The Glaciers of the Dolomites: last 40 years of melting

Abstract. Small Alpine glaciers located below the regional equilibrium line altitude are experiencing considerable ice losses and are expected to fragment into smaller glacial bodies and eventually disappear. Monitoring such glaciers through remote sensing is often challenging because of the incompatibility between their size and the spatial resolution of satellites. The Italian Dolomites (S-E Alps) are a region clearly illustrating such challenges and where no long-term glacier mass balance data are available. This renowned Alpine sector hosted tens of glaciers up until a few decades ago, with now only twelve remaining. This study presents a multi-decadal (1980s–2023) estimation of surface elevation change and geodetic mass balance of the current mountain glaciers present in the area. Calculations are based on geodetic data: high resolution and accuracy is obtained with unmanned aerial vehicle (UAV) Structure from Motion (SfM) and airborne Light Detection and Ranging (LiDAR), from 2010 to 2023. SfM on historical aerial imagery is used for previous decades. We found an average cumulative surface elevation change of -28.7 m from 1980s to 2023, 33 % of which between 2010–2023. The average mass balance rate for the whole period is -0.64 ± 0.05 m w.e. yr^-1, varies significantly between sites, and is negative with a smaller amplitude than the Alpine reference glaciers mass balance. Regionally, 66 % of the entire volume loss is related to the Marmolada Glacier alone. Mass losses are accompanied by areal reductions evidencing that the Dolomites are rapidly losing their glaciers. This study aims to address the existing lack of multi-decadal data for the Dolomites by providing a quantitative account of the current state of these small glacial bodies.