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Sea-Level Rise and Impacts in Africa, 2000 to 2100. Application of the DIVA model to Africa.


Africa has a large and growing coastal population, including a number of important coastal cities. With sea-level rise, flooding and inundation of coastal areas would be expected to create problems for infrastructure, transportation, agriculture and water resources within the coastal zone.

While risks are not well understood, with 320 coastal cities (with more than 100,000 people) and nearly 56 million people (2005 estimate) living in low elevation (<10-m>

A review of the literature on global assessments and available national studies indicates that the continent is rapidly changing with a growing population and economy and strong trends of urbanisation. However, the continent remains poor, and is facing significant issues and potential problems associated with sea-level rise. The available global assessments on impacts of sea-level rise on deltas, wetland areas and port cities identify that Africa is highly vulnerable to sea-level rise and its consequences. However, the studies are not suitable for detailed synthesis. The review also shows that the lack of data is a major barrier for a better analysis. This includes information on present rates of sea-level rise and systematic coastal geomorphology of Africa’s coast.

In the absence of a bottom up synthesis, a range of scenarios were explored in Africa using the global DIVA (Dynamic Interactive Vulnerability Assessment) model. These included four scenarios of sea level (a global rise of 0.17m to 1.26m from 1995 to 2100) which were examined in conjunction with three socio-economic scenarios describing population density and GDP (A1FI, A1B and B1) for 33 African countries and 7 island nations/territories around Africa. Impacts were determined with and without adaptation, so that the benefits and costs of protection could be considered. These adaptation measures were the construction and increase in height of flood defence dikes to manage flooding, and beach nourishment to manage erosion. Beach nourishment is based on cost-benefit analysis, while the dikes were based on a demand for safety function which is applied depending on population density. Selected impacts have been reported in the years 2000, 2025, 2030, 2050, 2075 and 2100 (see Appendices 1 and 2). Five parameters were selected for detailed study: (1) People actually flooded, (2) Cumulative forced migration, (3) Loss of wetland value, (4) Total residual damage costs, and (5) Total adaptation costs. As well as Africa as a whole, countries were ranked according to the magnitude of impacts in 2030 and 2100

The DIVA analysis shows that whilst Africa is not the most exposed region in the world compared with east, south east and south Asia, sea-level rise still poses a significant threat. With a large and growing population in the coastal zone and a low adaptive capacity due to low national wealth and other development indicators, most African countries appear to be highly vulnerable. Without adaptation, the physical, human and financial impacts will be significant. On an African scale, for the A1B mid-range scenario (a 43-cm rise) approximately 16 million people will be flooded per year in 2100, 10 million people will be forced to migrate from 2000 to 2100, and there will be a total damage cost of US$38 billions per year in 2100. However, when adaptation is applied, these impacts can be significantly reduced at an annual cost of US$2.2 billion in 2100. With adaptation, the numbers of people that could be flooded are about two orders of magnitude lower at 17,000 people per year in 2100, while the number of people forced to migrate from 2000 to 2100 would only be 14,000. Similarly, residual damage cost could be reduced about one order of magnitude to US$1.1 billion when adaptation measures are considered. However, delivering such adaptation will be more costly and difficult than the headline cost suggests as the DIVA analysis is incomplete. This reflects several factors which are not well quantified: (1) the adaptation costs are incomplete, (2) the large adaptation deficit, reflecting that Africa is poorly adapted to today’s climate, and (3) the low adaptive capacity.

Considering the national results, countries can be ranked by their relative impacts and costs. These rankings provide useful insight on those countries that are most vulnerable. In absolute terms, several countries consistently appear in the top ten rankings. For people-based impacts concerning flooding and forced migration they are Mozambique, Cameroon, Tanzania, Morocco and Egypt. For economic damages they are Algeria, Egypt, Morocco, South Africa, Tunisia, Libya and Cameroon who are all estimated to have more than US$1 billion of additional damage per year under the A1B mid-range scenario in 2100. In absolute terms, the highest adaptation costs occur in Mozambique, Guinea, Nigeria, Guinea-Bissau and South Africa.

It is also important to note that sea-level rise will not be the only factor shaping Africa’s coast in the 21st Century. Other climate change impacts such as increased storminess, higher temperatures and reduced precipitation also have immediate or secondary impacts of the coast. These have not been considered in this study, but could have important effects such as more intense tropical storms hitting the coast of East Africa (Mozambique, Tanzania, Madagascar). In addition to climate change, there are many anthropogenic factors influencing the coast, such as the conversion of wetland to agriculture uses or the reduction of sediment and water fluxes to deltas, often combined with enhanced subsidence. While these factors were not considered here due to lack of data, they should be considered in future studies.

The issue of sea-level rise and Africa requires further research, including improving these analyses and more detailed studies that look at impacts and adaptation in more detail. In particular, given the importance of the Development Aid in Africa, the implications for coastal areas needs to carefully considered in the light of sea-level rise

Suggested citation

Brown, S., Kebede, A.S., and Nicholls, R.J. (2011).Sea-Level Rise and Impacts in Africa, 2000 to 2100. University of Southampton, UK, 215pp

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