How would you define the summer in your city? Often it’s a season with pleasant temperatures, for many this is a synonym of beaches, dresses and shorts. Nevertheless, I do believe that some of you would say that it is nothing but a living-inside-an-oven experience, especially those who live in big cities, strongly urbanised and located between the tropics (my city, Recife – also called Hellcife – is a pretty beautiful mix of all these things!). These characteristics, added to the temperature increase during this season, may cause an effect called thermal stress.
But what does it mean?
Thermal comfort can be defined as a condition of welfare and satisfaction with the environment temperature. This is a relative measure, because it is also related to each individual’s physiology features like sex, age and other variables. Although, it’s known that, for humans, this range of “comfort” varies between 19°C and 28°C. Temperatures up or above this are likely to create thermal stress. Well, as you can wonder, to feel like a popsicle is NOT cool. Much less feeling like a fried egg.
When we deal with high temperatures, our bodies work hard to maintain the homeostasis, spend much more energy and, obviously, we get moody, sweaty and sticky (eww).
With the rising and urbanisation of cities, this problem tends to increase due the lack of natural ventilation. These areas usually show high concentration of buildings with dozens of floors that act as wind barriers, huge regions of asphalted streets that are responsible for absorbing luminous energy and release heat to the air slowly, and also a low abundance of vegetation that implies in a higher solar incidence through the atmosphere down the cities and people.
Does this combination sound familiar to you? You bet! As a result, we have the so-called Urban Heat Islands, typically found in metropoles which basically refers to the heat storage in the lower layers of atmosphere, making the ‘big cities’ several degrees hotter than smaller cities and rural areas. In East China, studies show that up to 44% of surface warming is due to Urban Heat Island effect. Yes, we are inside a slow cooker.
Ok, but what thermal comfort and urban heat islands have to do with… trees? Everything!
- Trees perform a process known as evapotranspiration, cooling the leaf and adjacent air due to exchange of latent heat. The vegetation removes heat from the middle and transforms it instead of storing, and releases steam water. Double effect! In addition to temperature’s decrease, they help out the air to be moister – no more nosebleeds.
- They also have a low albedo (a luminous measure used in architecture) and, with this, the Sun rays are absorbed instead of reflected from the leaves’ surface.
- Their dense canopies also avoid high solar radiation to be in contact with the surface, acting as a ‘luminosity filter’.
- During photosynthesis, trees kidnap CO2 from atmosphere, decreasing the greenhouse effect.
- Besides all of this, they also have a high landscape value, making the environment much more enjoyable for living, walking and doing outside activities.
There are many studies around the world that confirms the influence of vegetation upon thermal comfort in urban areas. Some researches conducted in Brazil found differences of up to 5°C on the temperature between areas without vegetation coverage and areas near to parks, squares and malls located on the same city. Other studies have shown significant differences in the use of air conditioners during the Summer in similar situations (with and without vegetation), which means less energy usage (cheaper bills, yay!). But it is not (only) about the money, money, money… this is also about our future. By reducing our energy consumption, we are also walking, step by step, from a dependent and explorer model of society to a more sustainable, greener and healthier one.
So, have you ever heard about the phrase: “Every man should build a house, plant a tree and have a son”?
What about start by “planting a tree”?
Ps: Building a house and having a son… well, this is up to you.