It is hot!
Global warming has detrimental effects on nature in general and thus also on us humans.
However, rising temperatures pose a direct danger to humans too, and not just in sub-saharan Africa but right here in the temperate zones.
In the EU, some 70% percent of the population live in cities or towns/suburbs, almost 40% live in cities.[02]
Exaggerating only slightly, cities can be seen as mountain ranges made of concrete.
The Heat Island effect
The concrete heats up depending on solar radiation and ambient temperature. As we know, the summers (and winters) are getting warmer,[03] and so do our cities.
This is known as the heat island effect and it most people will have experienced the fact that the city seems warmer than the surrounding countryside.
Many people flock out of the city during summer weekends in search of cooler places, such as a forest.
Heat waves are killing us
Heat waves put lives in danger. For instance, the World Health Organization (WHO) estimates that "in 2003, 70,000 people in Europe died as a result of the June-August event, in 2010, 56,000 excess deaths occurred during a 44-day heatwave in the Russian Federation."[05]
The heat exerts direct and indirect adverse effects on our health.
Direct effects are dehydration and heat strokes. Since heat lowers air quality, heat waves also leads to increased respiratory problems.
Indirect effects are psychological in nature such as reduced awareness resulting in accidents, but also societal such as an increased pressure on the health services. The heat also facilitates transmission of food- and waterborne diseases.
All these effects can lead to disruptions in our infrastructure (power and water supply), and transport facilities.
How to fight heat waves?
The obvious
The WHO advises to keep your home cool, to keep out of the sun (subject to occupational requirements), and to stay hydrated, in particular if you're elderly, very young, or infirm.
Seeing as we cannot all move to the country-side it is strongly advisable to build cities in such a way that they do not accumulate that much heat, however, that applies to new developments.
Roof garden: the solution?
The micro-climate of cities can be significantly improved by installing roof gardens, sometimes referred to as green roofs.
A building's roof that is partially or entirely covered with plants and a growing medium that is planted over a waterproofing membrane is referred to as a green roof or living roof. Additionally, it could have root barriers, drainage, and irrigation systems as additional layers.
Green roofs have many advantages.
They reduce reduce the heat island effect: In urban areas or other constructed environments with little natural vegetation, using green roofs might reduce the heat island effect, especially during the day.
They have a cooling effect: Green roof bind water and thus exert a cooling effect, and can cool the city's air by up to 5 degrees.
They improve air quality
They improve bodiversity: They provide a habitat for species, thus improve bio-diversity.
They sequester CO2: As terrestrial plant life depends on photo synthesis, they also sequester CO2.
It is true that the rate of carbon sequestration by grassland is not very high (approx. 0.2 - 1.5 kg m-2 year-1 [06]) and it won't make up for the CO2 released into the atmosphere by the forest fires that have plagued Europe (and other parts of the world) this summer but every little helps.
They improve human health: By limiting heat transfer through the building and by improving the quality of air
Energy savings: The primary advantage green roofs provide is the added insulation to the apartments or office spaces underneath and this effect is two-fold: In summer it provides a cooling effect and in winter it reduces the cost of heating.
Is it expensive?
Although green roofs initially cost more than conventional materials, building owners can help make up the difference by managing energy and stormwater costs more cheaply, and perhaps by taking advantage of the longer lifespan of green roofs than that of traditional roofing materials.
In conclusion, as with all approaches to mitigating climate change, the installation of green roofs is no silver bullet but it has a role to play in any holistic strategy.
Of course, not all roofs are suitable, in particular, flat roofs are more suited than sloped roofs.
Considering, however, the available area in many city centres there are significant gains to be had.
Many proponents of green roofs think one step and look at ways of greening up facades as well. This is sometimes known as vertical gardening (but that will be for another article).
If you would like to know more about environmental, social or economic sustainability, talk to the experts.
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[01] DOI:10.1016/S0140-6736(15)01156-3
[02] https://ec.europa.eu/eurostat/web/products-eurostat-news/-/EDN-20200207-1, last accessed 2022.05.24
[03] https://www.science-by-trianon.com/post/ipcc-report-2022-the-need-for-radical-changes, last accessed 2022.08.29
[04] https://commons.wikimedia.org/wiki/File:Urban_heat_island.svg#/media/File:Urban_heat_island.svg, last accessed 2023.01.24
[05] https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health, last accessed 2022.05.24
[06] https://www.d.umn.edu/~rmoen/docs/BMWR/Ch_13_Topic_1_Primary_Production_And_Forage_In_Different_Plant_Communities_5_32.pdf, last accessed 2022.08.29
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