The 2022 - 2023 snow drought in the Italian Alps doubled glacier contribution to summer streamflow

Glaciers are vital resources for regulating water availability in mountainous regions, but their reducing size due to climate change threatens this crucial role, particularly during increasingly frequent and severe snow droughts. The exceptional 2022 and 2023 snow-drought episodes in the Italian Alps provide a critical opportunity for examining the role of glacier melt in mitigating drought impacts and analyse glacier response to these extreme events. This study thus investigates the impact of the 2022-2023 snow droughts on glacier melt contribution to summer streamflow in the Italian Alps, focusing on the Aosta Valley and Lombardy regions. We utilize glacier mass balance data collected from ablation stakes scattered over different glaciers and streamflow data from the Dora Baltea and Adda rivers to validate glacier melt estimates by S3M Italy, a spatially distributed operational cryospheric model. Once validated, we use glacier melt simulations generated using the S3M Italy to analyse how glacier melt contribution to streamflow during the snow droughts of 2022 and 2023 compared to the median of 2011-2023. Our findings reveal a substantial increase in glacier melt contribution to streamflow during 2022 and 2023 snow droughts. In both regions, the contribution of glacial melt to streamflow nearly doubled or tripled compared to average values from 2011-2023. Both 2022 and 2023 droughts resulted in an earlier onset of the melt season; however, 2022 was characterized by an earlier melt peak, while 2023 showed a prolonged melt season. These results emphasize the significant contribution of glacier melt to streamflow during severe drought events, highlighting the importance of considering glacial dynamics in developing robust water management strategies for alpine environments. The increasing frequency and severity of droughts underscore the urgency of this need.