Regional settlement patterns are most affected by this physical characteristic.

Land and water and air.

Explanation:

The physical characteristics that would affect the settlement in its regional settings is the natural landscape that composes the land, water, and air and other biotic and the abiotic contents amount which the quality of the natural resources such as the crops and the Agri system of a region depends on the nature of the terrain and the fertility of the soil and the availability of the freshwater for the irrigation and the purpose of drinking.

The main physical characteristic affecting regional settlement patterns in the Middle East is water.