Concluding remarks

The integrated analysis of geological and hydrogeo-logical data indicates that the Yperia Krini spring has little storage capacity and that it is very sensitive to rainfall variations. On the other hand, historical information indicates that important climatic changes have influenced the whole Mediterranean area in the past, affecting the Yperia Krini spring in such a way that the broader area suffered a strong social and political decline.

During the last few decades, the concomitance of a relatively dry period (i.e. low precipitation) affecting the Aegean region and the huge increase of cotton cultivation in large sectors of Thessaly, central Greece, has forced local people to search for new water resources to provide their needs. Accordingly, during the 1970s and 1980s, the synergy of the natural phenomenon with inappropriate agricultural choices was coupled with the drilling of a huge number of bore-holes across the entire region. These water-wells, which mainly exploit the alluvial multi-aquifer system of the Larissa Plain, caused a significant drop of the piezometric level (Fig. 10) that critically exceeded the capacity to regenerate the underground natural hydraulic conditions. As a consequence, a quantitative and sometimes qualitative degradation of the water resources occurred. The process was also associated with differential subsidence phenomena and ground fissuring that caused damage to structures and troubled the local people (Soulios 1997; Rapti-Caputo & Caputo 2004). The recent period of reduced rain suggests the occurrence of low discharge values for the next few years. Therefore, it is highly probable that the tendency to drill new wells to counteract the drought will further accelerate.

According to the scenarios of the Intergovernmental Panel on Climate Change (IPCC 2001a, b), an increase of the global surface temperature in the range of 1.7 to 4.0°C will occur by 2100, while the temporal and spatial behaviour of precipitation will be altered.

In particular, the average surface temperature in the Mediterranean area is expected to increase by 0.7-1.6°C per 1°C of global increase (Mitchell & Hulme 2000; Palutikof et al. 1996; Cubasch et al. 1996; Barrow et al. 1995; Palutikof & Wigley 1996; Karas 1998). According to most prediction models, it is expected that precipitation will decrease in several sectors of the Mediterranean area southern of latitude 40-45°N and will increase in areas north of 45°N (Giorgi & Fransisco 2000; IPCC 2001a; Palutikof et al. 1996).

Based on five climatic models, Mitchell & Hulme (2000) suggest that over the period 19902100 the mean temperature in Greece will increase from 3.1°C to 5.1°C with an average of 4.3°C. Changes in precipitation are more difficult to predict, since Greece is located in a transition climatic zone. Notwithstanding some differences, most models agree that precipitation will likely decrease during the summer months, while there is a larger probability that precipitation will increase in the northern Mediterranean sectors (ECSN 1995; Palutikof et al. 1996; Perissoratis et al. 1996; IPCC 2001a; Feidas & Lalas 2001).

As a consequence of (i) the structure of the spring and its small reserve, (ii) the possible future increase of temperature and (iii) the predicted decrease of precipitation, a decrease of the average spring discharge is to be expected, similar to what occurred in past centuries. Accordingly, the drilling of new bore-holes will not efficiently counter the impact of the reduced availability of water, while new strategies, such as rain harvesting, waste-water reuse and aquifer recharge, should be adopted to improve the exploitation of the underground resources.

We are indebted to M. Thanos, former geologist at the Y.E.B. of Larissa, for providing meteorological data of the pluviometric station of Sotirio. G. Soulios and G. Dimopoulos of Aristostotle University of Thessaloniki (Greece) provided facilities for the hydrochemical analyses and many fruitful discussions. Thanks to R. Caputo for discussions on the geological data. Useful comments and criticisms by two anonymous reviewer are also acknowledged.

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