Final answer:
The dryness of Manang and Mustang is primarily due to the rain shadow effect of the Himalayas, where the mountain range blocks precipitation, leading to arid conditions in these regions.
Step-by-step explanation:
The dry and cold conditions of Manang and Mustang can be attributed to the rain shadow effect caused by the Himalayas. Much like the Andes creating dry conditions for the Atacama Desert, the Himalayas block moisture-laden clouds, causing precipitation to fall on the southern slopes facing the Indian Ocean.
This leaves the northern side, where Manang and Mustang are located, with significantly reduced precipitation. The air loses its moisture as it ascends the mountain and descends into these areas, becoming warmer and drier, which further inhibits rainfall, leading to the arid conditions experienced throughout the year.