If you have been into a conversation with others or overheard people saying Abuja is so hot, here are the best reasons why it is so. We may all think heat and its presence is caused by nature, the sun or the hot dry winds of the Sahara Desert. But they aren’t the only reasons why.
The biggest heat source, the sun, emits as much heat as it wants to, but other factors limit how much of this heat gets into our cities, how much is retained and how much is emitted back or outside the city.
Whenever each of us builds a house, he or she increases the amount of heat in that area and generally, the city. Whenever the city councils builds a road, a percentage of heat will be added in your city. It’s a straightforward heat budget, the more concrete buildings, asphaltic roads and developments we have in the city, the more heat that will be present in our city, especially at night.
Urban heat island (UHI), is a phenomenon in which urban areas have higher temperatures than nearby rural areas, due to human reasons. The phenomenon has been discovered about 50 years ago and is known to affect so many cities’ energy consumption, thermal comfort, air conditioning costs and human health . The more a city develops (puts up more buildings), the more heat island it builds.
I came to know about this phenomenon as a graduate student. My MSc thesis had chiefly investigated how to make our buildings cooler by using living green roofs (they inevitably cool the cities too). UHI is present in many cities in the world, albeit unwanted. Many cities are doing whatever they can to combat this effect. One major way is increase in vegetation; trees, green roofs, high albedo materials (materials with high solar reflectivity), water bodies and fountains, etc. So if we want to mitigate UHI, we need to combat it by growing vegetation.
What about Abuja?
Let’s understand a little of the geography of Abuja. At an elevation above sea level of 864m, the capital of Nigeria sits higher than many Nigerian cities. The climate is a tropical savannah, with above average temperatures of 25 degrees Celsius, rocky terrain and a rainfall season that lasts for only 5 months. There are many hills around the city. About 4 million people live in the city during the day time, with only a quarter of a million estimated to be living in city at night. It’s like the Bay area in the US. Owning to high costs of apartments and rents, many people who work in the city during the day time travel for 20 to 50 kilometres to their homes in nearby areas.
These nearby areas aren’t flooded with all the cars, concrete and asphalt of Abuja. As I earlier mentioned, concrete and asphalt are the major reasons why we have UHI.
Those materials and many others developers put, behave like heat sinks. During daytime, they absorb heat from the sun. When the night comes, instead of the city to be cooler, it is hot because the heat sinks emit this heat back in to the environment. As soon as the heating source disappears (they stop absorbing heat), they start re-emitting heat back.
If you really want to experience this, you should take a walk in your neighbourhood at night. You will feel the night is still warm, instead of it to be cool like the neighbouring rural areas with less built up areas. Placing your face very close to the road or interlocking blocks, you will most likely feel a hotter air around that region than when standing. This heat, summed up from all heat sinks in the city, causes the UHI.
So when you want to build tomorrow, ask your building engineer and architect to use non-heat sinks on your site. Don’t do interlocking blocks around your house, put grasses. Green vegetation, owning to their nature, do evapotranspiration. Evaporated water cools the microclimate around the house and ultimately, the city. It improves the thermal conditions of the city.
Mitigating UHI in Abuja
Its sad when you drive in to so many estates in Abuja with little or no vegetation at all. The urban planning and building policies have inevitably increased UHI. The policies must change to push for developers to start using high albedo materials. I blogged about the plans of enforcing green building strategies in Abuja by the development control here. But we do not only need green building regulations, we need city wide green regulations. More trees, more green areas, less concrete, less asphalt, more use of natural ventilation, more water bodies, etc. Building policies remain the biggest way to effect a big change on reducing the UHI present in our cities. As clients, developers and designers, we can equally be motivated by the need to make our city greener through the various ways we act.
Cooler cities meant cooler environments to live, less heat, less energy consumption, more energy costs savings, better health and thermal conditions etc. etc.
Has this piece broadened your horizon of how cities become hotter than rural areas? Do you wish to build a house or an estate and want to make it as green as possible? Why not get in contact with me.