Detection and attribution of hydrological changes in a large Alpine river basin

The Alpine region is a particularly sensitive environment rich in water resources nurturing delicate freshwater ecosystems, which are however threatened by intensive exploitation for hydropower production and irrigated agriculture. The impact of water uses on the hydrological cycle is intimately intertwined with changes of the climatic forcing, which operate over a wide range of temporal and spatial scales. In the present study historical time series of streamflow, precipitation and temperature, recorded in the Adige River Basin, a large Alpine watershed in northeastern Italy, are analyzed in order to quantify alterations of the main hydrological fluxes due to changes in climate and water uses. Spatial and temporal patterns of change are detected by comparing annual and seasonal components of the water budget performed in four representative sub-catchments (with size ranging from 207 to 9852km2) characterized by different climatic and water use conditions. Afterwards, a multi-method approach is applied for attributing the observed changes to their main drivers. Summer streamflow depletion affects the Adige lowlands since the ’70s, which is attributed to both the reduction of winter precipitation and the development of irrigated agriculture. Conversely, winter streamflow increased in headwater catchments due to the increase of aquifers recharge in autumn, which is consistent with the increase of precipitation in the same period. These results reveal that the impact of climate change on the Adige Basin is multifaceted, scale-dependent and intertwined with the effects of changes in water resources exploitation.