The seasonal microclimate trends of a large scale extensive green roof

At nearly 27,500 m², the Jacob K. Javits Convention Center (JJCC) located in New York City, hosts one of the largest extensive green roofs in the United States. This paper explores three years of fine scale microclimate data collected at the JJCC green roof and its potential ability to reduce the urban heat island intensity (UHII). Surface energy fluxes and microclimate parameters on four different surfaces are analyzed before and after installation of the southern section of the green roof, offering a unique before/after, test/control study. The results indicate that the temperatures of the air above the green roof, and its exterior surface are different (e.g. lower) than those measured above and on, respectively, the black roof that preceded it. Differences in the maximum daytime air and surface temperature between the black and green roof were 1.80 °C and 18.4 °C, respectively. Installation of the green roof increased evapotranspiration, modifying the roof's surface energy balance, and reduced the median summer nighttime UHII (compared to the pedestrian level station) by 0.91 °C. Though microclimatic conditions on two sections of the green roofs vary somewhat, the research findings generally support the statement that green roofs are a moderately effective strategy for mitigating the UHI effect.