Spatial and temporal characteristics of the Casa Grande, Arizona urban heat island

The urban heat island is a commonly studied phenomenon where city size, wind speed, and cloud cover, as well as surface thermal properties all play a role in its intensity, which is highest 3-5 hours after sunset. In this study, the spatial and temporal aspects of the heat island in the small arid city of Casa Grande, Arizona are investigated. Temperature and dewpoint data were collected through a combination of fixed stations and two mobile transect routes on four separate nights during a period of ‘ideal’ conditions conducive to strong urban – rural temperature differences, consisting of clear skies and light winds from 15-18 March 2004.

A mobile transect on 18 March revealed a maximum heat difference of 4.7°C along the east to west route, with a spatially interpolated temperature map illustrating warmest areas in the far eastern commercial corridor and cooler areas in the far southern and western regions of the city, consisting of rural agricultural fields. Wind speed measured at the Casa Grande Municipal Airport (KCGZ) during transect times was seen to be a factor in determining the intensity of heat differences. However, due to very light wind conditions encountered on all three nights (<2.5 m/s), surface thermal properties and land use may have played the largest role in determining the greatest heat island experienced in the city. Thermal imagery taken of the area at a time similar to transect times (2125 LST) confirms the idea that surface thermal properties may play a large role in determining heat island characteristics near the ground with the absence of strong winds, with warmest temperatures reflected on south-facing slopes of nearby mountain ranges and coolest temperatures reflected off of irrigated agricultural fields.