UN launches first-ever global aquifer map

Posted: 27 October 2008

A worldwide map of ground water resources crossing national boundaries has just been published by UNESCO.

Almost 96 per cent of the planet's freshwater resources are found in underground aquifers, most of which straddle national boundaries.

Global aquifer map
Global aquifer map
Detail of UNESCO's global aquifer map. Click on image for full-size version. Click here for a legend to the map.
What the UNESCO map reveals is just how many aquifers cross international borders. So far, the organisation has identified 273 trans-boundary aquifers: 68 in the Americas, 38 in Africa, 155 in Eastern and Western Europe and 12 in Asia.Each trans-boundary aquifer holds the potential for international conflict - if two countries share an aquifer, pumping in one country will affect its neighbour's water supply.

The map is the culmination of eight years of research and development of an extensive ground water database by UNESCO's International Hydrological Programme (IHP).

Despite its strategic importance, no global inventory of this resource had been compiled to date. The detailed map of transboundary aquifers - available online - also indicates water quality of the aquifers, recharge of the aquifers, streams and rivers in the region of the aquifers, and population density near the aquifers.

The aquifers, which contain 100 times the volume of fresh water that is to be found on the Earth's surface, already supply a sizeable proportion of our needs. The growth in the demand for water since the second half of the 20th century has been met by the increased use of underground resources. Globally, 65 per cent of this utilization is devoted to irrigation, 25 per cent to the supply of drinking water and 10 per cent to industry.

Massive amounts of water are usedto irrigate cropland in California© Inga Spence/Holt Studios International
Massive amounts of water are usedto irrigate cropland in California© Inga Spence/Holt Studios International
Massive amounts of water are usedto irrigate cropland in California© Inga Spence/Holt Studios International
Underground aquifers account for more than 70 per cent of the water used in the European Union, and are often one of the only - if not the only - source of supply in arid and semi-arid zones (100 per cent in Saudi Arabia and Malta, 95 per cent in Tunisia and 75 per cent in Morocco). Irrigation systems in many countries depend very largely on groundwater resources (90 per cent in Libya, 89 per cent in India, 84 per cent in South Africa and 80 per cent in Spain).

Although aquifer systems exist in all continents, not all of them are renewable. For example, those in north Africa and the Arabian peninsula were formed more than 10,000 years ago when the climate was more humid and are no longer replenished. In some regions, even if the aquifers are renewable - being fed on a regular basis by rainfall - they are in some cases endangered by over-exploitation or pollution. In the small islands and coastal zones of the Mediterranean, populations often use groundwater more rapidly than it is replenished.

The aquifers in Africa, however, which are some of the biggest in the world, are still largely under-exploited. They have considerable potential, provided that their resources are managed on a sustainable basis. Since they generally extend across several State boundaries, their exploitation presupposes agreed management mechanisms in order, for example, to prevent pollution or over-exploitation by particular States.

Mechanisms of this kind have begun to emerge in recent years. For example, in the 1990s Chad, Egypt, Libya and Sudan established a joint authority to manage the Nubian aquifer system in a concerted manner. In their project concerning the Iullemeden aquifer, Niger, Nigeria and Mali approved in principle a consultative mechanism for administering the aquifer system. But such mechanisms are the exception.

The draft Convention on transboundary aquifers, prepared by the United Nations International Law Commission with the assistance of experts from UNESCO's International Hydrological Programme (IHP), is therefore intended to fill a gap in the law. The text which was submitted to the General Assembly of the United Nations on 27 October, calls on aquifer States not to harm existing aquifers, to cooperate and to prevent and control their pollution.