Modulation of Diurnal Cycle Ranges by Decadal Variability and Outer Urban Expansion

We report and analyze temperature changes induced by combined effects of urban expansion and modulation caused by decadal variability. These changes are identified from observations at three stations representative of highly, moderately urbanized and rural regions. The magnitude of the diurnal range over the urban stations undergo a persistent long-term decrease driven by urbanization, that is more pronounced in Phoenix and relatively nonexistent in the rural station. The diurnal range continues to decrease in Phoenix despite the fact that urbanization has reached saturation in the neighborhood of the observation site. In addition, the time series show intricate decadal variations, which appear to be remarkably correlated and unrelated to urbanization. Furthermore, mesoscale simulations demonstrate that distant urbanization contributes to the rate of change of the diurnal cycle over Phoenix.