The tree cooling pond effect and its influential factors: A pilot study in Gold Coast, Australia

Abstract

Residents were suffering from climatic issues resulting from global warming and urban heat islands (UHI). Researchers have explored ways of mitigating these issues. They have discovered several factors that adjust microclimate, including vegetation. Vegetation, especially trees, can significantly mitigate heat stress, often by providing canopied spaces. However, the temperature differences between various points under individual trees have rarely been investigated. The present study aimed to determine these temperature distribution patterns. A new concept, the tree cooling pond effect (TCP), was proposed and defined in a similar way to UHI. The level of TCP was represented by the mean radiant temperature (MRT) difference between four points in line with the direction of tree shade (A, next to the trunk; B, the midpoint between A & C; C, the margin of the shade; and D, 1 m away from C and in the sunshine). The MRT was measured and shown to increase slightly when moving from A to C, with a sharp increase between C and D. Physical characteristics of the trees, especially the tree crown diameter (TCD), impacted the incremental change (∆MRT) significantly. Through linear regression, it was found that ∆MRT was polynomially correlated with tree characteristics; e.g., TCD and distance from the trunk. For a tree with a TCD of 16.6 m, the ∆MRT between Point A and Point D was up to 18 °C; this result indicates that trees had insignificant cooling effects on the unshaded area (in the sunshine) despite neighbouring it. This study represents an initial effort; it visually illustrate tree cooling by identifying several critical points to delineate the pond, which has rarely been considered in previous studies.

Keywords

• Tree cooling pond effect
• Temperature distribution
• Canopy
• Crown diameter
• Outdoor thermal environment