Modelling the historical and future evolution of six ice masses in the Tien Shan, Central Asia, using a 3D ice-flow model

Abstract

In the Tien Shan, few modelling studies exist that examine in detail how individual ice bodies are responding to climate change. Nonetheless, earlier research demonstrated that the glacier response to climate change in this mountain range is heterogeneous. Here, we use several measurements and reconstructions of the ice thickness, surface elevation, surface mass balance, and ice temperature to model in depth six different ice bodies in the Kyrgyz Tien Shan: five valley glaciers and one ice cap. The selected ice masses are located in different sub-regions of the Tien Shan with different climatic and topographic settings, and they are all characterized by detailed recent glaciological measurements. A three-dimensional higher-order thermomechanical ice-flow model is calibrated and applied to simulate the evolution of the ice masses since the end of the Little Ice Age (1850) and to make a prognosis of the future evolution up to 2100 under different Coupled Model Intercomparison Project Phase 6 (CMIP6) shared socioeconomic pathway (SSP) climate scenarios. The results reveal a strong retreat of most of the ice masses under all climate scenarios, albeit with notable variations in both timing and magnitude. These can be related to the specific climate regime of each of the ice bodies and their geometry. Under a moderate warming scenario, the ice masses characterized by a limited elevation range undergo complete disappearance, whereas the glaciers with a larger elevation range manage to preserve some ice at the highest altitudes. Additionally, our findings indicate that glaciers that primarily receive precipitation during the late spring and summer months exhibit a more rapid retreat in response to climate change, while the glaciers experiencing higher precipitation levels or more winter precipitation remain for a longer duration. Projections concerning the overall glacier runoff reveal that the maximum water discharge from the ice masses is expected to occur around or prior to the middle of the 21st century and that the magnitude of this peak is contingent upon the climate scenario, with a higher warming scenario resulting in a higher peak.