Soil Thermal and Ecological Impacts of Rain on Snow Events in the Circumpolar Arctic

Abstract

Rain on snow (ROS) events are rare in most parts of the circumpolar Arctic, but have been shown to have great impact on soil surface temperatures and serve as triggers for avalanches in the midlatitudes, and they have been implicated in catastrophic die-offs of ungulates. The study of ROS is inherently challenging due to the difficulty of both measuring rain and snow in the Arctic and representing ROS events in numerical weather predictions and climate models. In this paper these challenges are addressed, and the occurrence of these events is characterized across the Arctic. Incidents of ROS in Canadian meteorological station data and in the 40-yr ECMWF Re-Analysis (ERA-40) are compared to evaluate the suitability of these datasets for characterizing ROS. The ERA-40 adequately represents the large-scale synoptic fields of ROS, but too often has a tendency toward drizzle. Using the ERA-40, a climatology of ROS events is created for thresholds that impact ungulate populations and permafrost. It is found that ROS events with the potential to harm ungulate mammals are widespread, but the large events required to impact permafrost are limited to the coastal margins of Beringia and the island of Svalbard. The synoptic conditions that led to ROS events on Banks Island in October of 2003, which killed an estimated 20 000 musk oxen, and on Svalbard, which led to significant permafrost warming in December of 1995, are examined. Compositing analyses are used to show the prevailing synoptic conditions that lead to ROS in four disparate parts of the Arctic. Analysis of ROS in the daily output of a fully coupled GCM under a future climate change scenario finds an increase in the frequency and areal extent of these events for many parts of the Arctic over the next 50 yr and that expanded regions of permafrost become vulnerable to ROS.

Rain-on-snow events over North America based on two Canadian regional climate models

“…This is due to future increases in rainfall frequency. These increases in the frequency and the areal extent of ROS events by the RCMs are broadly in agreement with the GCM-based studies of Putkonen and Roe (2003) and Rennert et al (2009). The RCM simulations, however, show general decreases in the ROS characteristics to the south of the future freezing line, associated with decreases in snow cover.…”

“…Therefore, it is very important to evaluate how these events will evolve in a future warming climate at regional scale. ROS events have significant impacts on various sectors such as the cold region environment and ecosystem (Putkonen and Roe 2003;Putkonen et al 2009;Rennert et al 2009;Casson et al 2010) and water resources, particularly for flood forecasting and risk management (Leathers et al 1998;Sui and Koehler 2001;McCabe et al 2007;Pradhanang et al 2013;Surfleet and Tullos 2013;Freudiger et al 2014).…”

Terrestrial processes affecting unlithified coastal erosion disparities in central fjords of Svalbard

“…This may induce changes in the terrestrial landscape surrounding the coast , with negative implications for coastal stability. An increase in rain-on-snow events during the winter season may enhance permafrost thaw through an increase in active-layer depth; nowhere is this more predominant than in the Arctic maritime climate of Svalbard (Rennert et al 2009;Westermann et al 2011). Permafrost degradation enhances coastal erosion as the ice-bonding of sediment is lost in thawing (Rowland et al 2010;Lantuit et al 2013).…”

Multi-Decadal Changes in Snow Characteristics in Sub-Arctic Sweden

“…Also, there is increasing evidence that changes in winter temperatures and snow cover can cause significant damage to animal populations (Post et al 2009), while an extreme winter warming event (less than 10 days long) in 2007 reduced the normalized vegetation index (NDVI: a proxy for plant production) by 26% in the following summer over an area of more than 1400 km 2 (Bokhorst et al 2009). Rain on snow events followed by freezing temperatures can create ice-hard snow layers in the snowpack (Vikhamar-Schuler et al 2010) which have been implicated in population crashes of Svalbard reindeer Rangifer tarandus platyrhynehus (Aanes et al 2000), Peary reindeer Rangifer tarandus pearyi (Barry et al 2007), musk oxen Ovibos moschatus (Rennert et al 2009) and small animals living under the snow cover such as lemmings Lemmus lemmus (Kausrud et al 2008). Ice crusts within the snowpack or at ground level may also result in the starvation and death of Electronic supplementary material The online version of this article (doi:10.1007/s13280-011-0164-2) contains supplementary material, which is available to authorized users.…”