Impacts of Urban Tree Canopy and Water Features on the Thermal Environment

Impacts of heat stress within an expanding hot desert city include: increased heat-related illnesses and mortality, increased water and energy use, and decreased use of outdoor spaces for activity. Concerns associated with these compounding factors are of great importance in Tempe, Arizona. The strategic implementation of trees and water features in open urban settings can moderate thermal stress by intercepting incoming solar radiation and repartitioning available energy to latent heat. The objective of this study is to assess the impacts of urban trees and the presence of water features on the urban micro-climate and human thermal comfort (HTC). Five 90-minute transects using a human bio-meteorological platform (MaRTy) were completed on June 22nd, 2018 between 10:00 and 20:00 MST to gather meteorological variables that help quantify the thermal environment and HTC. The largest contributor to HTC in semi-arid climates is mean radiant temperature (sum of longwave and shortwave radiation). Findings indicate that provision of tree shade decreases mean radiant temperatures by ~20ºC when placed over concrete and grass surfaces. Although water is lower in temperature than the surrounding environmental air temperature, it is less effective than tree canopy at reducing mean radiant temperatures and ambient temperatures. Our results provide useful guidelines for improving the thermal environment for urban inhabitants by demonstrating the relative thermal and radiative impacts associated with tree coverage and water features in a semi-arid environment.