The Department of Civil and Environmental Engineering presents the Environmental and Water Resources Engineering Seminar Series and 2022-23 AEESP Distinguished Lecturer Cliff Davidson of Syracuse University for “The Green Roof as a Complex System,” Thursday, Feb. 3 at 11 a.m. in the Willa Cather Dining Complex Pioneer Suite or PKI 160.
About the presentation: As cities grow and modify the natural environment, many municipal governments have recognized the benefits of installing green roofs and other types of green infrastructure. Green roofs can reduce combined sewer overflow, minimize flooding, decrease the intensity of the urban heat island, flooding, decrease the intensity of the urban heat island, and provide habitat for urban wildlife.
We consider how the performance of a green roof can be modeled and measured in an effort to understand its benefits in built-up urban areas, using the instrumented extensive green roof on the Onondaga County Convention Center in Syracuse, N.Y. We examine two general categories of performance, energy flow and storage, and water flow and storage.
In the first category, the soil and vegetation that make up the green roof can dissipate heat much more quickly than concrete and other building materials, reducing high temperatures that can impact people's health and damage urban ecosystems. By installing temperature sensors in the various layers of a green roof during its construction, we can produce thermal profiles as a function of time that can aid in estimating the heat flow through the roof. This is examined in mid-summer when the plants are fully grown and the building is air conditioned, and in cold temperatures in winter when the vegetation is dormant, both with and without a blanket of snow.
Other factors such as soil moisture can also impact heat flow through the roof. Regarding water flow and storage, the soil of the green roof can hold stormwater until evaporation as well as transpiration by the plants can remove it. The total rate of water loss, known as evapotranspiration, influences the time it takes for the roof to recharge its water-storing capacity after a rainstorm. By conducting a water balance on the roof, we can understand the complexity of factors that influence how much incoming rainwater flows down the roof drains and how much is retained by the soil and vegetation to evapotranspire slowly over time.
Finally, we attempt to explain why some cities have moved forward with many green infrastructure projects, while other cities have preferred traditional gray infrastructure. A separate tutorial will be available on the capabilities of a new website showing real-time data and archived data from the Onondaga County green roof. The website is intended for use in the classroom to help students understand the physical processes taking place on a green root and the functions of a green roof.