Simulation of schoolyard's microclimate and human thermal comfort under Mediterranean climate conditions: effects of trees and green structures.

The present study explores the effects on microclimate parameters and on heat stress conditions of the bioclimatic redevelopment of an urban schoolyard based mainly on inserting shading canopies and replacing hard surfaces with green cover. This included the use of the recent version of the microclimate model ENVI-met (V4), first validated using experimental data and then later applied to different case studies in schoolgrounds of Volos, a coastal city in central Greece under Mediterranean type climate. The simulation of the existing yard condition showed that the values of the biometorological index PET (physiologically equivalent temperature, in °C), were within the range of the thermal sensation class of extreme heat stress (> 41 °C) from early morning, while at midday 80.5% of the yard area was within the range of the above class. With the implementation of the redesign proposal, 69.9% of the yard area was improved by two or three PET scale classes, helping to improve the microclimate in 82% of the total area of the courtyard. Tree canopies reduced the direct incident radiation more than 90%, reduced Tmrt and PET index up to 31 °C and 19 °C, respectively, and the surface ground temperatures of wet grass and hard surfaces more than 20 °C and 14 °C, respectively.