Thousands of Mongolian herders face disastrous livestock losses from a dreaded severe weather phenomenon known as the "dzud", the Red Cross said Thursday in launching an international emergency aid appeal.

Landlocked Mongolia is grappling for the second straight year with dzud conditions -- a dry summer followed by brutal winter cold that leaves livestock and other animals at risk of starvation and exposure on the country's rugged steppes.

It threatens tens of thousands of herders in a country where almost half the population depends entirely on livestock for food, transportation and income, the International Federation of Red Cross and Red Crescent Societies (IFRC) said.

Cattle, sheep and other animals usually die en masse in the dzud, weakened by insufficient summer grazing that prevents them building up the fat reserves necessary to withstand winter temperatures as low as -50 degrees Celsius (-58 degrees Fahrenheit).

"In spring, animals give birth and when the livestock are already exhausted from the winter they are at high risk without adequate feed, shelter and veterinarian care, which does not exist in some remote areas," Nordov Bolormaa, secretary-general of the Mongolian Red Cross said at a press conference.

As of early February, more than 42,546 livestock had perished in the current dzud, she said, citing official Mongolian figures.

Launching its appeal in Beijing, the Red Cross said the figures were expected to grow "exponentially" with the full impact likely only becoming clear by May.

More than a million animals died in the 2015-16 dzud.

The Red Cross estimated that currently more than 157,000 people are "at risk" this year across 17 of Mongolia's 21 provinces.

- Climate change -

Among them is Munkhbat Bazarragchaa, a herder in a remote region who has lost 10 of his 60 livestock animals.

Heavy snows also have prevented him and his wife from travelling to see their two sons, who are away at school, since October.

"This winter has been harsh which means in the spring it will also be very difficult," he said in a video released by the ICRF.

The footage showed him hauling the stiff carcasses of goats and a dog gnawing on a dead cow.

He said his family would use any cash assistance they receive to purchase flour and rice, plus hay and other fodder for the animals.

The dzud typically used to occur only once every 12 years, but now appears roughly once every four years, with climate change suspected in the increased frequency, the Red Cross said.

A 2009-2010 dzud brought the most severe winter in memory, leaving dead, frozen animal carcasses strewn across the plains.

At least eight million livestock animals died, according to official estimates.

- 'Inherited from our ancestors'-

Thousands of Mongolia households live as nomadic herders amid Mongolia's vast plains and mountains, and recurring dzud conditions are blamed for forcing many into a marginalised urban existence near the capital Ulan Bator.

The relief organisation hopes to raise enough to assist 11,000 of the hardest-hit herders, including provision of cash grants, first-aid kits, and funds to help communities prepare for future dzuds.

During the winter of 2015-16, many people sold off their live animals, causing a market oversupply that depressed prices and hurt many vulnerable small herders, said Gwendolyn Pang of the IFRC in Beijing.

She said "many will lose their livelihoods and will have no choice but to migrate to slum areas" outside Ulan Bator or other urban centres.

For herder Bazarragchaa, that would be unthinkable.

"This way of life is inherited from our ancestors and has been practised for thousands of years," he said. "I can't imagine Mongolia without animals."