Mark Serreze

There is increasing recognition that Arctic rain on snow (ROS) events are becoming more common with significant and sometimes even catastrophic impacts on the physical and living environments of the North. These events are generally associated with short-lived warm spells in autumn and winter, linked to extratropical cyclones that generate rain, followed by a rapid drop in temperature leaving an icy crust. Rain on snow events can foster avalanches, influence snow structure, warm underlying permafrost and increase the depth of the permafrost active layer. Rain on snow events influence population dynamics of lemmings, voles, and bird species that seek shelter in the snowpack. Icing may lead to a fading of lemming cycles, causing crashes of Arctic predators such as the snowy owl and Arctic fox, which depend on them. In marine environments, polar bears and ringed seals are also impacted. Perhaps the most devastating impact of ROS events, however, is that ice layers, in creating barriers that prohibit foraging, can lead to massive die-offs of large herbivores, with concomitant socioeconomic impacts, especially in regions where humans depend on reindeer for food, transportation, and other needs. The international Arctic Rain on Snow Study (AROSS), a project within the National Science Foundation’s Navigating the New Arctic (NNA) initiative, seeks to better understand the distribution, severity, and changes in the frequency of rain on snow and melt-refreeze events in the Arctic and their impacts.