Call for sustainable planning amid African urbanisation boom

A seismic shift in the number of people living in cities across Africa by 2050 will require a focus on the creation of sustainable cities according to new research.

Using a new dataset, Rafael Prieto-Curiel of the Vienna based, Complexity Science Hub and colleagues analysed the coordinates and surface of 183 million buildings in nearly 6,000 cities across all 52 countries in Africa.

The study found that that if a city’s population doubles, the energy demand associated with commuting triples.

“Our model allows us to estimate African cities’ transport requirements and energy needs with a never before seen accuracy,” Prieto-Curiel, researcher at the Complexity Science Hub, explained.

Together with Jorge E. Patino from Universidad EAFIT and Brilé Anderson from OECD, the team measured the mean distance between buildings in 6,000 African cities and used it as a proxy for energy demand related to mobility. They chose Africa, cities in the continent are expected to grow faster than ever before in the coming three decades.

“Based on the distance between buildings, we calculated the expected distance and time to travel for every single person within a city,” Prieto-Curiel explained. Their result: double the population means triple the energy costs, as more people are forced to travel longer distances.

This tripling effect is due in part to urban morphology and how cities grow. “Constructing bigger buildings (area and height) near the city centre reduces the commuting distance, as well as the energy consumption of the city and helps preserve green spaces,” Prieto-Curiel added.

The team also found that big cities tend to be shaped differently than smaller cities. As they grow, larger cities tend to become slightly rounder and more compact. Smaller cities tend to have more of a sausage shape.

That shape also has an impact in the energy required to deliver the transport infrastructure.

“Imagine two cities that both have the same number of inhabitants,” the study said. “If one is round and compact, then objects and people are relatively close to each other. If the other one is shaped like a sausage, then some people must spend more time and energy to get from one side to the other. The problem with this is not only time, but also pollution. So a sausage-like city causes more pollution because of its shape.”

“Frequently, cities grow on the periphery as more housing is built in areas where the city is growing. This type of urban growth increases commuting distances and makes it more difficult to provide enough services for the new houses, such as sewage and electricity,” Prieto-Curiel said.

In many parts of the world extensive urbanisation has already taken place. In Africa, the next three decades will bring profound changes, the team said. Currently, cities like Cairo, Lagos, Luanda, Dar es Salaam, Nairobi and Addis Ababa are home to millions of people, and they are expected to increase their size considerably within the next decades.

“By 2050, Africa will have an additional 950 million people living in cities, up from 574 million people in 2015,” Prieto-Curiel continued. “More buildings – apartments, schools, hospitals, etc. – will have to be constructed.

“Where and how these new buildings are built matters greatly because today’s decisions will be with us for decades to come. And the resulting morphology of cities impacts permanently on a city’s energy needs.

“We should plan especially those cities that will grow extremely fast in the next twenty years with special consideration. They must be extremely resilient to many challenges.”

“Until now, we only had satellite images, but it was very difficult to manipulate these photos. Especially in smaller cities, it’s not so easy to identify what a building is,” Prieto-Curiel explained. Google AI’s new open access data set has changed that. Using a machine learning process, it can define the vertices of each building as coordinates. Like a city made of Lego bricks.

“Our results show that future energy needs for transport could be incredibly cumbersome if trends continue,” Prieto-Curiel said. “Designing compact, dense, and better-connected urban forms will help cities be more sustainable and liveable. Particularly in the case of African cities that will experience rapid growth within the next few decades.”