Availability of freshwater in the Western Indian Ocean islands is a priority issue, as a result of: variable rainfall and high run-off; increasing domestic, agricultural and industrial consumption; and a lack of storage capacity. Pollution from a variety of sources is contributing to restricted availability of water for human use, and is contributing to environmental degradation. Therefore, implementation of integrated water resource management strategies is a priority in the sub-region.
Access to freshwater in the islands of the Western Indian Ocean Islands is complicated not only by variability in rainfall, but also by disparities between the abundance of water and the distribution of the population. Only Madagascar has abundant internal freshwater resources: a total of 337 km3/yr (UNDP and others 2000). However, these resources are unevenly distributed across the country due to the terrain, and poor infrastructure development means that large sectors of the population, especially in rural and coastal areas, lack access to water. Mauritius has just 2.21 km3/yr, or 1 970m3/capita/yr, of freshwater, which is close to the water stress threshold of 1 700 m3/capita/yr (UNDP 1998). This poses a challenge for the supply of water to urban centres.
Although the climate in the Western Indian Ocean is humid maritime, most of the rainfall occurs during a few months-December to April. Therefore, many islands experience periods of water shortages. The southwest region of Madagascar is the driest part of the Western Indian Ocean Islands, and experiences periodic drought (UNEP 1999b). In addition, monsoon rainfall and cyclones are common, and much of the water is lost through run-off. Comoros has an almost complete absence of surface water, because of the high permeability of its soil (UNEP 1999b). Deforestation and the clearing of land has occurred in all the islands, and has contributed to high rates of run-off.
There are many rivers (92 in Mauritius alone), natural and human-made lakes, and considerable groundwater resources in Madagascar and Mauritius, although these have not been evaluated or exploited thoroughly (UNDP and others 2000, UNEP 1999b). Wetlands are also important habitats on all of the islands in the sub-region, providing breeding grounds for large numbers of waterfowl. However, these are coming under pressure for land development, especially in the smaller islands, where tourism and population growth are driving the demand for housing and industry. To date, Madagascar has declared two wetlands as Wetlands of International Importance under the Ramsar Convention, and Mauritius and Comoros have each designated one Ramsar site.
Data for total annual withdrawals are not available for Comoros or Seychelles but, in Madagascar and Mauritius, withdrawals by all sectors represent a small percentage of annual renewable resources (6 per cent and 16 per cent respectively) (UNDP and others 2000, UNEP 1999b). The agricultural sector is by far the greatest water user, accounting for 99 per cent of all withdrawals in Madagascar and 77 per cent in Mauritius (UNDP and others 2000, UNEP 1999b). This reflects the importance of agriculture in economic development and livelihood subsistence and, in Mauritius, particularly the production of sugar cane, yields of which are among the highest in the world (FAOSTAT 1995). The area under irrigation grew from 12 000 ha in 1970 to 17 500 ha in 1995, most of which was sugar cane (FAOSTAT 1995). In Seychelles, water is used to irrigate orchid farms, as well as food crops, in times of water shortages. Groundwater is largely used for this purpose, as it was on Mauritius until the costs of pumping became prohibitively high (FAOSTAT 1995).
Details of water consumption are not available for the sub-region. However, in Mauritius, the second largest user of freshwater is the domestic sector which accounts for 16 per cent of all withdrawals (UNEP 1999b). This is largely to support the other economic mainstay of Mauritius, namely, the tourism industry, and it has been supported by significant investment in water supply infrastructure. Consequently, 100 per cent of the population, in both rural and urban areas, has access to piped water and improved sanitation (WHO/UNICEF 2000). By comparison, only 47 per cent of the population in Madagascar has access to piped water (although, in urban areas, rates are as high as 85 per cent), and 70 per cent of urban poulations and 30 per cent of rural populations have access to improved sanitation (WHO/UNICEF 2000). In Comoros, only 33 per cent of people have safe sanitation (UNEP/COI 1997).
With growing populations, and expansions in tourism and other industrial sectors, the demand for freshwater is expected to increase over the next 25 years in all the Western Indian Ocean states. Supplies per capita in Mauritius are falling, and are predicted to be within water stress levels by 2025 (Johns Hopkins 1998). In Comoros, per capita annual water resources are expected to fall to 760 m3, creating a situation of water scarcity (UNDP 1998). In Seychelles, water shortages were so severe during 1998 (due in part to the El Niņo Southern Oscillation phenomenon) that brewing and fish canning industries were temporarily closed (UNEP 1999b). This had such an impact on the local economy that the government has since commissioned a water desalination plant, in order to augment supplies. Losses from old water pipes further compound problems of current and future supply, accounting for up to 50 per cent of domestic withdrawals in Mauritius alone (Government of Mauritius 1994). Low storage capacity by households and in the public system aggravates the situation (Government of Mauritius 1994). The dry spells and periodic droughts which are common in Mauritius force water rationing in the north of the island, and increase the risk of contamination through the infiltration of untreated surface water.
The islands of the Western Indian Ocean are extremely vulnerable to climate change, not only in terms of sea level rise and associated loss of land and infrastructure, but also in terms of reduced availability of freshwater. Potential inundation of groundwater aquifers could foreclose options to exploit these resources, and alterations in rainfall quantities and distribution patterns, together with temperature and evaporation changes, may also reduce surface water availability (IPCC 2001).
These conditions of water scarcity and stress will continue to restrict economic and social development in the sub-region through curtailment of industry, agriculture, tourism and subsistence, unless a dramatic shift in policy is made towards IWRM. Major challenges include: the shortage of freshwater; improvement in freshwater management; and balancing the competing demands of population, agriculture and tourism. At present, an adequate framework of integrated policy is lacking. Water pricing does not reflect the true cost of production and distribution, and the capital cost of increasing supply. Lack of sensitivity to water conservation by industrialists, tourists and local residents exacerbates the problem (UNEP 1999b). Therefore, the priority is demand management, through public awareness and education, as well as through economic incentives. Reforms to date in Mauritius include: the diversification of crops, away from the heavily irrigation-dependent sugar cane; and conversion to more efficient drip, pivot, guns and sprinklers. Localized irrigation from small impoundments is being encouraged, instead of reliance on large dams that incur higher evaporative losses (FAOSTAT 1995).
Seychelles is looking to increase its crop production through improved irrigation, but also through the use of hydroponics, a technique that is currently under development (FAOSTAT 1995).