From Snow to Rain: Elevation-Dependent Drought Responses and Drivers in a Large Italian Alpine Catchment.

Drought has recently emerged as a common hazard in Alpine regions, where snow
dynamics strongly influence river flow regimes and play a crucial role in reservoir filling,
irrigation, tourism, and ecosystem sustainability. Reduced snow contributions and
warmer winters, which enhance rainfall at the expense of snowfall, can shift the
hydrological behaviour of Alpine catchments toward regimes typical of lower elevations.
In this study, we assess the main drivers of drought in the Adige River basin, a large
Italian Alpine basin characterized by sub-catchments spanning a wide range of
elevations over the period (1980-2018). We further investigate the seasonality and
characteristics of drought events across elevation bands to identify the drought types
with the greatest impacts in terms of total severity and duration. Our results show that
cold-season snow drought is the dominant drought type over the study period, followed
by snowmelt drought and rainfall deficit drought. Mid- and high-elevation sub-
catchments are particularly affected by cold season and snowmelt drought, whereas
low-elevation areas are mainly impacted by rainfall deficit drought. These findings
highlight the need for adaptation strategies that explicitly account for seasonal drought
processes and elevation-dependent river responses to sustain mountain water systems
under increasing drought conditions, especially given the implications for hydropower
production, irrigation, and tourism.