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Universität Giessen (2014)

Development of a high resolution permafrost distribution model in the Aksu catchment, Central Tian Shan

Imbery, Stephan

Titre : Development of a high resolution permafrost distribution model in the Aksu catchment, Central Tian Shan

Entwicklung eines hochauflösenden Modells zur Permafrostverbreitung im Aksu Einzugsgebiet, Zentraler Tian Shan

Auteur : Imbery, Stephan

Université de soutenance : Universität Giessen

Grade : Doctor of Philosophy (PhD) 2014

Résumé
Climate change is of great concern for the arid regions in Central Asia and significantly affects the hydrological cycle. Agricultural, social and economic development depends heavily on the water discharge from the rivers originating in the high mountains of the Central Tian Shan. While surface runoff in general is expected to increase in the short to mid term due to the melting of glaciers, little is known about the long term variations of permafrost and corresponding ground ice. Therefore, the overall aims of this thesis are (1) to identify key factors influencing the ground thermal regime, (2) to develop a local permafrost distribution model and (3) find implications for ground ice contents. The study focuses on the Aksu river, which contributes more than 70% to the overall discharge of the Tarim basin in Western China. As a first step, a dense ground temperature monitoring network is installed in an exemplary subcatchment. The temperatures are recorded hourly over two consecutive years (August 16th 2010 to August 15th 2012). Besides topographic features (altitude, slope and aspect) snow cover is identified as a key factor for both spatial and inter-annual variations of the ground thermal regime. As a second step, the monitored temperature data are used to develop an empirical-statistical permafrost distribution model. The model incorporates data derived from satellites and a Digital Elevation Model (DEM), such as Potential Incoming Solar Radiation (PISR) and altitude. The model output consists of the Mean Annual Ground Surface Temperature (MAGST) simulated with a 30 m horizontal resolution. The simulated MAGST was then classified into four likelihood groups for permafrost occurrence to create a high resolution permafrost distribution map for the whole research area.
Due to the close interaction between the glacial and permafrost environment, large water resources exist in the form of rock glaciers and ice cored moraines. Furthermore, the existence of massive ground ice was verified by direct assessments at locations with low slopes and fine grained sediments. In general, the ground ice content in the Central Tian Shan is very high, which is also confirmed by analysis of zero curtain periods at different depth of the active layer. Therefore, the results in this study clearly stress the importance of the permafrost environment for the water balance in the entire region. The reaction time of permafrost to climate change is much slower than that of glaciers and large amounts of ground ice can be preserved over long time periods.

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Page publiée le 5 novembre 2014, mise à jour le 8 janvier 2019