Multidimensional factors affecting tree-induced cooling benefits: A comprehensive review

Planting trees is regarded as an effective solution to urban heat challenges in urban planning, design, and management. However, several emerging studies have reported conflicting results. Rethinking tree planting is essential for urban heat mitigation and adaptation. Therefore, this study aims to delineate factors affecting tree-induced cooling benefits (TICBs) from biological, physiological, functional, configurational, geospatial, morphological, and managerial perspectives. This review delineated these perspectives in terms of tree traits, planting methods, and environmental context. Accordingly, methods to improve TICBs are pinpointed into tree traits and planting methods tailored to the surrounding environment. Priorities include broad-leaved species, large trunk circumferences, tall shapes, low branch point heights, wide and large crowns, umbrella-shaped shapes, large leaf area density, simple leaves, hairy leaves, small leaves, low stomatal resistance, and diffused pores. The planting spacing, row, density, and species diversity should be increased. Trees are favorable in hot and arid climates with low wind speeds, and permeable or reflective pavements beneath trees are recommended. Building density and street orientation also controlled the expected TICBs. In waterfront and greenery areas, trees should be designed with water bodies and green open spaces. TICBs depend on shading and evapotranspiration, where water availability is a premise for maintaining normal physiological processes, growth, and survival of trees. Finally, this study updates research directions to enhance TICBs. Overall, this study can assist urban planners, designers, and managers in making appropriate decisions on planting trees for urban heat mitigation and adaptation.