It's good to have giant shade trees, these provide many benefits for areas that have problems with water conservation. Shade Trees attract water to the area, the more closed in with foliage the roots are the easier it is for the ground to maintain moisture.
Trees naturally lower the air temperature by the process of evaporation from the leaves, lowering the temperature of the leaf, then lowering the temperature of the air around the leaf. Forests and Jungles can create collumns of cool air that can be 40 degrees colder than the surrounding atmosphere.
As a result, rain occurs when warm, humid air passes over these collumns of cold air, quickly condensing the water-saturated air into precipitation.
The solution to arid environments is plant more trees.