Abstract Platanus x acerifolia (London Plane) is a widely planted street tree throughout cities in temperate and Mediterranean climates. Heatwave intensity and frequency is likely to increase in these cities as a combined result of the urban heat island and climate change. High air temperature during heatwaves can lead to canopy leaf loss in vulnerable tree species, such as P. acerifolia. This rapid change in canopy cover may lead to subsequent reductions in ecosystem service benefits, such as shade cooling, human well-being, pollution interception and stormwater interception. This study investigates canopy leaf loss in two streets planted with P. acerifolia trees following a summer heatwave and the impacts upon street micrometeorological conditions and human thermal comfort. The plant area index of P. acerifolia, trees, and the micrometeorological conditions under and away from these trees was measured before and after a >43 °C heatwave in Melbourne, Australia. Physiological equivalent temperature was calculated from micrometeorological parameters to estimate human thermal comfort. Canopy loss was significant (30–50 %) and rapid and reduced thermal comfort benefits provided by canopy shade on two of the three warm summer days measured after the heatwave. However, the under-canopy areas of the street maintained a cooler micrometeorological conditions than areas in the open. This study suggests that as summer air temperature extremes and heatwave frequency increase in urban areas, more vulnerable urban tree species may experience sparse canopy cover throughout summer months reducing some ecosystem service benefits when they are needed most.

中文翻译：

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伦敦梧桐树（Platanus x acerifolia）在热浪之前、期间和之后：失去叶子意味着更少的冷却效益

摘要 Platanus x acerifolia (London Plane) 是一种在温带和地中海气候的城市中广泛种植的行道树。作为城市热岛和气候变化的综合结果，这些城市的热浪强度和频率可能会增加。热浪期间的高气温会导致脆弱树种（如 P. acerifolia）的冠层叶片脱落。冠层覆盖的这种快速变化可能会导致生态系统服务效益的后续减少，例如遮荫降温、人类福祉、污染拦截和雨水拦截。本研究调查了夏季热浪后两条种植 P. acerifolia 树的街道的冠层叶片损失以及对街道微气象条件和人类热舒适度的影响。P. acerifolia, 树木的植物面积指数，在澳大利亚墨尔本 > 43 °C 的热浪之前和之后，测量了这些树木下面和远离这些树木的微气象条件。根据微气象参数计算生理等效温度以估计人体热舒适度。在热浪之后测量的三个温暖夏日中的两个天，树冠遮荫提供了显着的（30-50%）和快速且降低的热舒适益处。然而，街道的树冠下区域比露天区域保持了凉爽的微气象条件。这项研究表明，随着城市地区夏季极端气温和热浪频率的增加，更脆弱的城市树种可能会在整个夏季经历稀疏的树冠覆盖，从而在最需要它们时减少一些生态系统服务的好处。