Urban Influences on Surface Temperatures in the Southwestern United States during Recent Decades

Trends of surface temperature at rapidly growing urban sites during the last three to five decades are compared to those at non-urban sites, temperatures at 70 kPa, and sea surface temperature at a coastal Pacific station. Significant urban heat island effects have apparently taken hold, with urban-affected temperature increases of 1 to 2°C common over this period. In contrast, the trend of the non-urban records has been distinctly smaller over this period. The urban warming appears to be predominantly a nighttime phenomenon, with minimum temperatures displaying considerably more increase than maximum temperatures. No uniform seasonal preference for this increase emerged from these stations. Because of this increase, the distribution of observed temperatures shows a marked warm bias at several of the urban sites during recent years.