Partenariat Régional pour la
de la zone côtière et Marine en Afrique de l'Ouest
Climate change on the West Africa coastline
This Focus on climate change addresses three sections, as follows:
- Weather forecasts: consequences for the coastline environment and for marine and coastal biodiversity;
- Socio-economic consequences: fishery, agriculture, tourism, coastal infrastructures, urban development and health;
- Adaptation and mitigation measures.
What do weather experts foresee for West Africa in the future?
The magnitude of climate change will depend on whether measures are taken to reduce greenhouse gas emissions from human activities, particularly in countries of the North. Based on the models developed by IPCC experts, the following changes are expected in the West Africa sub-region: temperature rise from 3°C to 6°C by the end of the century or even earlier as shown by a few scenarios; reduced (from 20 to 35%) and irregular rainfall, and possibly a delay in the beginning of the rainy season; a higher frequency of extreme weather events (heat waves, rainstorms, violent winds); sea-level rise between 40 to 80 cm, which is likely to be higher locally depending on the significance of the tide, the strength of the wind or ocean swells triggered by storms off the coast. While these forecasts are relatively detailed for countries located north of the Gambia, such information is less specific for places further South when it comes to temperature and rainfall. The Sahel and West Africa are generally regarded as areas particularly sensitive to climate change.
Consequences for the coastline environment
It is still difficult to anticipate all the consequences of climate change as account should also be taken of the current effects of human activities. The most important aspects of these consequences, however, include sanilisation, which will affect agriculture and the quality of potable water along the coastline; reduced flow and drying up of rivers, leading to a shortage of freshwaters and potential conflicting interests; flooding in the coastal environment: on the assumption that the sea level rises above 1 metre, Saloum, the estuary of the Gambia, the cities of Nouakchott, Saint Louis and Banjul and seashore tourist facilities will be largely submerged. Floods will work havoc if associated with storm-triggered swells. Equally anticipated are an accelerated coastal erosion, whose effects are already perceptible, and ocean acidification. There are still uncertainties about the evolution of the Canary upwelling current. Most observation findings suggest that global warming has started since the 80s, entailing a change in the composition of species (which is positive in the case of round sardinella in the waters of Mauritania). The development of a synergy between water temperature and ocean acidification may have an effect on a number of biological processes.
Consequences for marine and coastal biodiversity
Ocean warming, a reality already measurable at 2,000 metres deep, causes tropical species to migrate to more temperate latitudes (i.e. northward from our sub-region) or to deeper and colder waters. A number of species may find it difficult to migrate in case of poor connectivity among their natural habitats. Inversely, larger species that are capable of travelling longer distances and that reproduce themselves in the deep sea will encounter less difficulty. If the size of the population of the species that cannot easily migrate to the north becomes very small as a result of overfishing, it will be more problematic for them to genetically adapt to the new environmental conditions and extinction may ensue. Feeding will become more challenging for fish-eating seabirds, such as Northern gannets and terns, if the water temperature compels fishes to remain in the depths. Climate warming will lead to an imbalance in the population of sea turtles whose gender at birth is determined by the temperature of the sand on laying beaches, indeed the higher the temperature the greater the chances to have female turtles. Difficult to control invasive species will grow, including jellyfishes and seaweed. It will be recalled that following the proliferation of seaweed in Sierra Leone in 2011, artisanal catches dropped by 40%.
The sea-level rise will affect coastal environments. In the face of this development, failure for the mangrove to move gradually upstream owing to a lack of space or the construction of coastal infrastructures will be synonymous with its extinction. This in turn will negatively impact the reproduction of fisheries (fishes, shrimps and oysters), wildlife (birds and manatees), carbon storage capacities and the coastline. However, it seems that a sea-level rise may benefit seagrass beds through the expansion of surfaces available on mudflats. Most of sandy small islands used by seabirds as a reproductive site will be submerged, as well as beaches where turtles lay eggs.
Ocean acidification will have negative repercussions on organisms with calcareous structures such as corals or shells, especially as these species cannot or can hardly move in search for better ecological conditions.