Chang et al. (2026) Future projections of cryosphere degradation and its hydrological impacts in the upper Bulgan River basin, Altai Mountains

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-09-25
• Authors: Zehua Chang, Leilei Yong, Yahui Wang, Kang Wang, Batsuren Dorjsuren, Otgonbayar Demberel, Hongkai Gao
• DOI: 10.1016/j.ejrh.2026.104009

Research Groups

• Key Laboratory of Geographic Information Science (Ministry of Education of China), School of Geographical Sciences, East China Normal University, Shanghai, China
• Training Laboratory for Environmental Studies, Department of Environment and Forest Engineering, School of Engineering and Technology, National University of Mongolia, Ulaanbaatar, Mongolia
• Altai Mountain Cryosphere & Disaster Research Laboratory, School of Applied Sciences, National University of Mongolia, Ulaanbaatar, Mongolia
• Department of Geography, Physics, and Engineering of Western Regional Branch, Western Regional branch of the National University of Mongolia, Khovd, Mongolia

Short Summary

This study uses the FLEX-Cryo model driven by 13 bias-corrected CMIP6 models to project future cryosphere degradation and hydrological changes in the upper Bulgan River basin, Altai Mountains. It finds no significant trend in annual runoff but significant seasonal shifts, including increased winter runoff, decreased summer runoff, and advanced runoff timing, alongside widespread glacier and permafrost degradation.

Objective

• To project future cryosphere degradation (glaciers, snow, permafrost) and its hydrological impacts (runoff changes, timing) in the nested Baitag and Duchinjil catchments of the upper Bulgan River basin, Altai Mountains, under SSP2–4.5 and SSP5–8.5 climate change scenarios.

Study Configuration

• Spatial Scale: Nested Baitag (7392.86 km²) and Duchinjil (2931.09 km²) catchments in the upper Bulgan River basin, Altai Mountains, western Mongolia. Elevation ranges from 1190 to 4190 m a.s.l. (Baitag) and 1900 to 3850 m a.s.l. (Duchinjil).
• Temporal Scale: Historical period for model calibration and evaluation (1993–2023 for Baitag runoff and meteorological data, 1993–2021 for Duchinjil runoff). Future projections cover 2024–2100.

Methodology and Data

• Models used:
  • FLEX-Cryo: A semi-distributed hydrological model (based on FLEX-Topo framework) simulating snow accumulation/melt, glacier melt/geometric evolution, and effects of soil freezing/thawing on runoff.
  • Δh parameterization: Used for glacier geometry evolution.
  • Stefan equation: Used for estimating soil freeze and thaw depths.
  • Hamon equation: Used for estimating potential evaporation.
• Data sources:
  • Observations: Daily runoff (Baitag: 1993–2023; Duchinjil: 1993–2021), daily air temperature and precipitation (Duchinjil meteorological station: 1993–2023).
  • Cryospheric Data: Global glacier thickness dataset (Farinotti et al., 2019), WGMS-AMCE dataset for glacier mass balance (Dussaillant et al., 2025; WGMS, 2026), MODIS snow cover data (Hall et al., 2006), high-resolution permafrost distribution and active layer thickness (ALT) dataset from NIEER (Ran et al., 2021, 2022).
  • Climate Projections: Daily air temperature and precipitation from 13 CMIP6 global climate models (GCMs) under SSP2–4.5 and SSP5–8.5 scenarios, bias-corrected using local observations.

Main Results

• Glacier Degradation: Glaciers in Duchinjil are projected to disappear completely around 2060 (by 2057 under SSP2–4.5 and 2061 under SSP5–8.5). In Baitag, small glacier remnants persist by 2100, with volume decreasing to 0.05 km³ (SSP2–4.5) and 0.002 km³ (SSP5–8.5).
• Snow Cover Changes: Annual maximum snow depth at Duchinjil station increases by 0.23 cm/decade (SSP2–4.5) and 0.47 cm/decade (SSP5–8.5). Annual snow cover duration decreases by 0.71 days/decade (SSP2–4.5) and 3.09 days/decade (SSP5–8.5).
• Permafrost Degradation: Permafrost area in Baitag decreases from ~76% initially to ~48% (SSP2–4.5) and ~8% (SSP5–8.5) by 2099. The lower limit of permafrost moves upward to 2450–2650 m (SSP2–4.5) and 2700–3250 m (SSP5–8.5) by 2099. Mean active layer thickness (ALT) increases from ~2.25 m to ~2.95 m (SSP2–4.5) and ~3.42 m (SSP5–8.5) by 2099.
• Annual Runoff: Ensemble mean annual total runoff shows no significant linear trend in either catchment during 2024–2100. Catchment-averaged annual glacier runoff depth decreases to less than 0.5 mm in Baitag and to 0 mm in Duchinjil.
• Seasonal Runoff Shifts: Winter runoff increases (0.08–0.43 mm/decade), while summer runoff decreases (0.39–1.57 mm/decade) in both catchments. Summer runoff decreases approximately twice as fast in upstream Duchinjil as in Baitag.
• Runoff Timing Advance: Under SSP5–8.5, peak runoff advances by approximately 18 days in Baitag and 38 days in Duchinjil between 2030–2034 and 2090–2094. The onset of spring runoff rise advances by about 17 days in Baitag and 18 days in Duchinjil.

Contributions

• First application of the FLEX-Cryo model to assess future cryosphere and hydrological changes in the upper Bulgan River basin, Altai Mountains, a cold and arid mountain region with limited glacier cover and widespread permafrost.
• Provides comprehensive projections of glacier, snow, and permafrost degradation, highlighting their distinct impacts on runoff components and timing.
• Demonstrates that future hydrological changes in such regions are primarily manifested in seasonal runoff shifts (increased winter, decreased summer) and advanced runoff timing, rather than significant changes in annual total runoff volume.
• Compares cryospheric and hydrological responses between nested catchments, revealing greater seasonal changes and timing advances in the upstream Duchinjil catchment.
• Emphasizes the critical need for water resource assessments in similar cold and arid mountain catchments to focus on seasonal runoff changes, peak timing, summer runoff reduction, and winter baseflow.

Funding

• National Key Research and Development Program of China (2024YFE0113200)
• National Natural Science Foundation of China (42471040)
• National University of Mongolia (grant agreement P2025-5037)
• Mongolian Science and Technology Foundation (grant CHN-2024/12)

Citation

@article{Chang2026Future,
  author = {Chang, Zehua and Yong, Leilei and Wang, Yahui and Wang, Kang and Dorjsuren, Batsuren and Demberel, Otgonbayar and Gao, Hongkai},
  title = {Future projections of cryosphere degradation and its hydrological impacts in the upper Bulgan River basin, Altai Mountains},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.104009},
  url = {https://doi.org/10.1016/j.ejrh.2026.104009}
}