Many cities are looking to green infrastructure as an innovative, cost-effective way to reduce energy consumption, manage storm water runoff, and obtain ecological and social co-benefits. Green infrastructure (GI) refers to high-performing green spaces that provide important services to the human environment. It is known that urban vegetation cools land surface temperatures during the day, however uncertainties remain regarding the magnitude of microclimate variation due to GI. 24 TidbiT temperature loggers were deployed to obtain replicate measurements of air temperature (Ta) within about three city blocks to explore variability of the temperature response both within and between green streets (having one or more GI features) and grey streets (the absence of any GI). Green street deployment consisted of eight TidbiTs in a bioswale, two in a city park block area, and two in Portland State University’s bioswales. An additional 12 sensors were deployed in grey streets. Two adjacent streets were chosen as the main grey street study location, with 90% and 55% average impervious surfaces in a 10-meter radius from the TidbiT centroid, respectively. The TidbiTs recorded temperatures every 15 minutes for 29 days.
Results/Conclusions
Maximum daily temperatures for green street sensors averaged 30.1 ºC, while grey streets averaged 32.2 ºC. The data show an average difference of 2.2 ºC during the hottest part of the day (5:00-6:00 pm), when the cooling benefits are most needed. From 11:00pm to 7:00am, green streets are up to 0.4 ºC warmer than the grey streets, revealing a night-time moderating effect of GI. Sun exposure on grey streets was consistently higher than green street locations, supported by the 46% decrease in vegetation coverage within a 10-meter radius. Complementary data on sun exposure and vegetation cover reveal the importance of collecting auxiliary data on the local environment to better understand the deployment area. Stratifying greenery based on 50-square-meter pixels (in a larger, multi-city study) does not guarantee the temperature sensor deployment location will be representative of an area of the appropriate vegetation density. This study has highlighted a need for further specification of green infrastructure features: park blocks, bioswales, community garden, grey street, etc. Future assessments aim to complement research done with the Urban Water Innovation Network (UWIN), (NSF #1444758), in hopes of quantifying how urban GI influences microscale Ta patterns.