Abschlussarbeiten
Cryosphere Variations in Different Climatic Regimes and its Impacts Using Geomatics
Art der Abschlussarbeit
Habilitation
Autoren
- Bolch, Tobias
Betreuer
- Prof. Dr.phil.habil. Manfred Buchroithner
Abstract
Glaciers are typical elements of the mountain cryosphere and are key indicators for assessing climate change in remote mountain areas where climate stations are rare or non-existent. Glacier run-off can be an essential source of freshwater especially during summer and early autumn when the water demand is usually highest. Water release from permafrost bodies can also play an important role especially in arid areas. Since the end of Little Ice Age, a nearly global recession of the glaciers with an accelerating trend in recent decades is noticeable. Glacial lakes can develop and expand concomitant with glacier recession. Outbursts of these lakes can represent a serious threat to the infrastructure and society downvalley. Hence, assessing the cryospheric variations is of uttermost importance. However, glaciers are usually situated in remote and rugged mountain regions which are difficult to access. Remote sensing, GIS analysis and modelling are therefore ideal means to study glacier fluctuations and their impacts. A perquisite for these investigations is a precise digital terrain model (DTM) and suitable remote sensing imagery. Clean ice is relatively easy to map using multi-spectral imagery. Debris-cover, however, which is common for many glaciers of the world, hampers the automated mapping. Own analysis revealed that a combination of morphometric and thermal information leads into promising results for larger debris-covered glaciers. Slope was identified as the key parameter for this task. The uncertainties of the mapping approaches are, however, too large for change assessments and manual adjustment is required. A glacier inventory can be generated within less than one year for large areas such as western Canada with more than 15’000 glaciers based on remote sensing if suitable imagery and previous glacier outlines are available and the area of debris-covered glaciers is limited. Early declassified imagery from the 1960s and 1970s such as Corona and Hexagon are valuable sources for extending the remote-sensing based glacier analysis back in time and to evaluate previous inventories based on topographic maps from similar years. Glacier area and length changes represent indirect signals of climate variability only while glacier mass balance shows the most direct signal. Multi-temporal DTM comparisons allow the glacier mass balance to be estimated. Own investigations showed that stereo Corona is also a valuable source for the generation of precise DTMs for this task despite image distortion and unstable camera parameters. Multi-temporal DTMs from different sources such as ASTER, aerial images or Cartosat-1 data allow the generation of a mass balance time series. However, tilts and inaccuracies in absolute elevation of the generated DTMs or the use of different software packages require careful relative adjustments in order to minimize the uncertainties. Almost all glaciers showed a significant and continuous recession in all investigated regions in western Canada and high Asia in the last decades despite different climatic controls. The identified recessions were, however, less than previously published based on topographic maps. I could also show that the glaciers at Mt. Everest clearly lost mass despite thick debris cover. However, the mass loss is within the range of the global mean. A case study about rockglaciers in the Tien Shan based remote sensing and terrain analysis provided some insights into their occurrence and characteristics. The spatial distribution of rockglaciers is to a certain degree related to the distribution of glaciers and the availability of debris. The permafrost bodies contain also a significant amount of ice which can be of importance for the run-off. Geomatics was also proven to be an effective tool to assess the developments and to provide a first order classification of the potential danger of the glacial lakes. The current and future availability of high resolution imagery and DTMs will allow similar investigations with higher accuracy which will lead to an improved understanding of the reaction of the cryopshere to changing climate and its impacts.
Zugeordnete Forschungsschwerpunkte
- Geoinformationssysteme für Umweltmonitoring
- Kartographie mit Radaraufnahmen
- Fernerkundungskartographie
Schlagwörter
cryospheric variations, glacier, change of climate
Berichtsjahr
2012