Modeling past, present, and future basal ice amounts in the snowpack at a High Arctic site

Winter snow is a key factor affecting many aspects of polar ecosystems. Snowpack thickness, and ice layers formed within and, particularly, at the base of the snowpack, have all been linked to fluctuations in High Arctic animal populations in Svalbard. In northwestern Svalbard, measurements of snow properties have been made along a series of transects around the peninsula Brøggerhalvøya annually since 2002. Measurements are made over a 1-2 day period in April/May, with soundings made at 100-200 m intervals along transects, and snow pits dug at regular intervals to determine the snowpack stratigraphy, in particular the basal ice layer thickness. In 2010, 2012 and 2015, extreme winter warm periods, with temperatures well above freezing, led to the formation of a pervasive ground-ice layer, whose average was 10 cm thick or more across low-lying terrain around the peninsula. Here we present the results from a model used to simulate the winter snowpack and, more importantly, the development of the ice layer at the base of the snowpack. The model couples a surface energy balance model to a multilayer snow model simulating vertical evolution of density, temperature and water content, accounting for percolation, refreezing, storage and water runoff, and to a soil model to simulate heat conduction beneath the snowpack. Forcing is provided by data from nearby meteorological station data, and covers the period 1969-2016. The model is calibrated to the snowpack measurements around the peninsula, and is able to successfully simulate the significant icing events of the past decades, both those measured since 2002 and earlier events that were noted by biologists working in the area. We evaluate the development of the winter snowpack under future climate warming scenarios by performing a temperature sensitivity analysis. We rerun the model holding all meteorological forcing parameters constant except for temperature. We adjust temperature non-linearly to simulate the changes observed in the 47-year meteorological record, in which there is a larger increase in colder (i.e. winter) temperatures compared to warmer (i.e. summer and winter warm event) temperatures. Our modeling suggests that in a future warming climate, winter snowpack basal ice formation will occur more regularly, but that the frequency of major events will decrease.