A heat dome is baking Arizona and Nevada, where temperatures have soared past 115 degrees this week and doctors are warning that people can get third-degree burns from the sizzling asphalt.

At Lake Mead, which supplies water for 25 million people in three southwestern states and Mexico, water levels have plunged to their lowest point since the reservoir was filled in the 1930s. In California, farmers are abandoning their thirstiest crops to save others, and communities are debating whether to ration tap water.