Why one part of the earth's surface is arid and dry and a nearby part is lush and wet is explained by the term?

The process that explains why one part of the earth's surface is arid and dry and a nearby part is lush and wet is areal differentiation. It is an approach to geography that shows the dependence of the distribution of physical and human phenomena and the relation  to each other from the physical location. Areal integration on the other hand is the approach that studies how places interact with each other.