Evolution of freshwater availability in a climate‐changing Mediterranean context: The case of Umbria region, central Italy

Freshwater availability is the litmus test of the ongoing global warming, but local effects in relation to larger scale behaviours are often ambiguous. In this study, 19 indicators derived by historical rainfall and temperature records have been used to reconstruct climatic trends over the Umbria region (central Italy). The scenario emerging from observations of the last 70–100 years consists in increasing air temperatures and decreasing yearly precipitation depths, which are differently distributed over the 12 months with respect to the past. As a second step, the response in terms of freshwater availability has been assessed by analysing runoff and groundwater records. A clear reduction in yearly water volumes flowing through the outlet stations of five pilot basins during the last century (1927–2020) has been found, quantified in a median loss rate of equivalent surface water thickness of −1.62 mm/year. Monthly mean groundwater levels show a slight increasing trend for most of the monitoring stations, but such an analysis has been carried out over a limited and more recent period (2006–2020). Hence, it can be affected by the uncertainty commonly associated to the interpretation of trend analyses referring to short temporal windows. This last critical point is strengthened by an analysis of the runoff volume limited to the period 2006–2020 from which, in contrast with the results provided by the aforementioned long-term investigation, an increasing trend has been derived.