sexta-feira, 28 de julho de 2017

Depave, a bright idea

As one removes the pavement, it is removed what was hiding the land, the natural support of life. As the land is uncovered, the green has its way to come back. Different dimensions of changes take place. Let’s consider some aspects of the question of depaving.

The sun rays incident on leaves are reflected more strongly than in the concrete. In other words, the albedo of the leaves is, in general, bigger than the albedo of the pavement (1). As a result, the leaves absorb less energy. The difference of albedo may be very important. When to pave is really imperious all attention should be given to the difference of albedo of the alternatives among types of pavement material. But when what matters is the difference of the albedo of leaves and the albedo of pavements, the differences of energy absorbed among alternative pavements are not so important as the different destination the leaves and the concrete or asphalt give to the solar energy absorbed. It as as comparing green roofs (2) and conventional or reflective roofs (3). The vegetables convert the solar energy absorbed in input for vital physical and chemical processes, including the photosynthesis. The construction materials, in an opposite way, convert in heat the solar energy absorbed. The pavement get heated and dissipate the heat in the surrounding air by convection and directly in the entire environment by increasing the emission of infrared rays. The air over the pavement gets heated, contributing to the tormentors urban heat island (UHI) effect. The air over green life, instead, contributes to alleviate the UHI (4).

To better the quality of life is good for all of us, and the green space is positively correlated with quality of life (5). This is a very important as the green is favourable to mental health (6). Being opposite to the pro depression pavement is a nice impact of depave, as more important as the number of depressed people is growing.

Unpaved land has the property of retaining and absorbing water. When it begins to rain the firsts rain drops that fall over the leaves tend to stay there. After the leaves become wet, the additional water flows. The land has a more proeminent benefical behavior. The firsts drops that fall on the land remains there instead of flowing. In the sequence the flow begins to be divided, part being absorbed by percolation, part flowing over the surface of the land. The flash floods are less intense as the water takes more time to begin flowing over the surface, and have a smaller flow. This property is invoked to determining the choice among types of pavement.

To those who the objective is solely to atenuate the flash floods, some poor solutions alternative to depave are satisfactory. The porous concretes that can percolate water are a kind of this type of solution. But changing the building material of pavement does not give the property of absorbing the solar energy incident not converting it in heat. It does not give the contribution to the mental health and the quality of life, it does not give contribution to alleviate the UHI. It is an action of Adaptation to Global Warming, by decreasing the impetus of flash floods. But it is an action inferior in results than maintaining the land.

If the mistake of paving what was not necessary is already done, Depave is the solution. Depave, a bright idea.


1 WANG, Shengyang (2015). Pavement albedo assessment: methods, aspects, and implication. Iowa State University. Digital Repository. Graduate Theses and Dissertations. Paper 14904. Avaiable at: Access July 13, 2017.

 2 Inovação e Adaptação ao Aquecimento Global. Green roof as an universal tool for Adaptation to Global Warming. Disposable at:
Access: July 14, 2017.

3 Inovação e Adaptação ao Aquecimento Global. A comparison between reflective and green roofs as tools for Adaptation to Global Warming.Avaiable at: Access: July 14, 2017.

4 YANG, Xiaoshan: ZHAO, Lihua (2016). Diurnal Thermal Behavior of Pavements, Vegetation, and Water Pond in a Hot-Humid City. Buildings, 6, 2; doi:10.3390/buildings6010002. Disposable at: Access: July 03, 2017.

5 Land Use Consultants (2004). Making the links: greenspace and quality of life. Scottish Natural Heritage Commissioned Report No. 060 (ROAME No.F03AB01). Avaiable at: Access: July 12, 2017.

6 TOWNSEND,  Mardie; WEERASURIYA, Rona (2010). Beyond Blue to Green: The benefits of contact with nature for mental health and well-being. Melbourne: Beyond Blue Limited. Avaiable at: Access: July 03, 2017.


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