Extreme Weather
Warmer temperatures across the Arctic are increasing the frequency of extreme weather such as rain-on-snow events and wildfires, affecting the ability of reindeer and caribou to access adequate vegetation.
Rain-on-Snow Events
As the climate changes, the frequency of extreme rain-on-snow (ROS) events is increasing. Rain falling on snow freezes, creating ground ice that accumulates in thick layers and covers plants, rendering them inaccessible for reindeer and caribou that cannot dig through these "ice-locked pastures" (Hansen, et al,. 2011).
Researchers in Norway found that warmer and wetter winter climate is contributing to an increase in intense ROS events in Svalbard. Using temperature and precipitation models, they estimated the probabilities of ROS events and found large increases in these probabilities in areas covered by vegetation. According to their models, these probabilities will only continue to increase in the future. As the number of ROS events increased, the proportion of ice-locked pastures also increased, and the population growth rates of Svalbard reindeer decreased (Hansen, et al., 2011).
Hansen, et al., 2011
Hansen, et al., 2011
In November of 2013, a large ROS event left an ice layer several inches thick, causing 61,000 reindeer on the Yamal Peninsula in Russia to starve in 2013 and 2014 (Guarino, 2016). Warmer temperatures are leading to early retreat and thinning of sea ice in the Barents and Kara Seas, causing increased precipitation and a greater chance of ROS events occurring in the autumn and winter (Forbes et al., 2016).
30,000 indigenous Yamal Nenets live on the peninsula, 6,000 of whom are reindeer herders, migrating 1200 km annually between lichen woodlands in the summer and shrub-graminoid tundra in the spring, summer, and autumn. Warmer, wetter winters causing more frequent and intense ROS events pose challenges for this nomadic way of life. In 2013 and 2014, herders who lost their reindeer to starvation where forced to turn to subsistence fishing (Guarino, 2016). Nenets may also have to begin herding smaller, more privately owned herds rather than large collective herds (Forbes, et al., 2016).
Extreme snow itself is also reducing forage availability. Caribou and reindeer must expend a lot of energy digging through deep, hard snow to access lichens beneath. According to Sami reindeer herders in Finland, ice layers and mold were the most significant causes of their largest reindeer losses. Thick snow that falls over unfrozen soil and lasts the whole winter can promote mold growth on winter pastures, causing reindeer to avoid the areas. Furthermore, some of these fungi produce mycotoxins that may have physiological and behavioral consequences on reindeer. The changing climate could alter the range of these fungi and their ability to produce mycotoxins (Turunen, et al., 2009).
Boreal Forest Fires
An increase in the number of forest fires in Alaska and Canada pose challenges for local caribou populations. In Alaska, half of the years with the most severe fires in the past 60 years have occurred since 1990, and two of the three most extensive fire seasons occurred within the last ten years. In the winter, migrating caribou graze in late successional habitats in the boreal forest or boreal tundra interface - areas containing abundant, mature lichen cover, which provides a high energy source and reduces the need for caribou to rely on body stores (Gustine, et al., 2014). After a fire, it can take over 50 years for lichen to grow back to an abundance that can support caribou, and some lichen species take even longer. Therefore, once an area is burned, it can remain unable to support caribou for decades (Mallory & Boyce, 2017).
Researchers in Alaska modeled future fire regime characteristics in the winter ranges of two caribou herds in the Alaskan-Yukon Arctic. They found that winter caribou habitat, especially for herds that winter primarily in the boreal forest, will become increasingly susceptible to forest fires in the future due to the expansion of shrub=dominated tundra and warmer temperatures. The images show the relative flammability of the region using a warm (left) and a hot (right) global circulation model (Gustine, et al., 2014).
Gustine, et al., 2014
Huge forest fires are also burning in other parts of the Arctic. In 2019, Siberian taiga forests burned for over three months (Cormier, 2019).