Changes of the Hydrologic regime over the last 90 years in the Flumendosa basin, Sardinia.

English Abstract:

In Mediterranean climates during the winter months much of the precipitation recharges sub-surface and surface reservoirs. However, in the late winter and early spring, when vegetation growth conditions are favorable, much of the precipitation can be depleted by transpiration and, furthermore, runoff reduced directly by the increased vegetation cover. In the Mediterranean regions there is the evident effect of climate changes that it is causing several problems on the water resources availability. Several scientists have shown a strong decreasing trend in winter precipitation amounts and an evident shifts in how the precipitation is distributed across the winter and spring months. Considering that the most of the runoff to surface reservoirs occurs in the winter months and that spring hydrologic response is likely to be influenced strongly by vegetation, these precipitation changes can be considered hydrologically important. Case study is the Flumendosa basin (Sardinia), which is characterized by a reservoir system that supplies water to the main city of Sardinia, Cagliari. Data are from 42 rain gauges stations (1922-2007 period) over the entire basin and data of runoff are available for the same period. In the Flumendosa reservoir system the average annual input from stream discharge in the latter part of the 20th century was less than half the historic average rate, while the precipitation over the Flumendosa basin has decreased, but not at such a drastic rate as the discharge, suggesting a marked non-linear response of discharge to precipitation changes. Trends in precipitation series and in the number of wet days were examined using the Mann-Kendall trend test and the relationship between winter precipitation and large scale pressure indices, such as the North Atlantic Oscillation has been investigated in this study, showing high correlation and a strong decrease of precipitation during the winter season.

In Mediterranean climates during the winter months much of the precipitation recharges sub-surface and surface reservoirs. However, in the late winter and early spring, when vegetation growth conditions are favorable, much of the precipitation can be depleted by transpiration and, furthermore, runoff reduced directly by the increased vegetation cover. In the Mediterranean regions there is the evident effect of climate changes that it is causing several problems on the water resources availability. Several scientists have shown a strong decreasing trend in winter precipitation amounts and an evident shifts in how the precipitation is distributed across the winter and spring months. Considering that the most of the runoff to surface reservoirs occurs in the winter months and that spring hydrologic response is likely to be influenced strongly by vegetation, these precipitation changes can be considered hydrologically important. Case study is the Flumendosa basin (Sardinia), which is characterized by a reservoir system that supplies water to the main city of Sardinia, Cagliari. Data are from 42 rain gauges stations (1922-2007 period) over the entire basin and data of runoff are available for the same period. In the Flumendosa reservoir system the average annual input from stream discharge in the latter part of the 20th century was less than half the historic average rate, while the precipitation over the Flumendosa basin has decreased, but not at such a drastic rate as the discharge, suggesting a marked non-linear response of discharge to precipitation changes. Trends in precipitation series and in the number of wet days were examined using the Mann-Kendall trend test and the relationship between winter precipitation and large scale pressure indices, such as the North Atlantic Oscillation has been investigated in this study, showing high correlation and a strong decrease of precipitation during the winter season.