Quantifying How Rain on Snow Events Change Snowpack Properties Using Caribou and Muskoxen as Test Cases

Rain-on-snow (ROS) events - when rain falls on a cold snowpack, freezes, and creates a hard ice layer - are increasing in frequency across the Arctic. These events have dramatic and far-reaching impacts on the Arctic system for humans, society, infrastructure, wildlife, ecosystem function, soil, and vegetation. An assessment of the physical impacts of ROS events on snow and ice properties is urgently needed as the Arctic system warms rapidly and climate regimes shift at unprecedented rates. This project will assess and quantify the effects of ROS events on Arctic snowpacks through a combination of snow and ice field measurements, historical ROS observations, and the development of an ice-layer model (IceLayer) that quantifies ROS ice layers formed in snow. IceLayer will be used to identify thresholds in key snow and ice properties that influence winter mobility and forage accessibility for caribou and muskoxen. These species are a central component of Arctic systems, because human communities and ecosystems depend on them culturally, environmentally, and economically. Despite growing concern regarding major Arctic system impacts resulting from ROS events, we lack methodologies to quantify and evaluate the effects of ROS on the snowpack (e.g., melting snow and subsequent ice layer formation on top, within, or below the snowpack). This project will quantify how ROS events modify snow and ice properties at spatiotemporal scales relevant to Arctic system processes, to produce information on ice-layer formation, thickness, snowpack position, and strength resulting from ROS events. This project will use the most widely applied snow modeling system in the world, SnowModel, and extend and enhance its current capabilities to simulate ROS-induced ice-layer formation and associated snowpack property changes, including ice layer location within the snowpack, thickness, strength, timing, duration, and areal extent, across space and time. To guide model development, researchers will collect field observations of ROS-induced snowpack changes in Alaska, Canada, Greenland, Svalbard, and Finland, and collate historical records of ROS observations across the Arctic. The scope of this project will include Arctic land areas and snow environments inhabited by two wildlife species that are currently exposed to and directly impacted by ROS events: caribou / reindeer (Rangifer tarandus) and muskoxen (Ovibos moschatus). To ensure the benefits of IceLayer are as useful as possible for different audiences, this project will include an outreach event for youth in rural western Alaska, a snow and ice field measurement workshop for collaborators, a scientific workshop on using the IceLayer model, and a hybrid meeting to provide IceLayer to interest groups, citizens, and professionals concerned with the societal impacts of ROS events. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.