Urban effects on the diurnal temperature cycle in Phoenix, Arizona

Abstract

Empirical estimations of urban effects on the diurnal temperature cycle were carried out for Phoenix, Arizona, through a framework capable of estimating the mean urban effect on air temperature. The analysis of pre-urban and urban differences in hourly temperature data at Sky Harbor International Airport during dry tropical conditions in June and January revealed a significant urban influence. Minimum temperature was most influenced by urbanization with the mean minimum temperature during the urban period exceeding that of the pre-urban period by 4.4°C (2.4°C) in June (January). A significant urban heat sink in January maximum temperatures was evident as the mean maximum temperature during the pre-urban period exceeded that of the urban period by 1.5°C. The greater thermal inertia due to urban growth around the airport and the growth of the airport itself has also had an effect on nocturnal cooling rates. Pre-urban January minimum temperatures typically occurred between 06:00 and 07:00 local standard time (LST) in the pre-urban period and between 07:00 and 08:00 LST in the urban period. Similarly, in June, the minimum temperature occurred on average around 05:00 LST during the pre-urban period and between 05:00 and 06:00 LST during the urban period. This apparent decrease in cooling rates was modeled well by the first harmonic fit to the average hourly temperature data.