| 12 Jan 2026
Retreating glaciers and snow cover are amplifying summer droughts in the Adige River Basin (Italy)
Abstract. Snow and glacier meltwater play a critical role in sustaining summer streamflow in mountains and downstream regions. Yet, understanding glaciers' contributions to buffer river streamflow during droughts remains limited and pose major barriers to improve present and future water management within the context of climate change.
This study evaluates the contribution of glacier melt to summer flows and its mitigation effect of hydrological droughts in the upper Adige River basin, (Italy). We developed and implemented a new dynamic glacier module into the ICHYMOD-TOPMELT hydrological model, annually updating glacier area and improving the quantification of meltwater contributions under progressive glacier retreat (from 111 km2 in 1997 to 79 km2 in 2017).
The hydrological model exhibited robust performances (KGE = 0.89 for 1997–2022; 0.88 in summers) capturing observed glacier area, mass balance, and seasonal melt trends. Results show that glacier melt in the upper Adige River basin contributed to an average of 4.5 % to total summer streamflow during 1997–2022, with significant spatial variability and reaching 30 % in glacierized subbasins. During the severe drought of 2003, 2005 and 2022, glacier melt contributions ranged between 4 and 12 % at the upper Adige closing section. In 2003, high temperatures and limited SWE led to glacier melt accounting for 11.67 % of summer flows. By contrast, colder temperatures in 2005 reduced contributions to 4.85 % compounding with low SWE conditions and leading to a significative runoff deficit. In 2022, the combination of low precipitation, low snow cover and high temperature drove glacier melt. Differently than the 2003 drought, reduced glacier areas led to lower absolute contributions (8.17 %).
Our findings reveal that despite the increased melt rates in recent warm years, retreating glacier areas have reduced their absolute buffering effect. Glacier retreat is weakening their contribution to summer flows, increasing the upper Adige River basin's dependence on precipitation and snowmelt, which is also showing a decreasing trend. For these reasons, accounting for dynamic glacier and snow changes is essential to improve future drought projections and inform adaptive water management in glacier-fed basins within the context of climate and anthropogenic changes.
