An occasional siren wails as paramedics rush to help people sick from the heat.

Already devilishly hot for being in the Sonoran desert, Arizona's largest city is also an "urban heat island," a phenomenon that pushes up temperatures in areas covered in heat-retaining asphalt and concrete. Forecasters said the high for Phoenix had risen to 111 degrees (44 Celsius) by midafternoon Thursday and was not expected to hit Wednesday's record high for the day of 116.

Phoenix officials say they are tackling urban warming, monitoring downtown temperatures, planting thousands of trees and capturing rainwater to cool off public spaces.