Modeling Transient Three-dimensional
Temperature Fields in Mountain Permafrost
My PhD thesis deals with transient 3-dimensional modeling of subsurface temperatures in steep terrain for the investigation of the distribution and evolution of mountain permafrost.
An abstract of my thesis is provided here: [english] [deutsch]
The objective of this thesis is to describe and analyze mountain permafrost in greater depths (i.e., below the active layer), with a main focus on its three-dimensional distribution and transient effects from past and possible future climate variations. For this purpose, we designed a modeling procedure that includes the processes in the atmosphere, at the surface, and in the subsurface, and which is based on the combination of existing approaches.
The results indicate a three-dimensional distribution pattern of mountain permafrost, which is mainly influenced by topography and spatially and temporally variable surface temperatures. Isotherms incline steeply and strong lateral heat fluxes exist, which minimizes the influence of the geothermal heat flux. Transient signals from past climate variations in current permafrost temperatures derive mainly from the last glacial period and the major fluctuations during the past millennium. Temperature depressions in high mountains are smaller than in flat terrain, because multi-lateral warming in steep topography accelerates the pace of a surface temperature signal intruding into the subsurface. Simulations of future conditions point to subsurface temperature fields that substantially deviate from stationary conditions and are characterized by deep-reaching and long-term perturbations, generally rising temperatures, and an increase in both volume and vertical extent of warm permafrost zones. In the European Alps, near-surface permafrost on steep south-exposed slopes will have disappeared even in the highest peaks within the next two centuries, but substantial permafrost volumes will remain at depth for centuries to millennia.
Three-dimensional and transient modeling tools are important for the comprehensive analysis of mountain permafrost conditions, since in complex mountain topography near-surface conditions do not provide sufficient information. For future research the influence of variable surface and subsurface characteristics on the subsurface thermal field, the interpretation of temperatures recorded in boreholes in mountain topography, and the re-analysis of past rock fall events from permafrost slopes are important topics.