Can urban farms help to reduce the urban heat island?
The urban heat island (UHI) refers to the temperature difference that often occurs between urban and rural areas: cities can be as much as 3oF warmer, on average, than non-urban areas (occasionally cities are as much as 5-6oF warmer). Among the most important factors contributing to the UHI is the lack of vegetation and the high amount of impervious surface in cities as compared to rural areas. Actively growing vegetation and pervious soils help to cool the environment by using solar energy for evapotranspiration rather than for heating the air, and trees provide shade that helps to keep temperatures cooler near the ground. Heat-island mitigation strategies often focus on urban greening via installation of green roofs, pervious pavements, and adding parks and trees. Urban farms, however, have so far been overlooked in terms of their potential to ameliorate the UHI.
This project aims to determine whether and how much urban farms might help to reduce urban heat islands. To do so, we are measuring air temperature and humidity at and around Frogtown Farm prior to, during, and following the development of the farm. We hope to document how this change in land use and land cover may affect the localized UHI in the Frogtown neighborhood. Temperature and humidity are being measured at five locations: at the farm itself and in four locations in the surrounding neighborhood. The image at right shows the approximate area covered by the sensors, with the diamond showing the approximate location of the Frogtown Farm sensor (for privacy, neighborhood sensor locations are not identified). Weekly graphs of temperature and humidity (dew point) at the Farm and neighborhood locations are available on the web at https://sites.google.com/a/umn.edu/klink/ff_uhi.
Taking into account the elevation difference between the farm and the surrounding neighborhood, preliminary analyses show that the Farm was, on average, about 0.24oF cooler than the neighborhood during the summer (late June through late August, 2014) and about 0.09oF cooler than the neighborhood during the winter (November 2014 through February 2015). During the summer, for some hours of the day the temperatures at the Farm were as much as 2.8oF cooler than in the neighborhood. Cooler temperatures at the Farm might be expected given that the site was dominated by grass cover, whereas the surrounding neighborhood is a mixture of grass, trees, gardens, asphalt streets, concrete sidewalks, houses, and light industry; all of these non-vegetated surfaces, as well as car, bus, and truck traffic, contribute to the urban heat island.
For more information about the Frogtown Farm UHI project, please contact Kathy Klink at firstname.lastname@example.org or 612-625-3452.