Frank Paul and Max Maisch

Department of Geography, Glaciology and Geomorphodynamics Group, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland

Glacier changes are among the clearest natural indicators of climatic changes (Haeberli et al., 1998). In particular changes in glacier length are easy-to-follow witnesses of past and ongoing climatic variations and their shifting trends. In contrast to the glacier mass balance, which is the direct and undelayed reaction to the yearly meteorological conditions, length changes display an integrated behaviour, reflecting climatic conditions (mainly temperature and precipitation), in a long-term pattern persisting over many years. Thereby, length variations are an enhanced and, due to glacier motion from the accumulation to the ablation zone, filtered and delayed signal that depend on glacier size and geometry as well as on various other specific topographic factors. Thus, cumulative length changes reflect various frequencies of short-term, decadal or even centennial magnitude (cf. Fig. 86.1).

In Switzerland changes in glacier length have been measured annually since the 1880s, starting with large, long and easily accessible glaciers. At the moment data of about 120 glaciers are collected every year within the framework of the Swiss length measurement network. In particular medium-sized glaciers reflect decadal climate oscillations quite well, as visible from Fig. 86.1. Figure 86.1 also depicts the maximum extent at the end of the Little Ice Age (around 1850-1860) and a general recession period since then, interrupted by two intermittent phases of read-vance in the 1920s and 1970s (1965-1985). A similar pattern of glacier fluctuations has been observed around the globe (e.g. Hoelzle et al., 2003). Apart from direct measurements documenting changes in glacier length, much effort has been put into the reconstruction of former glacier extent from indirect evidence, such as lateral moraines (geomorphological approach), or ancient maps, historical paintings and chronicles. In the Alps in recent decades several detailed studies on the historical evolution

In addition to spaceborne optical data, the GLIMS project intends to increasingly utilize the integration of solar reflective, thermal and microwave remote sensing to assist in glacier analysis, thereby addressing the limitations of multispectral approaches. This is a key future direction of the GLIMS project.

of individual glaciers and larger mountain groups have been completed. Zangl & Hamberger (2004) illustrate photographically the striking glacier retreat of many Alpine glaciers during the past 100 yr.

By extending the existing Swiss inventory backwards in time a thorough documentation (presenting extensive statistical analyses) of Swiss glacier changes is given by Maisch et al. (2000). They have shown that from 1850 to 1973 the entire Swiss glacier area was reduced by more than 25% and glacier volume has shrunk by one-third in total. In most of the mountain regions that typically have a majority of small glaciers, the volume loss was 50% or even more. At the same time a nearly 100 m rise in the equilibrium line altitude (ELA) was calculated, with a regional tendency to higher values in the drier parts of the southern Swiss Alps. The most recent assessment from satellite data has shown that the Alpine glacier area has decreased by another 20% from 1985 to 1999 (Paul et al., 2004).

In order to manage the challenges and needs of worldwide glacier monitoring in the 21st century and with regard to utilizing glaciers as key elements in global climate related observation programmes (Haeberli et al., 1998), modern digital methods are developed for glacier monitoring. These procedures are based on:

1 digitizing of historical and recent glacier outlines from topographical maps in a geographical information system (GIS);

2 combination with a digital elevation model (DEM) to obtain three-dimensional glacier inventory parameters (e.g. slope, aspect);

3 automated delineation of glacier outlines from multispectral, high-resolution (ca. 20 m) satellite imagery (e.g. Paul et al., 2002; Kaab, this volume, Chapter 85).

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Figure 86.1 Cumulative changes of glacier length measurements from 1850 to 2003 for eight differently sized glaciers in the eastern Swiss Alps. Whereas the largest glaciers depicted (e.g. Morteratsch) reflect only low-pass-filtered and long-term climate changes, medium-sized glaciers indicate decadal fluctuations (e.g. Tschierva) and small glaciers reflect annual or stochastic variations (e.g. Paradisin). (Data source: Swiss Glaciological Commission of the SCNAT (Swiss Academy of Science).)

Figure 86.1 Cumulative changes of glacier length measurements from 1850 to 2003 for eight differently sized glaciers in the eastern Swiss Alps. Whereas the largest glaciers depicted (e.g. Morteratsch) reflect only low-pass-filtered and long-term climate changes, medium-sized glaciers indicate decadal fluctuations (e.g. Tschierva) and small glaciers reflect annual or stochastic variations (e.g. Paradisin). (Data source: Swiss Glaciological Commission of the SCNAT (Swiss Academy of Science).)

Figure 86.2 Oblique perspective view of the Bernina region (eastern Swiss Alps), using a high-resolution satellite image from 1997 (IRS-1C) and glacier outlines from 1850 (white) and 1973 (black) draped over a DEM with 25m spatial resolution. (DEM: © swisstopo (BA 04622).)

The synergetic use of these three techniques (satellite, GIS, DEM) enables impressive visualizations of both the Alpine mountain scenery and the ongoing glacier retreat (Fig. 86.2). Future applications of the digital Swiss glacier inventory and related digital data sets will include: numerical modelling of glacier changes and their relation to climate change, application of distributed glacier mass balance models (e.g. Klok & Oerlemans, 2002) over large mountain regions as well as the forcing of such models with output from regional climate models to determine the impact of past or future climatic conditions on mountain glaciers.

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