Abstract Summary
Due to climate change, urban heat-stress is increasingly becoming a risk to health, the livability and accessibility of public spaces (Klok & Kluck, 2018). Trees are often mentioned as best measures to solve heat-stress by providing cool spots or routes (Gromke et al., 2015; Spanjar et al., 2022). However, little is known about the cooling potential and relationship between tree characteristics such as canopy width, height or foliage cover. These characteristics can be negatively influenced in urban areas by limited rooting depth, too much shade or poor soil conditions, which potentially reduce the cooling potential of a tree. Especially during warm periods in summer - the moment when cooling is most desired - trees suffer from drought and leaf fall (reducing foliage cover). In this research trees with different characteristics and health conditions were measured on a densified square in Amsterdam during three hot summer days (at least >25 °C and no clouds). To estimate the Physiological Equivalent Temperature (PET), 5-hour (12:00-17:00) long measurements with mobile weather stations (Kestrel 5400) were conducted. The PET considers the energy balance of the human body (e.g. activity, clothing, age) and is therefore explicitly suitable to estimate heat-stress experienced by humans and cooling by trees. Results show that all trees can reduce the PET on average by 10-17 °C for the 5-hour period and that foliage cover was the most limiting factor of the studied tree characteristics. However, trees with sparse foliage cover (~30%) showed a PET reduction of 10-13 °C indicating that there is even a large cooling benefit for recently planted or drought-affected trees.
