Population growth and a changing climate seriously threaten water security throughout the Mediterranean region. Important resource management decisions will be required but any such efforts will prove inconsequential unless reliable predictions can be made of the influence that changing conditions will have on the hydrologic cycle and available water reserves. By 2025 it is expected that 80 million Mediterranean people will face water shortage conditions (with less than 500 m3/ capita/year) and an inevitable consequence is that the percentage of unsustainable water supplies derived from fossil sources or from over-exploitation will rise. Under these circumstances, there is a risk that some fossil groundwater resources will become depleted and that coastal aquifers will be damaged by seawater intrusion. To achieve water security in the region, the challenge will be to:
• decrease water demand
• increase water supply, and
• use available water more efficiently.
Ultimately, there will be a need to develop management strategies that fully integrate groundwater and surface water, are holistic in approach and are based on sound scientific and socio-economic principles. In turn, this will demand a solid scientific database, reliable predictions of climate change, population growth and resource demand, and the judicious application of powerful computer codes capable of simulating both ground and surface water flow under transient conditions.
As the world's largest reserve of fresh, accessible water, groundwater, with its general resilience to drought  promises to play a crucial role in regions, such as the Mediterranean, where climate change threatens existing renewable resources. However, it is equally clear that despite the much touted merits of Integrated Water Resource Management (IWRM) , groundwater is often neglected, and the true benefits of managing groundwater and surface water resources conjunctively, will not emerge until the special and unique attributes of groundwater are adequately incorporated within IWRM. Time is of the essence as very little is known about the relationship between global climate change, sea level rise and groundwater resources. The types of question that need to be addressed are: (1) How will climate change affect the nature and seasonality of aquifer recharge? (2) How will fresh groundwater levels beneath coastal areas respond to changing sea/lake levels, and to what extent will rising sea levels promote the intrusion of seawater? (3) Will a decline in sea/lake level accelerate the release of contaminants stored in coastal aquifers to receiving water bodies? (4) Over what time frame will changes to the groundwater system occur?
Acknowledgements The work was supported by funding from the Natural Sciences and Engineering Research Council, Ottawa. I am grateful to Karina Howard for her editorial advice on the manuscript and assistance with the figures.
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