WHYMAP and the World Map of Transboundary Aquifer Systems at the scale of 1 : 50 000 000 (Special Edition for the 4th World Water Forum, Mexico City, March 2006)

Introduction to the Worldwide Hydrogeological Mapping and Assessment Programme (WHYMAP)The availability of, and access to, fresh water is an important issue on the agenda of planners, politicians and executives all over the world.Although there seems to be an abundance of water in global calculations, surface and groundwater resources are increasingly under stress at regional and local scale.A vast majority of all freshwater is found in aquifers, many of them transboundary in extent.In the semi-arid and arid regions of the world, groundwater resources constitute the only reliable water resource for drinking water supply and irrigated food production.However, in spite of the sharply increasing use of aquifers in the past decades, the knowledge about the groundwater in aquifers and its management is still weak in many places.Investments in groundwater schemes are frequently founded on inadequate aquifer information in terms of quantitative data, reliable models and poor monitoring.In the last decades of the 20th century governments and funding agencies increased exploration for groundwater, due to water shortage problems at local and regional levels.Meanwhile the intensive use of groundwater by farmers for irrigated crop production has now placed groundwater resources under stress.To support sustainable management of aquifers, essential quantitative, national and transboundary information is needed to map, model and quantify the stored volume as well as the average annual replenishment; in addition, the chemistry of groundwater must be fully understood.Further, the vulnerability of groundwater resources to drought, over-abstraction and quality deterioration must be assessed, and the natural functions of groundwater for river runoff and ecosystems support safeguarded.