Cryosphere changes and their impacts on regional water resources in the Chinese Altai Mountains from 2000 to 2021

The cryosphere has an important impact on regional water resources and ecosystems in the Chinese Altai Mountains and its piedmont zone. Using the latest remote-sensing datasets of cryosphere changes and combining with in-situ observation data from glacier monitoring stations and snow cover surveys, the main cryosphere elements including glaciers, snow cover, and permafrost are investigated with emphasis on their changes since 2000 and the current situation. Their water resource effects are also discussed. The results indicate that although the glaciers in the region have experienced continuous and intensive melting, mass loss has slowed because both glacier area shrinkage and thickness reduction were larger during 2000-2010 than during 2010-2021. Snow cover water equivalent (w.e.) has increased due to obvious increases in snow depth, although snow-cover area has decreased slightly. Permafrost has been degrading. Overall, cryosphere contributions to the regional water resource are approximately 40.9% since 2000, among which snow-cover melting is the largest, contributing 37.1% to water resources in the Irtysh River Basin and significantly more in the mountainous sub-basins with increased snowfall. Glacier melting contributes 2.9%-3.4%, lower than earlier estimations of 3.4%-3.6% for the late 20th century. Permafrost thaw caused by active layer thickening contributes approximately 0.59%. Meteorological data shows a warming and wetting trend, but summer temperature has a much lower increase rate and a slowing increase trend after 2013. Moreover, snowfall frequency has increased. In the future, glacier water resource contribution will continue to decrease, but the water resource effects of snow-cover melting and permafrost degradation would increase.