Abstract Reducing night-time air temperature by irrigating urban greenery can ameliorate heat stress in cities. Past studies often used modelling approaches to investigate the irrigation cooling effect during heatwaves. However, few observational studies have compared the differences in micro-scale irrigation cooling effect between heatwave and non-heatwave conditions. This study examines whether nocturnal irrigation cooling effects intensify during heatwaves, as there have been conflicting results in the literature regarding this issue. During the Australian summer of December 2013 to March 2014, this study was conducted in the Royal Botanic Gardens Victoria’s Melbourne Gardens (mixture of Australian and exotic vegetation) and in the Australian Gardens of its Cranbourne Gardens (specialises in Australian vegetation). We used the excess heat factor (EHF) to identify one severe heatwave (EHF = 34.9) and one extreme heatwave (EHF = 155.6) in our study period. Using meteorological observations, irrigation data and one-way ANOVA, we present the differences in cooling associated with irrigation between different types of landscape in the two gardens. During non-heatwave conditions, there was 0.5 °C – 1 °C of cooling associated with overnight irrigation of 20 – 25 mm. During heatwave conditions, several lawn areas recorded greater cooling (2 °C – 4 °C) associated with irrigation of similar amounts, but this phenomenon was not observed in areas dominated by hard surfaces. The magnitude and timing of the irrigation cooling effects also differed in various garden sites, with residual cooling effects observed lasting for several hours in certain sites following nocturnal irrigation events. Our results suggest that some significant cooling at the micro-scale is apparent from irrigated landscape in Melbourne, which has a temperate oceanic climate with occasional heatwaves. Moreover, the irrigation cooling effect in the Melbourne Gardens intensifies during heatwaves. Our findings could inform landscape succession planning to prepare for a hotter future climate.

中文翻译：

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热浪期间灌溉降温效果会增强吗？墨尔本植物园的案例研究

摘要 通过灌溉城市绿化降低夜间气温可以改善城市热应激。过去的研究经常使用建模方法来研究热浪期间的灌溉冷却效果。然而，很少有观察性研究比较热浪和非热浪条件之间微尺度灌溉冷却效果的差异。本研究调查了夜间灌溉降温效果是否在热浪期间加剧，因为关于这个问题的文献中存在相互矛盾的结果。在 2013 年 12 月至 2014 年 3 月的澳大利亚夏季期间，这项研究在维多利亚皇家植物园的墨尔本花园（澳大利亚和外来植被的混合体）和其 Cranbourne 花园的澳大利亚花园（专门研究澳大利亚植被）中进行。我们使用过热因子 (EHF) 来确定研究期间的一次严重热浪 (EHF = 34.9) 和一次极端热浪 (EHF = 155.6)。使用气象观测、灌溉数据和单向方差分析，我们展示了两个花园中不同类型景观之间与灌溉相关的冷却差异。在非热浪条件下，夜间灌溉 20 – 25 毫米会导致 0.5 °C – 1 °C 的降温。在热浪条件下，几个草坪区域记录了与类似数量灌溉相关的更大的冷却（2°C - 4°C），但在以硬表面为主的区域中没有观察到这种现象。不同园地灌溉降温效应的大小和时间也不同，在夜间灌溉事件后，在某些地点观察到持续数小时的残留冷却效果。我们的研究结果表明，墨尔本的灌溉景观明显出现了微观尺度上的一些显着降温，墨尔本属于温带海洋气候，偶尔会出现热浪。此外，墨尔本花园的灌溉降温效果在热浪期间会加剧。我们的发现可以为景观演替规划提供信息，为未来更热的气候做准备。