Determination of Annual Ablation of the Doloonnuur Glacier on Munkhkhairkhan Mountain, Mongolian Altai, Using a Degree-Day Model

Mongolia is among the ten countries most vulnerable to global warming and climate change. Mid-term observations from western Mongolia indicate that the mean annual air temperature increased by 2.08 °C between 1940 and 2017, exerting a strong influence on glacier melt and area shrinkage in high mountain regions. This study estimates the annual melt of the Doloon Nuur Glacier, located on Munkhkhairkhan Mountain in the Mongolian Altai, using a degree-day model (DDM) and evaluates the results against in situ stake measurements. Air temperature data recorded by an automatic weather station between 15 June 2023 and 15 June 2024, together with ablation stake measurements installed on 15 June 2023, were used in the analysis. The cumulative positive degree days (PDD) amounted to 844.8 °C·day over the study period. Applying a degree-day factor of 6.0 mm w.e. °C⁻¹ day⁻¹, the calculated annual melt reached 5.06 m in the lower glacier zone, 4.2 m in the middle zone, and 3.1 m in the upper zone, yielding a glacier-wide mean melt of 4.1 m. The modeled melt shows good agreement with the observed mean stake ablation of 3.6 m, with a difference of 0.5 m, supporting the reliability of the degree-day approach in this region. Between 2023 and 2024, the glacier ablation area decreased by 5.3 ha (≈5%), corresponding to an estimated ice volume loss of 2.18 × 10⁵ m³, indicating a clear and measurable impact of climate change on glaciers in the Mongolian Altai. These results demonstrate that temperature-based modeling provides a robust framework for assessing glacier mass loss in Mongolia and offers a valuable data foundation for long-term glacier mass-balance monitoring and climate-change impact assessments in data-scarce mountain regions.