Energy and mass balance modelling for glaciers on the Tibetan Plateau : extension, validation and application of a coupled snow and energy balance model

The Tibetan Plateau is the source region of five of the largest Asian rivers. The large amount of ice, snow and permafrost on the plateau and its surrounding mountain ranges and the stored water therein is important in sustaining seasonal water availability. According to the overall trend of increasing air temperatures on the Tibetan Plateau and its adjacent areas since several decades, most glaciers are retreating. The regional patterns of glacier change are contrasting, influenced by local factors and the spatial and temporal heterogeneity of climate and climate variability. The individual feedback mechanisms between atmosphere and glacier, and the role of the various components of the glacier surface energy and mass balance in the melt process for different climate regions on the Tibetan Plateau have not yet been analysed in detail. This thesis deals with the modelling of glacier surface energy and mass balances on the Tibetan Plateau. Four glaciers and one ice cap on the plateau and its surrounding mountain ranges form the regional study sites: Zhadang glacier (south eastern Tibetan Plateau), Purogangri ice cap (central plateau), Naimona’nyi glacier (western Himalayas), Halji glacier (western Himalayas) and Muztag Ata glacier (eastern Pamirs). The study sites have a maximum distance of ≈1700 km from each other and are located in different climate regions. As it is the case for most remote regions of the world, data availability from in-situ observations is insufficient for more complex, physically-based glacier energy and mass balance models. Hence, we use the in-situ measurement data from the intensive observation period at Zhadang glacier to evaluate the surface energy and mass balance model performance in detail. For decadal model simulations high resolution atmospheric model data from the High Asia Reanalysis is applied. The model scheme couples the atmospheric energy balance to a subsurface multi-layer snow module in order to analyse the atmosphere-cryosphere interactions. For Zhadang glacier the different model components are thoroughly validated using different methods and data sources. The installed complex monitoring system including a time-lapse camera system at Zhadang glacier is the first of its kind on the Tibetan Plateau. It provides an excellent data base for model evaluation and provides new opportunities for further analysis. The developed surface energy and mass balance model is applied to the five study sites. From every regional study we obtain a 10year time series of glacier-wide surface energy and mass balance components. At each study site model results are compared to either in-situ meteorological or glaciological data or remote sensing analyses which provide evidence for further constraints regarding the tuning parameters of the modelling chain. This is the largest and most detailed homogeneous glaciological data set from the Tibetan Plateau so far regarding the modelling of surface energy and mass balance. The thesis contributes to a further and detailed understanding of the role of the various energy and mass balance components for glacier change in the different climate regions of the Tibetan Plateau. It serves to increase knowledge on the various driving mechanisms for the energy and mass balance components. The findings are crucial for estimating future glacier evolution. It forms the basis for further analysis and research on glacier related water availability on the Tibetan Plateau.