Why is eastern region climate milder than Western region climate of Nepal

Due to the geographic location along the equator, and Greenwich meridian

The climate of the West is semi-arid, yet parts of the region get high amounts of rain or snow. Other parts are true desert which receive less than 5 inches (130 mm) of rain per year. The climate is unstable, as areas that are normally wet can be very dry for years and vice versa.