There is less precipitation than normal, A drought is caused by a change in the normal weather patterns. The sea level will rise due to global warming, this redistributes the currents so there won't be the normal weather there. Because there is very low precipitation due to the high pressure of air the water level will drop making the ground harder and dryer meaning trees and other plant life can't grow there.
Credits:
Created with images by NASA Goddard Photo and Video - "Black Marble - Asia and Australia" • Moyan_Brenn - "Desert"