Coupling heat flux dynamics with meteorological conditions in the green roof ecosystem

Green roofs can notably modify the thermal properties of the building envelope and adjacent air to bring environmental benefits. This study investigates the heat flux dynamics of the tropical green roof ecosystem to provide a scientific basis for design and management. Green roof experimental plots were established to monitor the total solar radiation, net radiation, and micrometeorological parameters. The data permit calculation of sensible and latent heat fluxes using the Bowen ratio energy balance (BREB) method. The results demonstrated the life cycle characteristics of heat flux components. The dynamic changes of sensible (H), latent (λE) and soil (G) heat fluxes were denoted by single-peak quadratic curves. Net radiation (R_n) was largely determined by quantity and variation trends of λE, reaching at 1300 h a maximum λE of 655 W m^-2 and maximum H of 369 W m^-2. Temporal heat-flux fluctuations were strongly correlated with meteorological variables. Extreme values of H and λE correlated well with precipitation and temperature (R² = 0.78). Dynamics of heat-flux magnitude and partitioning demonstrated notable differences by daily and season periods. They displayed considerable variations in flux partitioning, with Bowen ratios strongly correlated with weather conditions and vegetation types. The energy budget of the green roof ecosystem is unbalanced with a heat loss of about 15.5% caused by soil and canopy heat reserve. The passive indoor cooling effect under the green roof is attributed to the unbalanced energy closure.