Abstract A numerical modelling approach has been developed to predict the vulnerability of aquifers to future climate change. This approach encompasses changes in recharge regime, dynamics of flow and storage patterns within aquifers, and natural hydrochemical changes. An application of the approach has been made to four hypothetical spring catchments representative of major carbonate aquifers in three European climatic zones. Since prolific carbonate aquifers typically combine a high transmissivity with a low specific yield, they can be expected to be more sensitive than clastic aquifers to changes in recharge patterns. Simulations of the study systems to the middle of the 21 st century predict different outcomes in the three different climate zones: (1) in the northern maritime zone (UK) recharge (and therefore discharge) is predicted to increase by as much as 21% in response to anticipated increases in precipitation; (2) in the continental zone (Germany) recharge in winter is predicted to remain approximately the same as at present, but summer recharge will decline dramatically (by as much as 32%), so that a net decrease in aquifer discharge is predicted; and (3) in the Mediterranean zone (Spain) recharge is predicted to decrease by as much as 16% of the present-day values. For all three systems, increases in water hardness in response to rising C0 2 are predicted, but are expected to be negligible in water resources terms.

Abstract In the framework of the PALAEAUX project, three coastal aquifers have been studied in Spain, looking at the possible existence of Pleistocene or Early Holocene fresh groundwater, in addition to the formerly studied Llobregat Delta. They constitute representative situations of the most common coastal aquifers. The main characteristics of these four areas are: The Llobregat Delta system, studied since 1965, is placed to the southwest of Barcelona (NE Mediterranean coast of the Iberian Peninsula). It is a sedimentary fluvial formation of Pleistocene to recent age, which is representative of small size coastal alluvial formations with the deep confined aquifer open to the sea offshore. Marine sea water penetrated the deep Pleistocene layer during the Flandrian sea-level rise but afterwards relatively high freshwater heads upstream allowed its progressive flushing to the sea through the submarine outlet since 6000–8000 a ago. Freshwater turnover time is shorter than the Holocene duration and it has been renovated due to natural discharge of the aquifer to the sea. The renovation process has recently been accelerated due to intensive groundwater exploitation during the past century. Nowadays, only freshwater a few centuries old remains in low permeability areas of the confined Pleistocene aquifer. The Doñana sedimentary aquifer system corresponds to the ancient estuary of the Guadalquivir River (SW Spain). It contains old saline groundwater that has not been flushed away due to the low freshwater head. In this aquifer 39 Ar, 85 Kr, 3 H, 14 C and 13 C measurements have been used to ascertain the age structure of several mixed groundwater samples. After correction, the oldest fresh groundwater 14 C age is c . 12–15 ka but 39 Ar ages point to somewhat younger water. Neither the stable isotope contents nor the recharge temperature calculated from noble gases show a climatic signature for these waters. The Inca-Sa Pobla carbonate system is the northeast sector of the island of Mallorca. Brackish and salt groundwater in the coastal area has been found along the coastal strip of S’Albufera, displaying what seems a convective-like flow pattern inside the up to 200 m thick aquifer. The most consistent estimated average 14 C ages of the mixed water vary between 9 and 13 ka, i.e. Early Holocene–Late Pleistocene. Water 18 O and 2 H contents do not show a clear climatic signature. The Amurga volcanic Massif is on the southeast of the island of Gran Canaria. Brackish groundwater is found in the thick phonolite rock sequence. The unsaturated zone can be up to 200 m thick. Groundwater salinity is due to recharge under arid conditions and the influence of marine airborne salts. Groundwater 14 C age is possibly c . 11 ka, indicating a Late Pleistocene age water mixture. The small recharge due to aridity and the thick unsaturated zone explains this. Stable-water isotopes show no clear climatic signature.

Abstract Coastal regions of Europe have special water supply problems due to the population pressure, competing demands and the ever-present risk of saline intrusion from modern and old sea water. This is especially the case in southern Europe where touristic demands exacerbate water supplies, often in semi-arid regions. Palaeowaters emplaced at times of lowered sea level offer potential high-quality, high-value reserves in many areas, although a lack of understanding of the nature of the resource, together with exploitation for non-drinking purposes and indiscriminate drilling, may already have damaged the underground reservoirs and the reserves within them. These aquifers may, however, offer sites that are attractive for seasonal water storage. Palaeowaters generally are of high quality and are demonstrably free of human impacts. Good drilling practice and operation are required to avoid contamination, the mixing of palaeowaters with more saline waters and avoidance of marine intrusion. Two case studies illustrating the management practice in areas containing palaeowaters – in the French Mediterranean coast and the Llobregat Delta area of Catalonia, Spain – are given. These demonstrate, above all, the need for integrated development, observation and planning, which involves all the stakeholders, especially the beneficiaries and end-users. There is a need for improved regulation for the protection, use and management of aquifers containing palaeowaters at both the national and European scale, to consider the intrinsic value of uncontaminated palaeowaters as a unique, non-renewable source of drinking water. The value of such aquifers for subsequent freshwater storage and also for use as a brackish water source for desalination may also be considered.