A Study of the Oklahoma City Urban Heat Island Using Ground Measurements and Remote Sensing (Formally Paper 2.1)

We compare temperature measurements taken in Oklahoma City during July from a moving vehicle, at fixed locations above ground, and from a satellite platform. Oklahoma City is a medium sized city (population = 500,000) with a relatively small built-up downtown core. It is not clear whether an urban heat island (UHI) would develop in OKC, especially given the strong winds that exist there. During the Joint URBAN 2003 experiment a van was driven on several different routes at night through the city and out to rural areas. In addition, there were a large number of temperature measurements taken around the clock on elevated platforms by numerous groups. Finally, 90 m resolution remotely sensed surface temperature images of the Oklahoma City area were obtained from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER).

Our initial analysis of the vehicle transects indicate that a UHI does form at night in the range of 1 - 5 C. Also of note were temperature changes of several degrees that occurred over distances of blocks within the downtown core. These were usually associated with abrupt changes in underlying land use (e.g., a normal built-up street transitioning to a one-block vegetated park). In the near future, we will also include the stationary temperature measurements in our analysis, and try to ascertain the impact of ambient wind conditions on the strength of the UHI.

Currently, only the daytime thermal image has been analyzed. It shows the downtown core surface temperatures being up to 8 degrees C warmer than the surrounding rural areas. Because these are skin, not air, temperatures, this is not indicative of an urban heat island during the day. Shortly, we intend to analyze the nighttime thermal image and compare these with the air temperatures measured during Joint URBAN. The hope is that by better understanding the nature of the urban heat island, we can then better model the wind fields over a city and produce better airborne contaminant dispersion calculations.