It is worldwide recognized and accepted that, in Southern Europe and the Mediterranean area in the last hundred years, the atmospheric temperature has risen by about 1°C, accompanied by a general decrease in precipitation. The trends detected in historical thermo-pluviometric series recorded in South/Central Italy show a general decrease in precipitation on an annual scale and a concentration of negative trends in the months from October to March. Analysis of the Standard Precipitation Index for the period 1951-2008 indicates higher frequency and duration of droughts in the last two decades: four prolonged dry periods (each lasting for up to three years) have been recorded since 1988, whereas only two main droughts have been identified in the four decades between 1951 and 1988. Climate change greatly influences the hydrogeological processes regulating both groundwater and surface water availability. If the present trends should continue, a total yield of 10-20% less than at present should be expected in the next 50 years. This work analyses the response of springs fed by karst/fractured limestone aquifers, extensively outcropping in Central Italy, taken as representative region, to climatic variations. It is shown how groundwater regime, the discharge of springs and their response to climate change depend to a great extent on the geologic and structural setting of the system. Some of the examined springs are “local systems” which represent “overflow” of a “deeper regional flow” feeding larger “base springs”, often of poor quality (salty water), due to interactions with evaporite sediments of Triassic age. A dynamic groundwater divide, the position of which is greatly influenced by climate change, separates the recharge areas of base springs from those of local springs: as the piezometric surface is lowered, the watershed moves towards systems located at higher altitudes, producing a reduction in their recharge areas. Therefore, local springs connected to a base flow are more vulnerable to climate change than springs with recharge areas which do not feed a deep regional flow. The Bagnara and Lupa springs, taken as examples, have recharge areas with similar lithological, topographical and climate characteristics and similar mean discharges (about 120 l/s). In spite of this, only the discharge of the Bagnara spring, which is connected to a regional flow, fell dramatically during recent prolonged drought periods (e.g., 2001-2003 and 2006-2007). The results of the present research may be useful in studying hydrogeological processes in other limestone systems in climatically similar areas.
Climate change, drought, springs, limestone aquifers, Central Italy
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