Reference data for actual evapotranspiration in a Mediterranean green roof: Evidence from a monitored green roof system in Genoa, Italy

Study region: This study investigates the evapotranspiration of a monitored green roof installed in Genoa (Italy) characterized by Mediterranean coastal climate. Study focus: Accurate estimation of actual evapotranspiration (AET) and moisture dynamics remains a challenge to fully assess the hydrological performance of green roof systems (GR). This study investigates the AET rates of a GR using high-resolution observation of microclimatic and soil moisture data with a daily water balance model. AET rates are determined for 21 dry weather periods spanning 18 months of a continuous monitoring program. Observed daily AET rates are compared with reference evapotranspiration (ET0) rates determined through a modified FAO-56 Penman-Monteith model by introducing a linear soil moisture extraction function and considering the role of GR system and vegetation with a crop coefficient (Kc). New hydrological insights for the region: Examination of AET data indicates that for GR with an abundant soil moisture level, AET is initially driven by energy (temperature and net radiation) but as the moisture decreases during a dry weather period, the soil water availability is mainly driven AET. Kc of 0.89, is estimated through minimization of percent bias for prediction of AET during dry weather periods and provides good AET predictions even if the seasonal trend produces overprediction in warm periods and underprediction in cold periods. Future studies will elucidate seasonal Kc values accounting for the vegetation growth dynamics.