Winter Rains Spell Trouble for Reindeer

SEATTLE, Washington, December 24, 2002 (ENS) - Too much rain during the winter months could be bad news for reindeer - the animals that tradition says power Santa Claus's sleigh. That is the conclusion of new research from the University of Washington, which details some of the potential impacts that global warming could have on these natives of the far northern latitudes.

Scientists have long known that rain falling on snow in the far north during winter months can play havoc with herds of hoofed animals - primarily reindeer, caribou and musk ox - that feed on lichens and mosses growing on the soil surface. During the winter, these animals must scrape away thick layers of snow to reach their food.


During the winter, reindeer scrape away thick layers of snow to find green moss underneath to eat. They need more than 20 pounds of food each day to survive. (Photo courtesy U.S. Forest Service)
But when rain falls on the snow, it can freeze into a thick, impenetrable layer of ice, keeping reindeer and other animals from food.

"You have an ice layer at the surface several centimeters thick that even a person couldn't get through without tools," said Jaakko Putkonen, a research assistant professor of earth and space sciences at the University of Washington.

Putkonen's research has shown that such an ice layer often lasts until summer, when the snow and ice melt. As global temperatures warm, it is now not uncommon for several rain on snow events to happen in the same winter.

In one recent instance on the far northern island of Spitsbergen, soil temperatures that normally stay well below freezing in winter months rose to near freezing and remained there for 10 days or so, because rainwater seeped through the snow and water pooled at the soil surface.

Finally the water froze, so soil temperatures dropped again. But the ice coating beneath the snow kept the animals from their food supply.


Assistant Professor Jaakko Putkonen (Photo courtesy University of Washington)
"I have seen soil temperatures remain at the freezing point for as long as two months because of the slowly freezing water below the thick snowpack," Putkonen said. "Even when ice layers are not impenetrable, the warmer soil surface temperatures promote the growth of fungi and toxic molds among the lichens, so the animals avoid those areas."

If the top of the snow is covered with a layer of ice that the animals can not penetrate, reindeer can damage their hooves trying to get to their food. Wild reindeer may starve, while cultivated reindeer herds rely on their human keepers for food.

"During those periods, the herders have to start bringing out hay because the reindeer just can't get food," he said.

It now appears that climate change will make things substantially worse, Putkonen said.

Putkonen has developed a model of snow and soil heat generation to gauge the effects of climate change in areas such as northern Alaska and Canada, Greenland, northern Scandinavia and Russia, and Spitsbergen, a Norwegian island midway between Norway and the North Pole.


Reindeer graze on the island of Spitsbergen, one area being affected by more rain on snow events that can cut the animals off from their food supply. (Photo Jaakko Putkonen)
The current scientific understanding of where and when rain on snow events happen is based on observations over a number of years. Putkonen used a computer model to fill in missing data between areas where observations were made.

To analyze the effects of human caused climate change, Putkonen and his colleague Gerard Roe studied the results of the global climate model for the decade of 1980 through 1989 and found that it correlated quite well with actual observations during that period.

"If anything, the model understated the results," Putkonen said.

Looking ahead to the decade of 2080-89, the model shows a 40 percent increase in the land area affected by rain on snow events. Typically those events happen closer to coastal areas, but the model predicts they will move much farther inland.

That will mean major impacts not only on reindeer herds but also on the people who depend on them for their livelihood.


Sami reindeer breeders in eastern Lapland. (Photo courtesy Destination Kiruna)
"The bottom line is that the rain will penetrate farther into the interiors of the continents, where most of the reindeer are," said Putkonen. "This is a consequence of climate change that specifically affects native peoples. They have depended on reindeer and caribou for thousands of years, but they don't have the means or the ability to deal with these effects."

Putkonen hopes this work will lead to more in depth study of how reindeer and other large ungulates, or hoofed animals, living in northern climes will be affected by global climate change. For instance, it is unclear how much the loss of food because of rain on snow events affects the animals' mortality.

So far, there is little understanding of how much greater the effect will be as those events occur farther inland, where most of these animals live, Putkonen added.

The research by Putkonen and Roe, a postdoctoral researcher in the University of Washington's Quaternary Research Center, will be published in an upcoming issue of "Geophysical Research Letters," a publication of the American Geophysical Union.