Temporal Variability In The Daytime Green Roof Energy Balance During Drying Periods

Green roofs are a building design element intended to increase evaporative cooling in cities during the summer, which helps alleviate the daytime impacts of heat on human health and energy consumption, and supports mitigation and adaptation to the local effects of climate change. Time varying energy balances were measured on a 0.15 m deep, ~ 60 m2 modular green roof with Sedum spurium in London, Ontario for the summer of 2014. A lysimetry approach was used to measure latent heat QE. Net radiation Q* and ground heat flux QG were also measured, with sensible heat flux QH derived as a residual. An empirical model of evaporative flux ratio QE/(Q*-QG) by volumetric water content VWC was fit based on experimental data (typical values ranged from 0.2-0.4 and decreased linearly to 0.05 during atypical low VWC below 0.22). Research presented here can inform future optimization of green roof atmospheric cooling performance. Furthermore, this study indicates that green roof atmospheric cooling performance in typical North American mid latitude climates is lower than typical urban greenery such lawns and parks, which has policy implications for sustainable building design and urban planning