quality of life, increase environmental sustainability and create more pleasant and functional areas for the community.

This process can involve several actions:

• Removal of asphalt or concrete pavements, such as, streets, parking lots and squares that are covered by asphalt or concrete. The work involves the removal of these hard and impervious surfaces, returning the area to a more natural and permeable state.

• The removal of these superstructures can be used to create parks, gardens and green spaces in previously paved areas. These spaces can support biodiversity, improve air quality and provide a healthier environment for city dwellers.

• The Removing waterproof paving can help prevent flooding and improve rainwater drainage, allowing it to be absorbed into the ground and recharge aquifers.

• Moreover, waterproof surfaces absorb and retain heat, contributing to the effect known as the"urban heat island" . By removing some continuous and waterproof paving, it is possible to improve the thermal comfort of urban areas.

How to solve the problem of urban heat islands

The problem ofurban heat islands can be addressed by adopting different strategies, among which urban depaving plays a role important. There are several aspects to address to encourage this phenomenon:

• Removing parts of pavement and replacing them with green spaces, such as parks, gardens and tree-lined areas, can help reduce the heat accumulation in cities. Green surfaces absorb less heat than concrete and asphalt, providing a cooler environment.

• Using vegetal covers on buildings (green roofs) or materials with low thermal capacity (cool roofs) can reduce the absorb heat and help cool buildings and surrounding areas.

• Promoting sustainable mobility by reducing vehicular traffic and creating pedestrian areas and cycle paths can reduce heat emissions generated by vehicles and reduce the heat island effect.

• Urban planning decisions can influence the intensity of the heat island. For example, increasing the density of buildings and reducing open spaces can increase the heat island effect, while careful planning can promote better air circulation and a greater presence of green areas.
• Using lighter, more reflective materials for flooringand roofing can help reduce heat absorption. At the same time, promoting permeable surfaces can facilitate stormwater drainage and reduce overheating.
• Furthermore, some cities are experimenting with urban cooling systems, such as the use of recycled water or evaporative cooling systems to reduce temperatures in densely populated areas.
• Finally, it is possible to protect and expand the surrounding natural areas, helping to maintain a more favorable microclimate and reduce the impact of urbanization on warming.




Why waterproof floors absorb and release heat more than permeable ones

Impermeable and permeable pavements influence the urban heat island effect significantly. Let's see how they work and what the differences are between these two types of flooring:

Waterproof Flooring

Impermeable pavements, such as asphalt and concrete, have a low capacity to absorb water. When the sun hits these surfaces, they heat up considerably, absorbing heat and accumulating it.

As a result, during hot days, these surfaces can become extremely hot, contributing to the urban heat island heating effect.

Moreover, rainwater flows rapidly on waterproof pavements, accumulating in a limited way and creating flooding and drainage problems in cities.

Permeable Paving

Permeable pavements, such as porphyry pavement, porous bricks, porous concrete, plastic and concrete gratings and many other products, allow water to penetrate through their surface and reach the soil below.

This type of paving has a higher drainage capacity than waterproof paving, allowing rainwater to be absorbed into the ground, recharging aquifers and reducing the risk of flooding.

Furthermore, permeable paving reflects less heat than waterproof paving, as the water on the surface evaporates and cools the surrounding environment.

Reduction of Urban Heat

Impervious paving contributes to the warming effect of urban heat islands, while permeable paving can help reduce it.

The presence of permeable paving increases the amount of water evaporation and promotes better air circulation, helping to cool the surrounding environment. Furthermore, green areas, such as parks and gardens, which often include permeable paving, further contribute to reducing urban heat through the process of plant transpiration and shading.




What are the most important urban depaving projects

Not many large-scale urban depaving projects exist yet, but there have been some interesting pilot projects and local initiatives.

Here are some examples of significant urban depaving projects:

Depave project Portland, Oregon, USA

The Depave project focuses on removing impervious pavements to create green spaces in urban areas of Portland. The initiative aims to create parks and gardens, as well as prevent flooding and protect the local ecosystem.

Sponge City project – China

Sponge Cities are a project tested in several Chinese cities, such as Shanghai and Chengdu, to address flooding and water management problems. These projects incorporate urban depaving through the use of permeable pavements, green areas and rainwater collection systems to prevent flooding and improve water resource management.

Green Infrastructure Project - European Cities

Several European cities are implementing green infrastructure projects that include urban depaving. For example, Copenhagen in Denmark has created cycle paths, green areas and parks on former car parks and asphalt roads to promote a more sustainable lifestyle and reduce the impact of heat islands.

Raining Street Project - Tokyo, Japan

In Tokyo, the "Raining Street" project was launched which aims to promote the use of rainwater for different purposes, such as urban cooling and irrigation. This includes depaving some areas to allow rainwater to drain and reuse.

Urban Heat Islands project - Melbourne, Australia

Melbourne has launched several initiatives to address the effects of urban heat islands, including depaving to create green spaces and cycle paths and use of materials with low thermal capacity for building roofs.

Growsmart Project - Boston, Massachusetts, USA

Growsmart is an urban depaving program launched in Boston to transform former parking lots and paved spaces into parks and public green areas. The initiative aims to improve the quality of life, health and sustainability of the city.