Das Projekt "Frozen rock walls and climate change: transient 3-dimensional investigation of permafrost degradation" wird vom Umweltbundesamt gefördert und von Universität Zürich, Geographisches Institut durchgeführt. Permafrost in European mountains has warmed by 0.5-0.8 °C in the upper tens of meters during recent decades. This effect is connected to changes in atmospheric conditions and, in view of projected climatic change, likely to intensify in the future. A temperature-dependent reduction in rock-wall stability is hypothesised as well as demonstrated in theory and laboratory experiments. The hot summer of 2003 provided additional strong evidence for the relation of rock fall and climate change via permafrost thaw. Rock faces generally react with much quicker thaw than gentle slopes, where a high ice content can absorb much latent heat and thus slow thaw processes. The effect of 2003 was probably largely related to thaw at the permafrost table, few meters below the rock surface. However, the reaction of permafrost also includes the thermal response at greater depth that is delayed by years, decades or centuries. The corresponding knowledge basis, however, is still limited and quantitative treatment of the involved processes constitutes a primary scientific challenge in high-mountain research. The most urgent topics of research are: a) the characteristics of temperature-related instability (e.g. re-analysis of events); and b) the location of sensitive and critical zones that exhibit corresponding temperature changes (e.g. delineation of potentially hazardous zones). For both, knowledge about the temperature distribution and evolution at the surface as well as in the subsurface of rock walls is required. The special challenges in this new field of research are: a) 3-dimensional heat flow in mountain topography; b) changes in surface conditions (e.g. degrading ice faces); and c) conditions in the subsurface that could result in a thermal offset causing lower mean annual temperatures at depth than at the surface. The proposed project investigates permafrost degradation in steep mountain slopes focusing on the above three challenges. Due to the complex nature and expense of measurements, the research approach concentrates on: 1) provision of appropriate numerical models to determine 3-dimensional temperature fields in the subsurface in complex topography including energy balance at the surface and heat transfer both in the snow cover and the ground; 2) model validation using data measured near the surface as well as in shallow and deep boreholes of the PERMOS-network and the European PACE-transect; 3) numerical experimentation using idealised test cases to determine the 2- and 3-dimensional effects of permafrost degradation; and 4) transfer of experimental results to real observations, all of this leading to a synthesis of findings. Most of the required models and algorithms as well as research strategies are published and available to the project together with corresponding know-how. Equally, much of the data required for validation is available at no cost and only few measurements need to be conducted within this project. (abridged text)