The Urban Heat Island
The mechanisms which lead to the creation of an urban heat island (UHI) have been studied for nearly a century and are well understood. Like many other large cities, the PMA has a substantial UHI. As early as 1921, urban effects on the local climate in Phoenix, Arizona were recognized. Analyzing winter-time minimum temperatures in the Salt River Valley, Gordon (1921) found that the weather station in Phoenix, which at the time was roughly two percent of its current population, was warmer than expected for a low-valley location. He noted that the Riverside Nursery is protected on the north by both the diversion of the cold air stream and by the city of Phoenix itself with its warming influence likely making him the first scientist to describe the Phoenix UHI. Since that time, the population has increased nearly 40-fold, resulting in an intensification and expansion of the UHI.
Muller says that UHI isn’t important. With only eight degrees of urban nighttime warming, pin head alarmists are surprised that we don’t have as many record lows as we used to.
As a long-time Phoenix resident, I can attest to UHI here in the city, especially during our hot, dry, sunny summers. I actually live south and east of Phoenix in the suburbs, and enjoy measuring the UHI. I wait until just about sundown, mount a temperature sensor outside my car, (load up my doggies – they love car rides) and drive a circular loop down to the Indian reservation and then back up to the city.
During the summer months, I average about 7 to 8 degrees delta T cooler out on the open prairie compared to the urbanized areas. It is also generally more humid out of the city limits. When I drive back to town, the temperature reflects it by going back up to just about where it was when I started even though by that time the sun has completely set.