The arid climate of the southwestern U.S. is primarily influenced by the rain shadow effect and its latitude.

The arid climate of the southwestern U.S. is largely shaped by the rain shadow effect and the region's latitude. The rain shadow effect occurs when moist air from the Pacific Ocean is blocked by mountain ranges, like the Sierra Nevada, preventing rain from reaching the region. As a result, areas in states like Arizona, New Mexico, and Nevada receive minimal rainfall and experience desert-like conditions. Additionally, the region's southern latitude exposes it to intense sunlight and warmth, further contributing to its dry climate. These factors combine to create the arid conditions found in the southwestern U.S.