Forty-eight per cent of the population of the Western Indian Ocean Islands lives in urban areas. The least urbanized countries are Madagascar (30 per cent) and Comoros (33 per cent) (UNCHS 2001a). Seychelles is the most urbanized, at 63 per cent, followed by Mauritius at 41 per cent (UNCHS 2001a). Annual urban population growth rates in the sub-region in the past thirty years have ranged from one per cent in Mauritius to over five per cent in Comoros and Madagascar (UNDP 2000). Urban growth rates over the next 15 years are expected to average 2.8 per cent per year, ranging from 4.5 per cent in Madagascar and 4.1 per cent in Comoros to under 2 per cent in Mauritius and Seychelles (UNCHS 2001a).
The major factors encouraging rural-urban migration are the search for improved standards of living, employment and educational opportunities, and for access to communications and trade. In Mauritius, for example, economic growth averaged 7.7 per cent per year between 1985 and 1989 and 5.2 per cent per year between 1990 and 1999, with yearly growth in exports of 15.5 per cent and 6.4 per cent over the same periods (World Bank 2001a). The port and capital city, Port Louis, has facilitated this development through harbour operations, and, as a consequence, has attracted numerous industries. In Seychelles, 90 per cent of the population lives on the principle island of Mahe, with the majority (71 000 people) living in the capital Victoria where the country's main economic activity, tourism, is based.
The high rate of urbanization means that urban environments and infrastructure providers are under extreme pressure to deliver goods and services. In addition, many urban centres are located on the coast, where there are risks of environmental disturbance, erosion, and pollution. The large and growing number of tourists coming to the islands is also pushing up the demand for housing and infrastructure, and land is being reclaimed and coastal wetlands drained. In Seychelles, for example, coastal sand dunes are now being used for construction and land is being reclaimed from the sea with irreparable damage to the reefs, wetlands, marine and land eco-systems (UNEP 1999).
Data on adequacy of shelter are only available for Mauritius, where most residents are owners of their properties, and dwellings are of conventional type (UNCHS 2001c). The majority of towns and cities in the sub-region are growing faster than the provision of infrastructure and there are shortfalls in water supply, sanitation, waste disposal, roads and communications infrastructure, as well as in health and educational facilities. However, the Western Indian Ocean Islands fare better than many African countries, with all urban residents in Mauritius and nearly all in Comoros enjoying access to improved water and sanitation (WHO/UNICEF 2000). In Madagascar 85 per cent of the urban population has access to water supply and 70 per cent has access to some form of improved sanitation (WHO/UNICEF 2000).
Where these services are lacking, the urban population relies on septic tanks, and pit latrines. If not properly managed (especially in informal settlements) these can contaminate groundwater, and untreated domestic sewage-together with storm water run-off from impermeable surfaces in urban areas-can threaten drinking water supplies and the quality and safety of coastal waters. The result is a risk to biodiversity and human health from enhanced breeding and transmission of intestinal parasites, pests, and bacteria. Many of the urban developments-grown from villages and concentrated along the coastlines- discharge their liquid and solid wastes directly into the sea. For example, there are no waste management facilities in Comoros (UNEP 1998).