Linking observed glacier mass losses and streamflow trends globally

Ongoing glacier retreat is causing the loss of a critical water resource in mountain regions, with wide-ranging downstream impacts. These include shifts in streamflow seasonality, change in water availability, and changes to low-flow conditions, either exacerbating or alleviating them. To date, most hydrological impact studies have relied on model simulations for specific regions or catchments, often driven by future climate change scenarios. However, evidence on the hydrological impact of glacier retreat based on direct observational data is scarce due to the limited accessibility of in-situ data. To address this, we have assembled a comprehensive dataset of streamflow observations from approximately 600 glacierized catchments (10–1000 km²) around the world. By integrating this dataset with geodetic estimates of glacier mass change for each individual glacier globally, we quantify the contribution of net glacier mass loss to streamflow across diverse mountain regions. Our study identifies where decadal glacier mass losses (2000–2010 and 2010–2019) align with observed streamflow trends in both magnitude and direction, and where other hydrological processes are more dominant. Streamflow trends and variations are analyzed both at an annual and seasonal scale with a specific focus on hydrograph characteristics such as high flows, low flows, and the melt season. Our results highlight the spatial heterogeneity of glacier retreat impacts across mountain regions and their downstream implications.