Global warming is threatening Siberian reindeer and the nomadic herders who depend on them by turning snow to impenetrable ice, scientists say.
Autumn rainfall can prove catastrophic for the deer when freezing temperatures return in winter, creating a crust of hard ice several centimetres thick that covers the grass the animals feed on.
When snow lies on the ground the deer are able to root through it and find sufficient food to last the winter.
Two extreme episodes of icing in 2006 and 2013 caused mass starvation among reindeer herds in western Siberia.
Scientists have now linked both to thinning sea ice and higher humidity in the Arctic Barents and Kara seas as more water escapes into the atmosphere.
Heavy ice crusts following rain are said to be having "long-term and serious" effects on about 6000 Yamal Nenets, among the last truly nomadic reindeer herders in the Arctic.
Study leader Professor Bruce Forbes, from the University of Lapland, said: "In a normal year, crusted snow patches are common, but herds can be relatively easily led to nearby areas with softer snow.
"The reason the 2013 event was so catastrophic was that heavy rains saturated much of the snow cover from top to bottom, so when air temperatures plummeted the pastures were frozen beneath a thick, heavy layer of ice. This left animals locked completely out of pastures across the entire southern Yamal Peninsula, an area covering some 27,000 square kilometres."
During that year, 61,000 reindeer died - more than a fifth of the total Yamal Peninsula population of 275,000.
Such events were increasing in severity, according to the researchers whose findings are reported in the Royal Society journal Biology Letters.
The scientists interviewed 60 herders and administrators in the region between March 2014 and April 2016 to build up a detailed record of how herding had changed over several decades.
The rain-leading-to-ice events were found to occur about once every 10 years.
