Quantifying the impact of vertical greenery systems (VGS) on Mediterranean urban microclimate during heat wave events

Abstract

This research investigates the potential of vertical greenery systems (VGS) to modulate the outdoor microclimate in a real-scale Mediterranean climate street canyon with respect to a non-vegetated control during four heat waves and summer conditions. The cooling effect of VGS on air temperature was assessed using an identical set of sensors in both canyons. The effect on thermal comfort was evaluated using radiation fluxes, Mr.T tool, and the ENVI-met model that was validated against measured data.

The VGS cooling effect during the heat waves was up to 0.36–2.04°C, and its duration was significantly extended. The correlation (R² = 0.75) between the cooling effect, relative humidity, and wind direction, highlights that warmer and drier conditions increase the VGS cooling effect during heat waves.

VGS improved the mean radiant temperature (T_mrt) above the canyon (3.9–4.1°C) and at the pedestrian level (2.21–2.8°C), while the physiological equivalent temperature (PET) and universal thermal climate index (UTCI) decreased by an average of 0.67–1.07 °C and 0.63–0.8 °C, respectively. Shaded walls improved the average T_mrt (11.7°C), PET (3.2°C), and UTCI (2.7°C), reflecting the importance of casting shadow in the urban environment.