Transient and Transition Factors in Modeling Permafrost Thaw and Groundwater Flow

Diel variations in chemical and isotopic compositions of a stream on King George Island, Antarctica: Implications for hydrologic pathways of meltwater

Antarctica is highly susceptible to climate and environmental change. In particular, climate change can lead to the warming of permafrost and the development of active layers in permafrost areas, resulting in variations in hydrological characteristics. This study investigated the hydrological process associated with a stream in a snow-dominated headwater catchment on King George Island, maritime Antarctica, during austral summer using the chemical and isotopic compositions. During the cold period, as the snowmelt rate decreased, the amount of new water also decreased. Hence, the electrical conductivity (EC) increased because the contribution of supra-permafrost groundwater ("old" water), which occurs in the active layer, increased more during the cold period than during the warm period. Moreover, diel variations in the stable isotopic compositions (δ¹⁸O and δD) of snowmelt ("new" water) were clearly observed in the stream water, indicating that runoff was the dominant flow path of snowmelt during the cold period. In contrast, during the warm period, the amount of snowmelt increased and the EC value decreased as a result of the dilution effect. In addition, compared with the cold period, diel variations in the isotopic compositions of the stream water were attenuated during the warm period. This attenuation effect was not due to the increased contribution of old water; instead, it was due to the contribution of new water with a low-amplitude signal in the diel variations of the isotopic compositions. Thus, the observed diel variations in the isotopic compositions of the stream water during cold and warm periods suggest that this catchment is dominated by new water. These findings are helpful for improving our understanding of climate-related changes in the hydrological pathways and water-related ecosystems of polar catchments.

Rain, Snow and Frozen Soil: Open Questions from a Porescale Perspective with Implications for Geohazards

Climate change is already affecting high mountain regions, such as the European Alps. Those regions will be confronted with a significant rise of temperatures above the global average, and more and heavier rain events, also during wintertime. The system response to the coincidence of rain, snow, and possibly frozen soil depends on the almost infinite number of possible combinations of thermo-hydraulic states of the involved phases. Landslides, snow avalanches, debris flows, or extensive surface runoff are just a few of the possible hazardous outcomes. With rising temperatures and increased precipitation, those hazardous outcomes are expected to occur even more frequently in the future, requiring a better understanding of those coupled processes for hazard mitigation strategies. The macroscopic phenomena are controlled by porescale processes, such as water freezing and ice grains blocking pores, which are only barely understood. The strong coupling between thermal state and hydraulic parameters, the possible phase change, and material heterogeneity pose great challenges for investigation. This work provides an overview of documented hazard events regarding rain, snow, and possibly frozen soil. The current state in theoretical and experimental research is presented before several knowledge gaps are derived and possible techniques to address those gaps are discussed.