The 24th and 25th November 2008, the Catalan Institute for Water Research (ICRA) together with the Catalan Water Agency (ACA), organized a conference entitled Water Scarcity and management under Mediterranean climate. The regions included in the Mediterranean basin are amongst the world areas most suffering of irregular water supply and rising water demands.  Ultimately, this shortage of available water may not only have effects on water quality, but also on the ecosystems’ integrity, and may result in economic and social disarrangements. The meeting gathered more than 50 qualified experts in the different aspects of the water cycle to discuss on these issues. In addition to proposing immediate steps which can be acted upon by the public administration and companies managing water resources, the meeting aimed to define the most integrative needs for research which should be followed in studying the improvement of natural system and resource management.
 
Water scarcity occurs when water demand exceeds available water resources under sustainable conditions. Water scarcity and droughts have increased in number and intensity in the European Union, and it is foreseen that these conditions will increase with climate change. Of particular concern, evidence suggests that these changes could be especially pronounced in the Mediterranean basin. One of the most widespread droughts in NE Spain occurred in 2007-8, with an extremely high societal, economical and environmental cost. The problems observed in the Mediterranean basin are analogous to those in other areas (e.g. California, Australia), but also in some usually water-rich areas that will probably experience similar problems in the future. Recent trends show a significant extension of water scarcity across Europe.
 
Understanding water scarcity and the way to cope with scarcity is not just a matter for water managers or scientists. Water scarcity has a direct impact on citizens and economic sectors that use and depend on water, such as agriculture, tourism, industry, energy and transport. Water scarcity and droughts also have broader impacts on natural resources at large, through negative side-effects on biodiversity, water quality, increased risks of forest fires and soil impoverishment.
 
 
The analyzed trends in Catalonia indicate that water demands are close to available water resources. In spite of uncertainty of estimates, it is likely that available water resources will decrease in the medium and longer term. Episodes of low rainfall will extend in duration, and the frequency of intense rainfall events also will be greater. Land use has changed and will continue to change in the future. Higher forest cover, continuing sprawling of human settlements and rising economic activities (tourism, agricultural irrigation) are the main drivers for increasing water use
 
The increased pressure on water resources will cause additional effects on aquatic ecosystems, with some direct and indirect effects. This is particularly relevant since freshwater ecosystems deliver relevant services to human societies. The effects on watersheds are commonly focused upon streams and rivers. Hence there will be affects on morphology (incision, channel simplification), chemistry (higher nutrient and pollutant concentrations) and biological communities (lower diversity, arrival of invasive species, lower efficiency of biological processes). Regional climate models provide a series of consistent high resolution scenarios for several climate variables across Europe. Analyses in Mediterranean watersheds consistently suggest that the climate will be significantly hotter and drier, especially in summer. It is foreseen that this will influence both the fate and behavior of pollutants.
 
Analyzing potential alternatives and needs indicates that there is not a single and easy solution for water scarcity because multiple causes (or stressors) require multiple solutions. Several options need to be applied when considering the existing resources. In particular for the scenario of climate change, increased demand and decreasing resources must be considered. These options need to consider the delicate coupling between social and natural systems, where each has their share. Both improved technologies and upgraded water management practices are necessary in all sectors where water is used (e.g. agriculture, manufacturing or tourism). It is essential that the full economic and environmental costs be considered in evaluating the alternatives, where conservation of resources and their quality at the source could also be included. The use of decision support systems may be helpful in integrating the multiple actors, as well as in optimizing drought management and mitigation measures.
 
• Working for a culture of water-saving and efficiency is essential. This requires an active public awareness from citizens and economic sectors. Potential savings can be stabilized into the future and these savings extended to domestic and agricultural needs. Developing water savings in irrigation, within general planning for the economical needs of the whole territory, is essential.
 
• Valuing ecosystem services can provide a framework for understanding that societal needs and natural capital are not separated. Public education is critical to achieve the goal of compatible use of water resources and the conservation of our natural heritage.
 
• Desalination is a current option to obtain water resources that could provide a source of water (80 Mm3 in 2009 in Catalonia), that could be considered as independent of potential changes in climate. However, energy needs and costs are high. Consequently, desalination should not be considered the only option.
 
• Reuse of sewage waters can be considered as an adequate water source for urban, tourism and agricultural uses. With proper treatment, sewage water can even be used for drinking water. There exist several techniques adequate for the improvement of chemical and microbiological quality that could help to provide these uses. The solutions are linked, however, to available energy; this sometimes becomes the critical limitation. Public perception also needs to be improved when this source of water is considered. It is expected that 190 Mm3 of reused waters could be available by 2015 in Catalonia.
 
• Use of ground waters requires adequate protection of aquifers. Overexploited aquifers affect available water for surficial aquatic ecosystems and may create problems of subsidence and salt water intrusion. Recharging aquifers requires good chemical and microbiological quality of the waters. Some techniques to improve the water quality of underground waters exist, even at the large scale. Recovered ground water wells can provide additional resources (up to 25 Mm3 in Catalonia which could be raised to 90 Mm3 during extreme droughts).