Numerical modelling of convective heat transport by air flow in
permafrost-affected talus slopes
Abstract. Talus slopes are a widespread geomorphic phenomenon in the Alps. Due to their high porosity a gravity-driven internal air circulation can be established which is forced by the gradient between outside (air) and internal (talus) temperature. The thermal regime is different from the surrounding environment often leading to cold microclimates and permafrost occurrences. So far this phenomenon has mainly been analysed by field studies and only few explicit modelling studies of this phenomenon exist. Numerical simulations of permafrost sometimes use parameterizations for the effects of convection, but mostly neglect the influence of convective heat transfer in air on the thermal regime. On the contrary, in civil engineering many studies were carried out to investigate the thermal behaviour of blocky layers and to improve their passive cooling capacity. The present study further develops and applies these concepts to model heat transfer in air flow in a natural scale talus slope. Modelling results show that convective heat transfer has the potential to develop a temperature difference between the lower and the upper part from about 0.7 °C (boundary closed to the atmosphere) to 2.5 °C (boundary open to the atmosphere). A seasonally alternating chimney-effect type circulation develops. Modelling results also show that this convective heat transfer leads to a cold reservoir in the lower part of the talus slope which can be crucial for maintaining the frozen ground conditions under climate change.