;
;
Article authored by Tessa Brunette and Matthew Phillips
African cities are on the frontline of climate change, which is starkly clear in the increased frequency of both drought and flood events. Yet it is now widely understood that while cities across Africa are not the ones responsible for having caused global warming, they are the ones paying most dearly for it.
We have developed the Africa Sponge Cities Snapshot to get people talking about how cities across the continent can preserve and enhance their natural assets to increase their resilience to more frequent extreme weather events. The Snapshot reveals the current “sponginess”, or natural ability to absorb rainfall, of five diverse African cities: Cairo, Durban, Kigali, Lagos and Nairobi.
The results show that many of these cities have significant green and blue infrastructure – making them very “spongy”. But as they rapidly grow, African cities have an opportunity to leapfrog cities, particularly in the West – which during times of rapid growth have relied too heavily on carbon intensive grey solutions at the expense of nature. Cities have a major opportunity to shape future development so that it preserves and enhances their natural infrastructure, and in turn helps tackle increasing extreme rainfall events.
While Arup’s Global Sponge Cities Snapshot studied cities around the world, this report focuses on African cities. The urgency of the shared threat faced by these cities, and the scale of opportunity to enhance natural resources as they develop, means the concept of “sponginess” is especially pertinent.
All of the cities surveyed have a recent history of flooding. Durban saw extreme rainfall events in the order of 1 in 200-years in both April and May this year, killing over 450 people. At least 5 were killed in Cairo floods in March 2020 and 34 of Nigeria’s 36 states were hit by floods just in September, which killed 600 people and left 1.3 million displaced. In May 2020, over 280 people were killed in Kenya and over 810,000 displaced from floods which wreaked havoc across the country. This risk is only set to increase as climate change affects rain patterns. This will impact settlements old and new, formal and informal, that are located in at-risk areas.
When it comes to topography, there are notable differences between the cities surveyed – especially average rainfall, land use and soil type – although there are also many commonalities. In their own ways, all the cities surveyed have developed at pace in recent years. For most, policies and public funding have not matched rapid urbanisation, resulting in a lack of funding to build, maintain and upgrade infrastructure.
There are variations and notable examples of areas developing with more intentional design, but there needs to be a concerted effort from all aspects of government, the private sector and academia to turn thoughtful solutions into reality.
In Dar es Salaam, Arup is currently working with the World Bank on a Nature-based Solutions planning project to be implemented city-wide. Together, we are exploring how much green space, soft infrastructure and green corridors can help reduce flood risk in the city as it develops, as well as reducing heat island effects and improving biodiversity.
The results
Four of the cities surveyed receive over 1,000 mm rain per year and have fertile soil where vegetation thrives. The results reflect this, with Durban 40% “spongy”; Kigali 43% “spongy” Lagos 39% “spongy”; and Nairobi: 34% “spongy”. Cairo, by contrast, has a “sponginess” of 20%, which reflects the fact that its climate is not amenable to vegetation growth, on top of its high density of roads and buildings.
While the findings show that African cities are on the whole relatively “spongy”, especially when compared with cities previously surveyed, there are factors behind these numbers to consider. Many African cities experience high intensity rainfall events which result in flash flooding and cause damage. Most crucially, in many African cities, more than half of the population lives in informal settlements. This brings unique human, planning and design challenges, which must be factored into solutions. For example, many of these informal settlements are in particularly vulnerable locations, such as flood plains, close to rivers or even within stormwater dams, so approaches must be inclusive, sustainable, and robust.
Africa first solutions
Beyond “sponginess”, hyperlocal socio-economic factors should be at the centre of planning choices. For example, maintenance and repair must be low-cost and sustainable to account for budgetary restrictions and aligned with realistic long-term governance. This brings several benefits, one being that natural infrastructure maintenance can be a great source of local employment, in contrast with grey concrete-based flood management systems, which often require specialist engineering skillsets and don’t have multiple benefits.
Equally, Africa’s geography and land topography means that cities cannot go it alone. Joint international solutions are essential because Africa has many rivers and catchments that cross country borders. For example, the Nile brings rainfall from Uganda and Tanzania, some 6,600 km away, into Cairo. This means that the actions of a country upstream are often as important as a region’s own.
These waterways are clear opportunities for investment. In Durban, Arup is already engaged on various iconic commercial, industrial and residential developments, helping to deliver nature-based solutions at scale. eThekwini Municipality is also working to transform its 7,400 km of streams and rivers to better manage the impacts of climate change, such as flooding, through the establishment of the Transformative Riverine Management Programme (TRMP).
The Sponge Cities Snapshot aims to help stakeholders in African cities see their natural assets as an advantage and assess their value accordingly. This will empower them to deploy these assets to increase their city’s sponginess and support flood management, while also keeping local residents at the heart of decision-making.
Arup Africa Sponge Cities Snapshot: Full results
|
City |
Overall % "sponginess" |
Green-blue area |
Soil Classification and Run Off Potential |
|
Kigali |
43% |
67% |
High runoff potential (<50% sand and >40% clay) |
|
Durban |
40% |
59% |
Moderately-high runoff (<50% sand, 20-40% clay) |
|
Lagos |
39% |
58% |
Moderately-high runoff (<50% sand, 20-40% clay) |
|
Nairobi |
34% |
52% |
High runoff potential (<50% sand and >40% clay) |
|
Cairo |
20% |
29% |
Moderately-high runoff (<50% sand, 20-40% clay) |
[i] https://population.un.org/wup/publications/Files/WUP2018-Report.pdf
[ii] https://www.unesco.org/en/articles/being-able-predict-floods-will-save-lives-west-africa3
[iii] The World Bank’s Population living in slums (% of urban population) – Sub-Saharan Africa report (2018)