Experts propose solutions to heat island effect in African cities

Over the years, the colour of iron sheets in Uganda and most countries in Sub-Saharan Africa has changed from the reflective silver ones to darker shades such as red, blue, grey, maroon and green.

Whereas these may look stylish and beautiful, they do not mean well for our environment, especially now that climate change is taking its toll on the world in terms of temperature extremes.

Speaking to journalists from East and Central Africa during a virtual cross-border session recently, Mweetwa Mudenda, a public health expert from Lusaka Apex Medical University in Zambia, said roofing sheets that are dark in colour make buildings absorb a lot of heat during day and then release it into the environment during the night.

Such a cycle, Mudenda explained, worsens the heat island effect that has become common in Africa’s urban areas. As a result, urban areas remain hot during day and at night.

“We should avoid sheets that are dark because they absorb heat. We should instead consider the bright ones that reflect the heat in addition to adoption of good ventilation,” he said.

These, he said reflect the heat, making the structures cooler than they could have been with roofing sheets of dark shades.

What is the heat island effect?

The heat island effect is the phenomenon where urban areas experience higher temperatures than the rural areas that surround them.

This occurs because in urban areas surfaces like buildings, roads, and pavements absorb and retain more solar radiation/ heat than natural landscapes with vegetation, leading to a localised warming effect.

Environment experts warn that heat islands cause discomfort to communities and make houses inhabitable.

The heat island effect can exacerbate heat-related illnesses like heatstroke, especially for vulnerable populations, according to Mudenda.

He suggests that one of the best remedies for this problem is the return to the bright-coloured roofing sheets that dominated Africa before the 2000s. He also recommended the use of wall creepers.

“In the Netherlands, people are greening their walls with wall creepers, the plants that grow on concrete surfaces like a carpet. They are engineering those plants to grow on building surfaces to insulate them from heat,” he explained.

Mudenda explained that the adoption of plants that creep on walls and roofs also reduces the urban heat effect and has been successfully adopted in countries such as the Netherlands.

Moses Mugerwa, a civil engineer in Mukono municipality, agrees with Mudenda.

He says houses with dark shades of roofs worsen heat absorption, leading to discomfort and structural damage to buildings due to heat-related expansion and contraction of walls.

“Such roofs absorb the heat and transmit it through the walls, leading to expansion and contraction. This results in cracking of walls, especially in cases where concrete mixtures were compromised,” he says.

Mugerwa advises people to stick to the correct concrete mixture in order to min the integrity of their walls. He also advises Ugandans to consider living fences instead of concrete ones for health reasons.

“Living fences not only protect your home but also clean the air around your homestead. They absorb the bad gases and release oxygen, which is not the case with concrete fences. But you can turn a concrete fence into a living fence through the use of plants that spread on walls like a carpet. The wall eventually becomes green,” he explains.

About iron sheets with darker colours, Mugerwa says it will take a lot of effort to convince middle-class Ugandans to return to the silver-coured roofing sheets because they are considered cheap and old school.

“Most people prefer iron sheets in dark shades because of style. They want unique houses with unique colours. What saves them is that they build concrete ceilings to protect them from the heat of iron sheets. Otherwise, many would not be sleeping in those houses because of the heat. But in northern Uganda, the high temperatures have forced the population to stick to grass-thatched houses instead of iron sheets.

“In hot places like Yumbe, Gulu and Arua, the heat can force you out of your iron sheets house. That is why the adoption of iron sheets has been slow. Grass is good because it is biodegradable and isn’t one solid unit like concrete or iron sheets, which absorb and radiate the heat,” he explains.

The virtual session was organised by the Media for Environment, Science, Health and Agriculture (MESHA) from Kenya, and also featured speakers from Uganda, Zambia and Malawi. The major topic was climate change effects in urban areas. Among the issues raised were flooding, air pollution and disease outbreaks.

Brighton Aryampa, Ugandan Climate Advocate and Team Leader of Youths for Green Communities, rallied governments in the region to take the lead role in protecting the environment.

Dominic Naysulu, the national coordinator of the National Youth Network on Climate Change in Malawi, appealed to urban planners to integrate green infrastructure in planning.