Historical Climate Change of the Sardinian hydrology: The dramatic runoff decrease in the last three decades.

Abstract:

From 80’ surface runoff decreased systematically in main Sardinian basins with dramatic consequences on water resources system. Indeed, Sardinian water resources system is regulated by more than 50 main dams, which accumulate runoff during the rainy seasons (Autumn and Winter). The effect is that in last years the water levels in the reservoirs decreased significantly and systematically.

In this sense an analysis of the precipitation, temperature and runoff regimes for the whole Sardinia has been performed. We collect an innovative database of rainfall, temperature and runoff observations from 1918 to 2011, including data of more than 400 rain stations, 30 discharge stations and 180 thermometric stations. Hystorical trends are detected using the Mann Kendall, with a significance level of 5%, showing a decrease of the rainfall in the winter period and, more marked, of the runoff, for the whole Sardinia generally, with dramatic consequences for agriculture and water availability. Interestingly, the decrease is more marked for the rain and discharge stations of the Sardinian west coast, exposed to the west european climate dynamics.

In this sense, several studies have shown a significant correlation between the main meteorological variables and indices related to fluctuations in global scale, for example NAO (North Atlantic Oscillation). A negative NAO brings to an increased storm activity and rainfall to southern Europe and North Africa.

We found high negative correlations between NAO and precipitation and runoff during the winter season, and the correlations decrease with the increase of rain station longitudes. The results show a strong negative correlation at the stations and basins of the Sardinian west coast, which is due to the exposure to the mistral winds and the storm track dynamics. Instead a less negative correlation has been estimated for the east coast stations, due to the impact of the horography that attenuate the large scale atmospheric dynamics.