Simulating the thermal regime and ice mass balance in blocky terrain in mountain environments

Ground temperatures in coarse, blocky deposits such as in mountain blockfields and rock glaciers have long been observed to be lower in comparison with other (sub)surface material. One of the reasons for this negative temperature anomaly is the lower soil moisture content in blocky terrain, which decreases the duration of the zero curtain in autumn and can introduce a zero curtain in spring. Many permafrost modelling studies did not include varying water and ice contents. In this thesis, the CryoGrid community model is used to simulate the effect of drainage in blocky terrain on the ground thermal regime and ground ice at two Norwegian mountain permafrost sites and at three ancillary sites in the global permafrost extent. Three idealized stratigraphies are used to investigate thermal anomalies under different amounts of snowfall. The stratigraphies are labeled blocks only, blocks with sediment and sediment only and are either drained or undrained of water, resulting six ‘scenarios’. The model setup features a surface energy balance, heat conduction and advection, a bucket water scheme with a lateral drainage component and (an adaptation of) the CROCUS snow scheme. The results show markedly lower ground temperatures in the blocks only, drained scenario compared to all five other scenarios. A sensitivity analysis to snowfall results in a thermal anomaly is up to 1.5 °C at the sites in Norway for scenarios with relatively high snowfall amounts and up to 3.5 °C at a continental site in northern Siberia. The effect almost vanishes when no persistent ground ice is present. Stable permafrost conditions are simulated at the location of a rock glacier in northern Norway with a mean annual ground surface temperature (MAGST) of 2.0-2.5 °C in the blocks only, drained scenario. Other scenarios under the same climate forcing feature positive ground temperatures. At the location of a blockfield in southern Norway, it is shown that stable permafrost can be present in the blocks only, drained scenario even under an extremely thick snowpack. Under (semi-) arid conditions, the rate and timing of subsurface drainage is also strongly affected by the ground stratigraphy. The drainage starts earlier in summer, continues longer in autumn and is of higher magnitude in the blocks only stratigraphy, compared to blocks with sediment stratigraphy. Finally, transient simulations at the rock glacier site in northern Norway showed a complete or partial lowering of the ground ice table since 1951 for all scenarios except for the blocks only, drained scenario. The drainage effect that was simulated herein helps explain the occurrence of permafrost in coarse, blocky terrain below the assumed elevational limit of permafrost. It is thus important to consider this effect in future permafrost distribution mapping and thermal modelling. An accurate prediction of the evolution of the ground ice table in a future climate has implications for slope stability as well as water sources in arid environments

The CryoGrid community model (version 1.0) - a multi-physics toolbox for climate-driven simulations in the terrestrial cryosphere

The CryoGrid community model is a flexible toolbox for simulating the ground thermal regime and the ice-water balance for permafrost and glaciers, extending a well-established suite of permafrost models (CryoGrid 1, 2, and 3). The CryoGrid community model can accommodate a wide variety of application scenarios, which is achieved by fully modular structures through object-oriented programming. Different model components, characterized by their process representations and parameterizations, are realized as classes (i.e., objects) in CryoGrid. Standardized communication protocols between these classes ensure that they can be stacked vertically. For example, the CryoGrid community model features several classes with different complexity for the seasonal snow cover, which can be flexibly combined with a range of classes representing subsurface materials, each with their own set of process representations (e.g., soil with and without water balance, glacier ice). We present the CryoGrid architecture as well as the model physics and defining equations for the different model classes, focusing on one-dimensional model configurations which can also interact with external heat and water reservoirs. We illustrate the wide variety of simulation capabilities for a site on Svalbard, with point-scale permafrost simulations using, e.g., different soil freezing characteristics, drainage regimes, and snow representations, as well as simulations for glacier mass balance and a shallow water body. The CryoGrid community model is not intended as a static model framework but aims to provide developers with a flexible platform for efficient model development. In this study, we document both basic and advanced model functionalities to provide a baseline for the future development of novel cryosphere models