Because of the rainshadow effect, . a dry region occurs on the downwind side of a mountain a dry region occurs on the windward side of a mountain rainfall fluctuates, arriving in equal amounts on both sides rainfall varies, but always falls in shadow areas the wet region is determined by the location of jet stream

Because of the rain shadow effect, a dry region occurs on the downside of a mountain.

Option: A

Explanation:

In orographic rainfall, mountain acts as barrier and moisture laden wind get an obstacle in its path in the form of that mountain and cause rainfall in the windward sides of the hills (mountain) and create rain shadow region in the lee ward sides of the hills (mountain).

Because when moisture laden winds reach that side all the moisture in the winds dries up. For e.g. eastern part of western ghat mountain in the Peninsular India is an example of rain shadow region.