Extreme winter conditions on the Mongolian steppe has been causing extensive die-offs of sheep, goats, cattle, and camels — animals that traditional herding communities rely on for their survival.

Severe winters that kill large numbers of livestock are common enough in Mongolia that there is a local term for the phenomenon — dzud. But  now, the dzud has been occurring more frequently and getting worse.

People in Mongolia’s Uvs province believe that overgrazing and changing climate are exacerbating the problem. “We used to have four seasons, but now we only have three. Before, June, July, and August were warm and with rain. Different types of grass would grow, and the animals would get fat. Now, we have no rain and the wind dries up the grass, say locals.

This is a threat not only to livestock, but to the nomads’ way of life: Bereft of the animals they rely on for food and income, hundreds of thousands of herders have streamed into the country’s capital of Ulaanbaatar, hoping to find work. Finding solutions is complicated by the fact that dzud is difficult to predict, since the conditions that give rise to the disaster are hard to pin down.

Between 1940 and 2015, an official ‘dzud declaration’ was made a dozen times, and the phenomenon has killed more than 20 million animals since 2000. While excessive winters might have previously occurred once every decade or so, they are now happening every year in the steppe.

As a land-locked, semi-arid region, Mongolia’s year-to-year rainfall and temperature are notoriously variable. The recent dry spell is unusual compared with the last thousand years. Due to frequent high-pressure systems, rainfall tends to drop off significantly.

While scientists struggle to find the cause of dzud, the herders are developing strategies to keep themselves afloat. If marmots and other local rodents go to ground early, the nomadic herders know a harsh winter is on the way. They then reduce winter mortality by proactively culling old and weak animals from their flocks, and fattening the remaining herd by moving them to places where grass is more abundant. Now it is becoming increasingly difficult to forecast. In the wake of worsening dzud, some communities have been working more collectively by collaboratively culling herds, preparing winter feedstock, and planning pasture rotation schedules to give overgrazed areas a chance to regenerate.