Quantifying the cooling effects of urban trees in relation to their growth

Over the last few decades numerous research have shown that urban greening can mitigate urban heat island and adapt our cities to climate change. In fact, the cooling benefits of trees are caused by two main factors. First, the canopies of trees provide shade, reducing the input of short wave radiation to ground level, particularly in the summer when deciduous trees are in leaf. Second, trees, like all plants get rid of the accumulated heat by conduction, convection and transpiration – the latter being the largest process of heat loss if soil water is available. Through this transpiration process trees cool them down and reduce the amount of heat available to warm the air around them. Largely due to the higher latent heat of vaporization and specific heat, the process of evapotranspiration is particularly effective at generating high evaporative cooling. However, the growth and performance of different tree species grown at heterogeneous and harsh growth conditions in urban areas is so variable that we lack quantitative estimates of just how effective they are. Therefore micro-scale studies on tree growth and eco-physiology are absolutely necessary for these quantitative estimates. The project choose contrasting tree species in terms of ecology and tree anatomy grown at different street canyon conditions (building height to width ratio) to continuously measure tree transpiration, tree growth and morphology, bio-meteorological and edaphic variables between April 2015 and March 2018.The continuous data will help us to have better estimates of tree cooling effects in terms of surface and boundary layer air cooling not only spatially but also temporally.