Accelerated Glacier Retreat, Mass Balance Deficits, and Downstream Hydrological Consequences Across Six Mountain Regions (2000-2024)

Mountain glaciers are among the most sensitive indicators of atmospheric warming, responding to temperature and precipitation changes on decadal timescales through area loss, thickness reduction, and mass balance deficits that collectively constitute the cryosphere's contribution to observed sea level rise. The acceleration of glacier retreat documented since the 1990s has intensified markedly in the 2010s and early 2020s, with global glacier mass loss in 2021–2023 representing the highest three-year loss on record. This study presents a twenty-four-year remote sensing and field-based analysis of glacier area change, mass balance, and downstream river discharge trends across 124 glaciers spanning six mountain regions — the European Alps, Icelandic Ice Caps, New Zealand Southern Alps, Canadian Rockies, Central Asian Pamirs, and Scandinavian Mountains.Landsat and Sentinel-2 multispectral imagery was used to map glacier outlines at five-year intervals from 2000 to 2024. Geodetic mass balance was estimated from DEM differencing using SRTM and TanDEM-X elevation models. Downstream river discharge records from 214 hydrological stations were analysed for trend and peak-flow timing shifts. Results demonstrate mean area loss of 18.6 percent across all study glaciers, with the European Alps showing the greatest proportional loss (26.4%). Peak streamflow timing advanced by a mean of 22.4 days across downstream basins, signalling transition from glacier-buffered to snowmelt-dominated hydrological regimes.