'Urban island' heat tests Phoenix and other large cities

PHOENIX, Arizona - When temperatures soar as they have this week in downtown Phoenix, homeless people ride the air-conditioned light rail to avoid a heat so brutal it killed 155 people in the city and surrounding areas last year. 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. Phoenix on Wednesday recorded a sweltering 46 C, setting a new high for the date.

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