The sea advances and cities sink: African coasts at risk

Rising waters threaten the coasts and economic development of the Black Continent: the expansion of urban areas is also to blame

African coasts at risk: entire cities sink
Rising seas threaten the African coasts: the continent's population explosion among the risk factors (Photo: Landsat 8/NASA)

Il global sea level it is rising ever more rapidly: it is a process that began decades ago, triggered by rising temperatures, which it is now too late to stop. Climate projections predict that the sea will rise by 70 centimeters in a century, and the ones who will pay the price will be above all the coastal cities of Africa.

La demographic growth of enormous metropolises such as Lagos, Abidjan and Alexandria in Egypt (which in 2100, added together, will exceed 120 million inhabitants) can transform into a further serious risk factor: the overexploitation of groundwater can in fact cause phenomena of subsidence, that is, of land sinking, which combine with the advance of an increasingly warm and acidic sea.

And it's not just big cities that are at risk: according to a recent study, 20 percent of African historical-cultural heritage sites are already exposed to extreme coastal phenomena, and by 2050 the number of locations at risk will more than triple. Not only that: according to another research, the most serious danger concerns small towns of the west coast, which are destined for an unprecedented population explosion.

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A world map that simulates a six-metre sea rise developed by NASA: in the current scenario, the most threatened coasts are those of West Africa (Photo: NASA)

The coasts of Africa threatened by rising seas

THErising seas it is a phenomenon that scientists they have known and monitored for decades. Until the end of the 2s, growth was around 2013 millimeters per year; in the decade 2022-XNUMX it exceeded i 4,5 millimeters per year: a slow and inexorable response totemperature increase, which on the one hand cause the thermal expansion of water molecules and on the other cause the dissolution of polar ice caps and perennial ice reserves.

The advance of the sea involves coastal cities all over the world, but the most worrying scenario is that which concerns the coasts of Africa: on the continent with the highest population growth on the planet, theexpansion of cities it is already contributing to exacerbating coastal vulnerability.

Projections for 2100 predict that sea ​​level will rise by 70 centimetres globally: for Egypt, this will mean losing a large area of Nile Delta; for Lagos, which by the end of the century will be the largest city in the world, it could result in the forced transfer of a third of the population.

At the current rate, sea levels are expected to rise by 2030 centimeters directly by 30 almost 120 million Africans: if global warming is kept within +2°C compared to 1990 levels, we read in an article by the Africa Center for Strategic Studies, it could stop at 40 centimetres. But an increase in global temperatures of 4°C would lead to a rise of over a meter by the end of the century.

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The African coasts at risk
The Nile Delta is among the areas most at risk: it could lose kilometers of territory by the end of the century (Photo: Earth Science and Remote Sensing Unit, Lyndon B. Johnson Space Center)

Here there is the most intense population growth in the world

By 2030, the population of 7 largest coastal cities in Africa (Lagos, Luanda, Dar es Salaam, Alexandria, Abidjan, Cape Town and Casablanca) will grow by 40 percent compared to 2020 data, going from 48 to 69 million people: on a global level, explains the Africa Center for Strategic Studies, the coastal regions of Africa will record the highest rates of population growth and urbanization in the world.

As stated in the report “Foresight Africa: Top priorities for the Continent 2020-2030” by the US Research Institute Brookings, the African population located in low-altitude coastal areas (i.e. less than 10 meters above sea level) is growing faster than the rest of the world: within a few years, for example, more than half of Senegal's total population will reside in risk areas.

The rapid expansion of cities increasingly crowded and in need of infrastructure is further straining the stability of coastal areas: while sea levels rise in many of these cities the ground began to sink. Mombasa, Alexandria and Lomé are falling by approx one centimeter per year. The same thing happens in Lagos, Nigeria, which will exceed 20 million inhabitants by the end of the decade.

Recent research published in “Nature Communications Earth & Environment", in which scientists from European and African universities collaborated, analyzes the situation of the most populous coastal cities on the continent and identifies precisely in “unbridled” socioeconomic development one of the main risk factors for the near future.

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The town of Saint Louis, Senegal, has already been identified by the UN as the most at-risk area on the planet (Photo: Alweaver2/Wikipedia)

Anthropic subsidence: it is the invisible enemy of development

Cities can also sink due to anthropic pressure: the subsidence can be caused by overexploitation of the land. It happened with the Mekong Delta in Vietnam, and there are fears that the same could happen on the African coasts.

The study of Olusegun A. Dada, Rafael Almar and colleagues gives the example of St. Louis, a city in northern Senegal near the mouth of the river of the same name which is no more than 4 meters above sea level. The advance of the ocean and the floods have already forced the population of Saint-Louis, identified by the United Nations as the most threatened city from rising sea levels across Africa, to abandoning schools, mosques and homes.

Furthermore, the intrusion of salt water has radically altered the fishery in fresh waters and the agricultural production around the mouth of the river: a situation already experienced in some places in Ivory Coast, Ghana and Nigeria, and which could seriously hinder the socio-economic development of African countries.

As the study states, “Rapid population growth, migration to the coast, urbanization and unbridled and unregulated socioeconomic development expose more and more people and assets to rising sea levels, potentially also creating a human-induced subsidence".

A problem that mainly concerns the coastal countries of West Africa (Mauritania, Senegal, Gambia, Guinea-Bissau, Guinea, Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin and Nigeria): here, in fact, the very low altitude areas threatened by the sea, they already host a third of the population, and are destined to welcome more and more people.

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Green infrastructures to protect the coasts of the Black Continent

The effects of rising seas are dramatically widespread: in addition to storm surges and extreme events, with the intrusion of salt water into inhabited areas there is a risk of dangerous phenomena such as the erosion of roads and foundations and the flooding of septic wells, with consequent serious risks for the public health.

The advance of the sea could also erode the possibilities of development of African countries: just think about what it would mean, for a continent where 90 percent of import-export travels by sea, lose port infrastructure or see it seriously damaged.

To preserve the future coastal areas of West Africa, the study states, it is necessary to develop “a plan that includes relocation, an adaptation of urbanization that takes into account the risk of flooding and also of development limitations in high risk areas".

The good news is that they already exist virtuous experiences on the mitigation actions front: many African coastal cities have chosen natural and low-impact solutions such as restoration of mangroves, dunes, swamps and wetlands.

These are initiatives that have proven to be extremely effective, for example, during the passage of Cyclone Idai on the coasts of Mozambique in 2019. Here, thanks to the Coastal City Adaptation Project program, the restoration of the mangroves began in 2015.

Other examples of “green infrastructure” are the project “Management of Mangrove Forests from Senegal to Benin” and the “West Africa Coastal Areas Management Program”, a public-private program which intends to strengthen coastal habitat protection actions and which sees the participation of all the states of 'West Africa.

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Makoko, the shanty town on the outskirts of Lagos known as "the black Venice": the Nigerian coasts are among the most at risk (Photo: S.aderogba/Wikipedia)