Measuring, Monitoring, and Mitigating Urban Heat Island Effects Using a High-Density Urban Weather Station Network

Mitigation efforts for Urban Heat Islands (UHIs) have been the subject of various atmospheric modeling, observational, and regional policy research projects for many years. The city of Louisville, Kentucky, in particular has been the focus of such modeling studies (e.g., Debbage and Shepard 2015) and as well as targeted field studies that assess the UHI and other urban-related health hazards and evaluate mitigation efforts. The success of UHI mitigation efforts (e.g., greening, cool pavements, etc.) largely depends on accurate measurements of the UHI, including trends in its magnitude and spatial extent. While mesoscale meteorological networks (“mesonets”) work toward filling large data gaps between official weather stations located at airports, current mesonet configurations are too coarse to sample the extent and variability of urban heat. To address this lack of high-resolution meteorological measurements, a small-scale network of meteorological sensors was deployed across the county for the purpose of assessing the scale of urban heat, documenting human comfort indices in the urban core, and quantifying the effects of greening a small area within the urban core. The instrumentation primarily used for this project is the commercially available Tempest weather station from WeatherFlow. These low-cost, small sensors not only measure a suite of atmospheric variables (including ultrasonic wind speed and direction), but they also have built-in communication technology with a WiFi-enabled base station. The latter allows for data to be accessed via an app as well as uploaded to a remote location. These stations can be mounted on a tripod / pole combination or affixed to a pre-existing tower or post. The base station must be housed indoors, connected to power, and configured to access the local WiFi network. Data for each station is produced every minute by the sensor, sent to the base station, and uploaded to a folder in a cloud-based server. Two research grade weather stations are also used in this project. One research station is fixed in the urban core of the city, while the other is portable for targeted field observations. The network of sensors has two components: a county-wide scale and a park-scale. The county-wide scale consists of 5 Tempest sensors deployed east-west across the city to capture the zonal change in temperature from the heavily populated west side, through the more forested east side, and into the rural areas near the county border. Five Tempest stations were deployed across this approximately 30 km stretch over the spring and summer of 2023. The second component of the network is a high-density array across a “pocket park” (Founder’s Square) in the urban core of the city, such that six Tempest stations were deployed across a 50 m x 50 m portion of a city block. This park-scale network not only serves as an urban core node in the county-wide network, but it also captures the meteorological variation across a small site that is the target of an intense urban greening initiative, the Trager MicroForest Project. The fixed research station is located in the center of the park and serves as a baseline for the Tempest stations. The park network was installed in June and July of 2023. This presentation will provide a brief review of county-wide network results over the last 5 months of 2023. A targeted deployment during a heat wave in late summer 2023 will also be explored. During this heat wave, the portable weather station was deployed in a secured asphalt parking lot within the urban core but only a couple of blocks from the instrumented park. This deployment will support a comparison of temperature, heat index, and wet bulb globe temperature between the instrumented park and the asphalt parking lot during a span of dangerously hot days.