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The African coastal zone consists of a narrow, low-lying coastal belt. It also includes the continental shelf and coasts of 32 mainland countries. It is composed of a variety of ecosystems, including barrier/lagoons, deltas, mountains, wetlands, mangroves, coral reefs, and shelf zones. These ecosystems vary in width from a few hundred meters (in the Red Sea area) to more than 100 km, especially in the Niger and Nile deltas. In west Africa (Mauritania to Namibia), the coastal zone spans a broad range of habitats and biota and includes the pristine islands of Bijagos Archipelago; the offshore island nations of Cape Verde and São Tomé and Principe; and the remote central Atlantic islands of San Helena and Ascension.
A large percentage of west Africa's urban population lives in coastal cities. In Nigeria, for example, about 20 million people (22.6% of the national population) live along the coastal zone; about 4.5 million Senegalese (66.6% of the national population) live in the Dakar coastal area. About 90% of the industries in Senegal are located within the Dakar coastal zone. In Ghana, Benin, Togo, Sierra Leone, and Nigeria, most of the economic activities that form the backbone of the national economies are located within the coastal zone. Coastal areas also form the food basket of the region. Offshore and inshore areas, as well as estuaries and lagoons, support artisinal and industrial fisheries accounting for more than 75% of fishery landings in the region.
The coastal zone of east Africa, including coastal wetlands, extends from Sudan to South Africa and includes the near-shore islands off the coast of Tanzania and Mozambique and the oceanic islands of Madagascar, the Seychelles, Comoros, Mauritius, and Reunion. The desert margins of the Red Sea feature some of the richest coral reefs in the world. Coral reefs further south, extending from Kenya to the Tropic of Capricorn, are well distributed around most of the oceanic islands. They buffer the coastline against the impact of wave breakers and the full force of storms and cyclones. Many principal east African cities are located inland. Despite their low densities, however, coastal cities like Dar es Salaam and Mombasa are experiencing annual population growth of 6.75% and 5%, respectively (World Bank, 1995a). Coastal tourism and fisheries represent large inputs into the GNP of east African states.
Coastal population pressures and increasing exploitation of coastal resources-utilizing conflicting exploitation methods-have led to coastal degradation. Coastal erosion, flooding, pollution (air, water, land), deforestation, saltwater intrusion, and subsidence are some of the environmental problems degrading large parts of the coastal area of Africa. Coastal erosion already has been reported to reach 23-30 m annually in some parts of coastal west Africa (Ibe and Quelennac, 1989). In Cote d'Ivoire, high erosion rates have been reported in areas off the Abidjan harbor. It also is estimated that about 40% of the mangroves in Nigeria had been lost by 1980 (WRI, 1990); about 60% of mangrove areas in Senegal also have been lost as a result of mangrove clearing, coastal erosion, and increases in the salinity of water and soil. Industrial pollution from oil spills and discharge of domestic untreated wastes is polluting large areas of the coast, including lagoons and near-shore areas. The Korle lagoon in Accra, Lagos lagoon, and Ebrie lagoon in Abidjan all have been polluted, resulting in loss of fisheries resources.
Under doubled CO2, climate change is projected to adversely affect several physical, ecological/biological, and socioeconomic characteristics of the west African coastal zone and adjacent oceans that presently are under stress. At the same time, population pressures and conflicting policies of exploitation of coastal resources also have had adverse effects on coastal sustainability. Environmental problems degrading the coastal area are projected to increase as a result of either sea-level rise or an increase in extreme weather events (IPCC, 1996).
Climate change will exacerbate existing physical, ecological/biological, and socioeconomic stresses on the African coastal zone. Most existing studies focus on the extent to which rising sea level could inundate and erode low-lying areas or increase flooding caused by storm surges and intense rainstorms. The coastal nations of west and central Africa (e.g., Senegal, The Gambia, Sierra Leone, Nigeria, Cameroon, Gabon, Angola) have low-lying lagoonal coasts that are susceptible to erosion and hence are threatened by sea-level rise, particularly because most of the countries in this area have major and rapidly expanding cities on the coast (IPCC, 1996).
Africa's west coast often is buffeted by storm surges and currently is at risk from erosion, inundation, and extreme storm events. Inundation could be a significant concern (Awosika et al., 1992; Dennis et al., 1995; French et al., 1995; ICST, 1996; Jallow et al., 1996). Major cities such as Banjul (Jallow et al., 1996), Abidjan, Tabaou, Grand Bassam, Sassandra, San Pedro (ICST, 1996), Lagos, and Port Harcourt (Awosika et al., 1992)-all situated at sea level-would be very vulnerable. Finally, tidal waves, storm surges, and hazards also may increase and may modify littoral transport (Allersman and Tilsmans, 1993).
The coastal zone of east Africa also will be affected-although, unlike west Africa's Atlantic coast, this area experiences calm conditions through much of the year. Along the east coast of Africa, sea-level rise and climatic variation may decrease the attenuation of coral and patch reefs that have evolved along major sections of the continental shelf. The lessening of this buffer effect as a result of climate change would increase the potential for erosion of the east coast. Increases in population growth rates in the principal coastal cities of east Africa, combined with a likelihood of a 1-m sea-level rise, could create conditions for significant negative impacts on tourism-oriented economies, ecology, and natural habitats of this area.
Existing literature provides information about the implications of sea-level rise for Egypt, Nigeria, Senegal, Côte d'Ivoire, The Gambia, and Tanzania.
Results from studies on various aspects of the impacts and possible responses to sea-level rise on the Egyptian coast (Broadus et al., 1986; Milliman et al., 1989; Sestini, 1989; Ante, 1990; El-Raey, 1990; El-Sayed, 1991; Khafagy et al., 1992; Stanley and Warne, 1993) indicate that a sizable proportion of the northern part of the Nile delta will be lost to a combination of inundation and erosion, with consequent loss of agricultural land and urban areas. Furthermore, agricultural land losses will occur as a result of soil salinization (El-Raey et al., 1995).
Khafagy et al. (1992) estimate that for a 1-m sea-level rise, about 2,000 km2 of land in coastal areas of the lower Nile delta may be lost to inundation. Substantial erosion should be expected, possibly leading to land losses of as much as 100 km2. A very rough estimate of the agricultural land area that might become unusable is 1,000 km2 (100,000 ha). With an average land value of US$1.5/m2, the value of land loss in the lower Nile delta as a result of flooding alone will be on the order of US$750 million (2,500 million Egyptian pounds) (Khafagy et al., 1992). Outside the delta, erosion is expected to be quite limited. If average erosion were 20 m along 50% of the remaining coast (and assuming land values on the order of 5 Egyptian pounds per m2), the total loss would be about US$60 million (200 million Egyptian pounds).
For the Governorate of Alexandria, two main economic areas appear most vulnerable: the Alexandria lowlands and the Alexandria beaches (El-Raey et al., 1995). The Alexandria lowlands-on which the city of Alexandria originally developed-are vulnerable to inundation, waterlogging, increased flooding, and salinization under accelerated sea-level rise. The two surviving Alexandria beaches (Gleam and El Chatby) will be lost even with a 0.5-m rise in sea level. Based on the 0.5-m scenario, estimated losses of land, installations, and tourism will exceed US$32.5 billion. An average business loss is estimated at US$127 million/yr because most tourist facilities such as hotels, camps, and youth hotels are located within 200-300 m of the shoreline. It has been widely reported that 8 million people would be displaced in Egypt by a 1-m rise in sea level, assuming no protection and existing population levels (Broadus et al., 1986; Milliman et al., 1989). This estimate is based on the displacement of 4 million people in the Nile delta, as well as the entire population of Alexandria.
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