Evapotranspiration rates and evapotranspirative cooling of green façades under different irrigation scenarios

Abstract

Urban population growth has resulted in land use changes and the replacement of many vegetated areas with hard surfaces that have a higher heat capacity than vegetation and have negatively impacted the urban microclimate. Green façades are a method of reintroducing vegetation into city landscapes to help remediate the urban hydrological cycle closer to predevelopment conditions by improving evapotranspiration. This study quantifies the impact of green façade irrigation regimes on evapotranspiration rates and evapotranspirative cooling effects across the day. Rates of evapotranspiration were calculated from façade’s water balances, under sunny, dry weather conditions with three different irrigation regimes. In this experiment both non-deciduous native (Australian) and deciduous non-native (non-Australian) plant species, with two different façade orientations were used to explore their evapotranspiration rates and impact on evapotranspirative cooling. Evapotranspiration rates were lower under limited-watered conditions for the north-facing green façade, planted with non-Australian plants, followed by the normal-watered and well-watered conditions. In the west-facing green façade that was planted with Australian plants (known to thrive with minimal irrigation), the lowest evapotranspiration rates were recorded for normal-watered, followed by limited-watered, and well-watered scenarios. The highest evapotranspirative cooling of the green façades occurred under well-watered conditions, with an observed maximum evapotranspirative cooling of −4.4 °C and −1.7 °C for the north- and west-facing façade. The results highlighted the ability of Australian waterwise plants to transpire more (both evapotranspiration rate and diurnal evapotranspiration) and provide more evapotranspirative cooling under normal and limited-watered conditions. The findings from this study will contribute to more effective design of sustainable green façades, with recommendations relating to irrigation rates and plant species.