Reduction of apparent temperature under urban trees in a hot-humid green area

Abstract

A thermo-hygrometric analysis was carried out at 9, 12 and 16 hrs, under six groups of urban tree species with different levels of shading, plus a lawn as control area, on a hot and humid day of November 2018 in Campos dos Goytacazes, Rio de Janeiro. Air temperature and relative humidity data were converted into apparent temperature heat indexes (HI). The results obtained were subjected to analysis of variance and, if significant, a regression analysis was performed. Shading indexes were calculated using five fisheye photos taken under each group of tree species, in order to obtain a mean sky view factor (SVF) for each location. Values of SVF and HI of each different evaluation time were subjected to Pearson’s correlation analysis. There was a significant difference within the groups of trees at the three evaluation times. The maximum HI (43.91°C) was recorded at midday. On the lawn area, there was a significant positive correlation between the SVF and the HI at different evaluation times, and it was higher at noon. Increased sunlight exposure, due to decreased sky blockage, causes a significant increase in HI.

Keywords

• sky view factors
• thermal stress
• urban parks
• urban silviculture