Influence of climatic variations on the groundwater of mountains areas: the cases of Mount Cucco and Gualdo Tadino Mountains (Central Apennines)

This paper presents the results of a hydrogeological research carried out over two anticlines "Monte Cucco" and the contiguous "Monti di Gualdo" (belonging to the Umbria-Marche Sequence) in Central Italy. The structures, made up of carbonate rocks, are quite similar from both a morphological and lithological point of view. The main difference is the presence of deep karst in the Calcare Massiccio formation of Monte Cucco. The available hydrogeological and climatic data are scarce and not always as reliable as they should be; however the climatic data indicate, over the two structures, similar rainfall and evapotranspiration. Both anticlines are surrounded by springs, mainly located at the contact between the Maiolica limestone formation and the Marne a Fucoidi marly formation. The springs located around Monte Cucco have a total average discharge (per unit area of potential recharge) lower than the Monti di Gualdo's springs. The estimated average yearly water budget indicates that on Monte Cucco the infiltration is about 30% higher than the total discharge from the springs; this can be explained assuming that part of the infiltration feeds a deep flow, parallel to the anticline axial plane. There are no indications of a similar situation for the Monti di Gualdo, over which the average infiltration corresponds, in practice, to the total average discharge of the springs. Actually there is a possibility that the different behavior of the structures is only apparent, and that the reported difference is due to the inaccuracy of the data: however such a possibility appears to be rather remote, as the difference is quite large. In Central Italy, temperature increased and rainfall decreased during the 20th century; according to recent researches, a rainfall decrease up to 30% is likely to occur in the next decades. This scenario points towards a large decrease of recharge and thus of the discharge of the springs. Such a situation is more alarming for a structure like the Monte Cucco, than for structures like the Monti di Gualdo, as in the case of Monte Cucco the recharge areas of the springs and of the regional flow are bounded by dynamic groundwater divides, which move horizontally as the water table lowers or rises. As the water table lowers, the groundwater divides move towards the springs located higher up, producing a drastic reduction in the discharge of the springs, higher than the reduction of the groundwater recharge. The results of the research confirm the need to reorganize the water management of the area; such management must be based on a good network of hydro-meteorological data, coupled with field and modelling investigations.