Question

why is air in a region dry?

Answer 1

The sea water temperature is the root cause of moisture content in ambient air.

The temperature of ocean water is different in different location of the earth.

Higher the temperature more is the water evaporation which increase moist climate and in reverse case dry air prevails.

The water circulation in ocean in different basins determines the sea surface temperature of a regions.

Along the eastern boundary of an ocean for example California , the surface currents carry cold ocean waters to warm areas, which cools the region and dry air.

On the Eastern United States, the Gulf Stream carries warm water along the coast up arctic area.

This provides the humidity or moist climate fort the East Coast.

Answer 2

because of the sea water temperature