TREAT: Tipping points and resilience of mountain permafrost

Alpine permafrost, as found in the European Alps, is undergoing major changes due to climate change. At several sites, temperature sensors located in boreholes demonstrate an increase in the subsurface temperature. The warming of the subsurface increases the depth at which we can find frozen rocks as well as the loss of subsurface ice, which in turn may result in rock falls and mountain collapses posing a potential threat to infrastructure and human life. The expected further increase in global surface temperature together with the occurrence of extreme temperature events, such as heat waves or droughts, demand a better understanding of the distribution of ice in the subsurface and the thawing rates. Direct measurements of ice content in the subsurface provide only information at the position of the drilling and can only be conducted after drilling, which means it can only be performed once at a given location. Geophysical methods do not have this limitation; thus, offer a possible alternative to understand the extent of ice in the subsurface and to monitor its changes over time. Geophysical measurements provide 2D and 3D images of the subsurface indicating changes in the physical properties of the rocks and soils, which can then be interpreted in terms of ice content. Nonetheless, to date there is no universal law that permits to convert geophysical data into ice content. In this project, we propose a series of activities that should permit to obtain variations in temperature and ice content from geophysical monitoring measurements. In particular, we plan to advance the modeling tools used for the interpretation of geophysical images in terms of water and ice content. We plan to apply these novel tools for analyzing existing records from the European Alps, as well as for new monitoring data sets. Based on our analysis we aim at answering critical questions, namely: (a) whether mountain permafrost will become wetter (due to additional water input from melting ground ice) or drier (due to direct drainage of the melt water and enhanced evaporation under climate warming), (b) whether substrate-specific tipping points exist leading to irreversible permafrost thaw and (c) which landforms are most resilient to climate warming, and may therefore play a significant future role for regional hydrological systems.