Unprecedented snow-drought conditions in the Italian Alps during the early 2020s

Abstract

Snow represents a fundamental water resource for mountain and lowland areas. Changes in the frequency and magnitude of snow droughts can significantly impact societies and ecosystems that rely on snowmelt to satisfy their water demands. Here we documented and quantified the snow drought that affected the Italian Alps during the early 2020s. We used 15 long-term snow-depth series (period 1930–2023, elevation range: 864–2200 m a.s.l.) to simulate the snow water equivalent (SWE), in conjunction with climatic reanalysis data and river discharge observations. We found that the March SWE anomaly in 2022 reached the lowest value in the last century, due to an unprecedented combination of drier- and warmer-than-normal conditions in the period December 2021–March 2022. This event contributed to causing critical hydrological conditions in the Po and Adige rivers which, during Summer 2022, experienced the worst hydrological drought ever recorded. Despite its unprecedented magnitude, the snow drought in 2022 is part of a recent pattern of increased intensity and frequency of snow-drought events since the 1990s, due to the combined increasing occurrence of warmer- and drier-than-normal climatic conditions during the snow season. Strikingly, during Winter 2022/2023, the March SWE anomaly reached the third lowest value in the analysed period, resulting in exceptional snow droughts during two consecutive winters. The snow-drought conditions that occurred in the early 2020s in the Italian Alps warn of the pressing need for the implementation of impact mitigation measures to adapt to the fast changing snow and climatic conditions.

Drought in the Po Valley: Identification, Impacts and Strategies to Manage the Events

“…Nonetheless, the 2022-2023 event was identified independently from the index used. The bulletins of the ADBPO reported reduced streamflow, low precipitation (in terms of both rainfall and snow) and high temperatures and are coherent with the cited literature, that underlines the exceptionally low river discharge [13], the extremely negative SWE [18] and the negative values of AI [26]. The 2003 event was again detected by the major part of the considered indices: SPI, SPEI, NDVI and river discharge.…”

“…The 2022-2023 drought is regarded as the most severe event that has affected the Po Valley. Actually, the mean Po River flow observed in summer 2022 was the lowest in the past two centuries [13]; the March 2022 Snow Water Equivalent (SWE) broke all negative records over the 1930-2023 period [18], and there has been a sequence of severely dry seasons (December-August and February-August) with no precedents with respect to the 1976-2005 period [14].…”

“…Agricultural drought indices such as the Normalized Difference Vegetation Index (NDVI) are used by [27], while indicators employed for the detection of hydrological drought, as the river discharge and the water level are used in many works (as for example [22,23]), together with the Standardized Annual Streamflow (SAS) reconstructed by [5]. The Snow Water Equivalent is applied by [18] to evaluate the anomaly in snow and thus detect the contribution given by the lack of snow to the drought conditions.…”