The leeward side of the mountain is the side of the mountain that is covered by wind and you may notice that that side is drier than the windward side, which is the side that faces the incoming wind.
Now the leeward side temperature increases from top to bottom because when the air goes up the mountain from the windward side, it loses most of its moisture. So by the time the air goes down the leeward side, it lacks moisture and heats up as it loses even more moisture going down. This is called the rain shadow effect.
There are 50 states of the US
Mecca receives 4.3 inches of rainfall a year, mostly in the winter months.
Answer:
It happens because the consuming is higher than the water drop rate, or even because there are too many people in a zone where there is not enough fresh water.
