Atmospheric vapor pressure deficit (VPD) is a critical variable related to water flux that may either promote or limit plant evapotranspiration under different conditions, consequentially, influencing the effect of urban vegetation on mitigating urban heat island. However, how VPD influence the cooling effect of urban vegetation in different climate zones, have not been examined to date. Here, we combined field observations of 3634 samples from the global published literature and satellite data to investigate the spatial-temporal impacts of VPD on vegetation cooling and reveal the pathways of “atmospheric dryness-evapotranspiration-climate effect”. Our results showed that the cooling effect was generally remarkable in urban areas in the humid season of the tropical/subtropical zones and in the warm season of temperate zones. In the tropical/subtropical zones, the cooling effect was enhanced with increasing VPD across the range of low VPD, but was obviously constrained by high atmospheric dryness when VPD exceeded 9.43 hPa. In contrast, the cooling effects of urban vegetation were gradually strengthened as VPD increased in temperate zones. Notably, tropical and subtropical urban vegetation began to exert a great cooling effect when evapotranspiration per unit leaf area was >31.93 mm/month. Our findings suggest that stronger constraints of atmospheric dryness on cooling effect in the tropical/subtropical zones versus the temperate zone. These findings provide important insights for understanding the patterns of urban vegetation response to atmospheric dryness. They can also assist managers and decision-makers in optimizing the design of urban green space in different geographic locations.

中文翻译：

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大气干燥度对温带和热带/亚热带城市植物降温效果的差异化影响

大气蒸气压赤字（VPD）是与水通量相关的一个关键变量，它可能在不同条件下促进或限制植物蒸散量，从而影响城市植被缓解城市热岛的效果。然而，VPD如何影响不同气候带城市植被的降温效果，迄今为止尚未得到研究。在此，我们结合全球已发表文献中的3634个样本的实地观测和卫星数据，研究VPD对植被降温的时空影响，揭示“大气干燥-蒸散-气候效应”的路径。研究结果表明，热带/亚热带湿润季和温带暖季城市地区降温效果普遍显着。在热带/亚热带地区，在低VPD范围内，降温效果随着VPD的增加而增强，但当VPD超过9.43 hPa时，降温效果明显受到高大气干燥度的制约。相比之下，温带地区随着VPD的增加，城市植被的降温作用逐渐增强。值得注意的是，热带、亚热带城市植被在单位叶面积蒸散量>31.93毫米/月时开始发挥较大的降温作用。我们的研究结果表明，与温带地区相比，热带/亚热带地区的大气干燥度对降温效果的限制更强。这些发现为理解城市植被对大气干燥的响应模式提供了重要的见解。他们还可以协助管理者和决策者优化不同地理位置的城市绿地设计。