From snow to socio-hydrology: mechanisms behind the 2022 drought in the Alps

Our study delves into the intricate relationship between the 2021-2022 snow deficit in the Italian Alps and subsequent socio-hydrologic repercussions during the ensuing summer drought across the Po river basin, thus elucidating socio-hydrologic response from headwaters to lowlands in an era of change. Starting from early 2022, a high-pressure ridge led to a -88% anomaly in peak Snow Water Equivalent (SWE), which was compounded by episodes of intraseasonal snowmelt and earlier melt-out dates. As a result of this low SWE, a further -10% in summer precipitation, and +1.9°C summer temperature anomaly, terrestrial water storage measured through GRACE hit its all-time low. Meanwhile, we observed an intensification of both anomalies in SWE and in streamflow compared to other recent droughts. Municipal emergency water-use restrictions were issued in correspondence to the peak in snowmelt deficit, rather than the peak in precipitation deficit, with a spatial signature that clearly points to missed snowmelt as a key contributing factor in the escalation of this emergency. This archetypal event, along with the multi-decadal decline in terrestrial water storage, highlights the contributing role of snowmelt deficit in driving socio-hydrologic impacts of droughts in Alpine regions in the context of a warming climate.