Evaluating Glacier Melt's Role in Mitigating Hydrological Droughts in Mountainous Regions: Insights from the Adige River Basin

Glacier meltwater is critical in sustaining streamflow during low-flow periods in mountainous regions. Nevertheless, glacier melt is often poorly or statically assessed in hydrological simulations, leading to partial considerations for effectively managing water, especially during droughts.

This study evaluates the contribution of glacier melt to summer flows and its capacity to mitigate hydrological droughts in the upper Adige River basin, located in the Italian Alps (6900 km²). To achieve this, a new dynamic glacier module was implemented into the ICHYMOD-TOPMELT hydrological model, enabling annual updates of glacier area and improved quantification of meltwater contributions under progressive glacier retreat (from 122 km² in 1997 to 84 km² in 2017).

The hydrological model exhibited robust performance metrics, with Kling-Gupta Efficiency (KGE) values of 0.82 for the overall study period and 0.65 for summer low-flow months. The dynamic glacier module accurately captured observed glacier area, mass balance, and seasonal melt trends. Validation against ASTER-derived glacier mass balance data for 2000–2019 revealed an error of 11%, underscoring the model’s ability to effectively represent long-term glacier dynamics.

Results indicate that glacier melt contributed an average of 5.86% to summer streamflow during the period 1997–2019, with significant spatial variability. In drier, more glacierized subbasins, melt contributions reached up to 30–40%, highlighting its importance in maintaining streamflow where precipitation is scarce. We analyzed also the interplay between snow water equivalent (SWE), temperature, and glacier melt during droughts, with SWE acting as a buffer to delay summer glacier melt under cooler conditions.

Severe drought years (like 2003, 2005, and 2022) demonstrated considerable variability in glacier melt contributions. In 2003, high temperatures and limited SWE led to glacier melt accounting for 14.4% of summer flows. By contrast, colder temperatures in 2005 reduced contributions to 6.3%. In 2022, while high temperatures drove glacier melt, reduced glacier areas led to lower absolute contributions (8.2%) compared to earlier droughts. If we had the same glacier area in 2022 like in 1997, glacier contribution could have been up to 14.6 %.

Findings highlight the declining capacity of glacier melt to buffer against hydrological droughts due to ongoing glacier retreat. With shrinking glaciers, future summer flows in the Adige River basin are expected to become increasingly dependent on precipitation and snowmelt, thereby heightening the vulnerability of water resources to climate variability.

Additionally, simulations showed that models using a static glacier area tend to overestimate glacier melt contributions, emphasizing the necessity of integrating a dynamic glacier modeling framework in hydrological models. These frameworks are crucial for accurately projecting future water availability and informing adaptive water resource management strategies in glacier-fed catchments.