Tree Architecture and Urban Microclimate


Urban Forestry / Research / Tree Architecture and Urban Microclimate

Tree Architecture and Urban Microclimate

The mitigation of climate change impacts such as warming is increasingly urgent in urban environments, which already struggle with higher temperatures caused by the urban heat island effect. Trees and greens spaces play a critical role in the mitigation of air temperatures (both absolute and in terms of personal thermal comfort) in urban environs, through reflection and absorption of irradiation, transpiration cooling and shading. The known norms for temperature reduction of trees however, are relatively broad (eg. cooling ratings ‘high’, ’medium’, or ‘low’). Variables such as crown shape, crown transparency, branch and stem structure vary significantly from species to species, aspects elaborated in work done around ‘tree architecture’. Leaf shape, total leaf area (index), foliage period and leaf colour may also impact cooling values. Insights into these variables in relation to the cooling performance of various tree species is the primary objective of this project. Insights into which aspects of a tree’s ‘architecture’ impact on these differences is an extended objective.

Research Design

Cooling Performance of tree configurations

A related question is the cooling performance of trees in various configurations. Most urban trees form part of group plantings such as tree lines, avenues, bosques and groves etc. These configurations have potentially significant effects on the level of heat island mitigation in both absolute terms and in relation to auxiliary factors such as urban typo-morphology, prevailing wind directions, humidity & surfaces and other features in urban spaces. Of these, the focus is on the testing of configurations in typical typo-morphological situations such as squares, streets and parks. In this regard the project can/should involve multiple sites and or cities.


Drought tolerance of tree spp.

Other climate change impacts in urban environments include extreme drought and/or flooding. Limited underground areas for tree roots to draw moisture and large areas of hard surfaces which exacerbate flooding add to these problems. More precise data on the moisture demand of different species (= drought tolerance) in limited sub-surface conditions is thus a secondary research goal. Data should reveal the relative moisture efficiency of tree species, as compared to their absolute drought tolerance (for instance Quercus spp. are considered drought-tolerant trees but need a relatively large subsurface area for their root system to survive dry periods).