Abstract Heatwave is a serious threat to society and can lead to grave consequences. Although it is well known that persistent large-scale circulation anomalies are the key to generate heatwaves, land-atmosphere interactions have also been suggested to intensify and propagate heatwaves. Vegetation plays a vital role in land-atmosphere interactions, modulating energy and water exchange through various pathways. However, vegetation impacts on surface energy exchange during extreme events such as heatwaves, and the attribution of effects to different vegetation types, is complex and poorly understood. In this study, we found strong interannual correlations between summer heatwaves and various plant function types (PFTs), based on the Global Heatwave and Warm-spell Record (GHWR) and leaf area index (LAI) products from satellites during 1982–2011. In Central Europe and the southern and southeastern part of North America, where the land cover is dominated by grasslands, temperate deciduous forests or temperate needleleaf forests, heatwaves tend to occur more frequently in years with lower LAI. In contrast, in the northwestern and northeastern part of North America, where boreal evergreen forests dominate, higher-than-normal LAI is associated with an increase in heatwave occurrence. These findings are in general supported by composite analyses of extreme LAI years in these PFT regions and heatwave characteristics therein. We speculate that the different surface heat flux responses over different PFTs during heatwaves may explain the above relationships. Focusing on North America, and using various datasets including those generated by the Global Land Data Assimilation System (GLDAS) with three different land surface models (CLM, MOS, NOAH), three reanalysis datasets (MERRA-2, NOAA-CIRES-DOS, NCEP/NCAR), and also observations from an extensive network of flux towers, we found that when temperate and boreal evergreen forests are greener, positive sensible heat anomalies increase significantly during heatwaves. Meanwhile, over boreal evergreen forests, changes in latent heat anomalies are much smaller than the positive sensible heat anomalies, suggesting that a greener boreal evergreen forest may prolong and amplify heatwaves significantly. This generates a positive feedback mechanism that begins with higher LAI in generally warmer years in these temperature-limited regions, thus sustaining the strong positive heatwave-LAI correlation. In contrast, for temperate needleleaf forests, temperate deciduous forests and grasslands, strong positive latent heat anomalies with cloud, precipitation and evaporative cooling feedback during high-LAI years appear to suppress heatwaves regionally. Our study revealed the interannual relationships between heatwaves and vegetation as well as the underlying energy exchange processes for different vegetation types and background climate conditions, with implications for the management of forest resources in view of worsening heatwave severity under the future climate.

中文翻译：

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1982-2011 年北半球不同植被类型对夏季热浪的植被-热浪相关性和能量交换反应对比

摘要 热浪对社会构成严重威胁，并可能导致严重后果。尽管众所周知，持续的大尺度环流异常是产生热浪的关键，但也有人提出陆地-大气相互作用会加剧和传播热浪。植被在陆地-大气相互作用中起着至关重要的作用，通过各种途径调节能量和水的交换。然而，在极端事件（如热浪）期间植被对地表能量交换的影响，以及对不同植被类型的影响归因是复杂的，并且知之甚少。在这项研究中，我们根据 1982-2011 年卫星的全球热浪和暖期记录 (GHWR) 和叶面积指数 (LAI) 产品，发现夏季热浪与各种植物功能类型 (PFT) 之间存在很强的年际相关性。在中欧和北美南部和东南部，土地覆盖以草原、温带落叶林或温带针叶林为主，热浪往往在 LAI 较低的年份更频繁地发生。相比之下，在北美洲的西北部和东北部，北方常绿森林占主导地位，高于正常水平的 LAI 与热浪发生的增加有关。这些发现通常得到对这些 PFT 地区极端 LAI 年和其中的热浪特征的综合分析的支持。我们推测热浪期间不同 PFT 的不同表面热通量响应可以解释上述关系。专注于北美，并使用各种数据集，包括由全球土地数据同化系统 (GLDAS) 生成的数据集和三个不同的地表模型（CLM、MOS、NOAH）、三个再分析数据集（MERRA-2、NOAA-CIRES-DOS、NCEP/NCAR），以及来自广泛的通量塔网络的观察结果，我们发现当温带和北方常绿森林更绿时，热浪期间正感热异常显着增加。同时，在北方常绿林上，潜热异常的变化远小于正感热异常，表明更绿的北方常绿林可能会显着延长和放大热浪。这产生了一种正反馈机制，在这些温度有限的地区，在普遍较暖的年份以较高的 LAI 开始，从而维持强烈的热浪-LAI 正相关。相比之下，对于温带针叶林、温带落叶林和草原，在高 LAI 年，强烈的正潜热异常与云、降水和蒸发冷却反馈似乎在区域上抑制了热浪。我们的研究揭示了热浪与植被之间的年际关系，以及不同植被类型和背景气候条件下潜在的能量交换过程，鉴于未来气候下热浪严重程度不断恶化，这对森林资源的管理产生了影响。高 LAI 年的降水和蒸发冷却反馈似乎抑制了区域性热浪。我们的研究揭示了热浪与植被之间的年际关系，以及不同植被类型和背景气候条件下潜在的能量交换过程，鉴于未来气候下热浪严重程度不断恶化，这对森林资源的管理产生了影响。高 LAI 年的降水和蒸发冷却反馈似乎抑制了区域性热浪。我们的研究揭示了热浪与植被之间的年际关系，以及不同植被类型和背景气候条件下潜在的能量交换过程，鉴于未来气候下热浪严重程度不断恶化，这对森林资源的管理产生了影响。