Remote sensing derived spatial patterns of glacier mass balance in Tibet
- Durch Fernerkundung ermittelte räumliche Muster der Gletschermassenbilanz in Tibet
Spiess, Marinka; Lehmkuhl, Frank (Thesis advisor); Schneider, Christoph (Thesis advisor); Scherer, Dieter (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2016
The climate has changed on the Tibetan Plateau. The air temperature has shown distinct increase since the 1960s, exceeding the increase in other land areas of the same latitudinal position in the Northern Hemisphere. The retreat of Tibetan glaciers in connection with climate change is of interest since the glacierized areas constitute important freshwater resources - which, among others, provide the basis for all livelihoods on the plateau. Furthermore, the glaciation and snow cover of Tibet are crucial to feedback mechanism in the global climate system. Glacier retreat has been documented in many areas of the Tibetan Plateau. Regional differences in glacier change across the Tibetan Plateau are evident. Measured glaciological, meteorological and hydrological data are largely absent due to difficult excess of the remote areas. Only few and spatially dispersed mass balance studies have been conducted to date. Remote sensing presents thus preferable methods in order to monitor Tibetan glacier change. In this thesis the Moderate-resolution Imaging Spectroradiometer (MODIS) snow product and MODIS Level 1 radiance Swath Data is used to derive snow line altitudes. The snow line altitude at the end of the ablation period provides a proxy for the equilibrium-line altitude (ELA) of a glacier. The variability of the annual ELA itself is a valuable proxy for the variability of glacier mass balance. The mass balances of different glaciers in a specific region often show very high correlations in their temporal variance even though the transient snowline elevation can vary across individual glaciers. In this thesis the former three facts are utilized to derive daily regional snow line altitudes and interannual ELAs on different glacierized regions distributed across the Tibetan Plateau. The regions of interest are the Western Nyainqêntanglha range, three areas in the mountains of the Transhimalayas, the Gurla Mandhata massif in the western Himalayas, the Muztagh Ata in the Pamirs, the Ulugh Muztagh ice cap in the Kunlun Shan and the Purogangri ice cap in the central eastern part of the plateau. The variability of the ELA is used to reveal differences in glacier response to the various climatic forcings.Validation and comparison of results are conducted utilizing Landsat images and a modelling approach. The derived transient snow lines are used to fit the physical based COupled Snowpack and Ice surface energy and MAss balance model (COSIMA) in order to derive energy and mass balance components on a monthly basis. The high resolution atmospheric model data from the High Asia Refined dataset (HAR) is used to correlate ELA variability and to force the COSIMA model.Results show a distinct spatial pattern of average ELA proxy with lowest altitude in the Pamirs dominated by westerlies. Average ELA on the TP is remarkably higher. A tendency towards a generally ascending ELA and more negative MB in the last decade is apparent at the Western Nyainqêntanglha range. A distinct negative MB is modelled for Ulugh Muztagh in the Kunlun Shan between 2008 and 2010. The remote sensing fitted usage of HAR forced COSIMA appears feasible for the analysis on a monthly or annual basis. Sublimation is favoured by rising temperatures, even during periods with temperatures well below freezing point, especially under arid conditions. Results further confirm the essentially different climatic patterns due to large scale circulation and local factors. Whereas, for example, increased westerly air flow in November enhances sublimation at glaciers in the east and central Plateau, it is the driver of increased snowfall in the Pamirs leading to a contrasting regional pattern of ELA variability. Strong southerly flow in July is connected to higher temperatures and is correlated with an increased ELA in most of the study regions. Monsoonal influence is traceable in regions in the Himalaya and Transhimalaya between June and September. El Niño in spring (summer) is connected to a lower (higher) ELA in the Pamir (western Himalaya). In February or March a positive phase of NAO is connected to higher wind speed and a lower ELA at many studied regions.The thesis contributes to a further and detailed understanding of the spatially differencing characteristics of climate forcing of the glaciers on the Tibetan Plateau. It serves to increase the knowledge on the current status of glaciers and cryosphere-atmosphere interaction to estimate their evolution in the future on the Tibetan Plateau. Such results are essential for further improving research on glacier related water availability in Tibet.