The correct answer is: Heavy snowfall.
Ladakh is a high-altitude desert region in the Indian Himalayas. It is one of the coldest inhabited regions in the world, with an average temperature of -5°C. The region receives heavy snowfall during the winter months, which can make it inaccessible to travelers.
Excessive rainfall is not a major problem in Ladakh, as the region receives very little rainfall. Landslides are also not a major problem, as the region is not prone to earthquakes. Floods in the Indus river are also not a major problem, as the river is not very wide in Ladakh.
Therefore, the only option that is a major problem in Ladakh during the winter months is heavy snowfall.