Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964;
Earth Institute, Columbia University, New York, NY 10027.
Proc Natl Acad Sci U S A. 2019 Sep 17;116(38):18848-18853. doi: 10.1073/pnas.1904955116. Epub 2019 Sep 3.
Compound extremes such as cooccurring soil drought (low soil moisture) and atmospheric aridity (high vapor pressure deficit) can be disastrous for natural and societal systems. Soil drought and atmospheric aridity are 2 main physiological stressors driving widespread vegetation mortality and reduced terrestrial carbon uptake. Here, we empirically demonstrate that strong negative coupling between soil moisture and vapor pressure deficit occurs globally, indicating high probability of cooccurring soil drought and atmospheric aridity. Using the Global Land Atmosphere Coupling Experiment (GLACE)-CMIP5 experiment, we further show that concurrent soil drought and atmospheric aridity are greatly exacerbated by land-atmosphere feedbacks. The feedback of soil drought on the atmosphere is largely responsible for enabling atmospheric aridity extremes. In addition, the soil moisture-precipitation feedback acts to amplify precipitation and soil moisture deficits in most regions. CMIP5 models further show that the frequency of concurrent soil drought and atmospheric aridity enhanced by land-atmosphere feedbacks is projected to increase in the 21st century. Importantly, land-atmosphere feedbacks will greatly increase the intensity of both soil drought and atmospheric aridity beyond that expected from changes in mean climate alone.
复合极端情况，如土壤干旱（土壤水分低）和大气干旱（高水汽压亏缺），可能对自然和社会系统造成灾难性影响。土壤干旱和大气干旱是导致广泛植被死亡和陆地碳吸收减少的 2 个主要生理胁迫因素。在这里，我们通过实证证明，全球范围内土壤湿度和水汽压亏缺之间存在强烈的负耦合，这表明土壤干旱和大气干旱同时发生的可能性很高。利用全球陆地大气耦合实验（GLACE）-CMIP5 实验，我们进一步表明，土地-大气反馈大大加剧了同时发生的土壤干旱和大气干旱。土壤干旱对大气的反馈在很大程度上导致了大气干旱极端事件的发生。此外，土壤湿度-降水反馈作用在大多数地区放大了降水和土壤湿度的亏缺。CMIP5 模型进一步表明，到 21 世纪，土地-大气反馈增强的同时发生的土壤干旱和大气干旱的频率预计将会增加。重要的是，土地-大气反馈将大大增加土壤干旱和大气干旱的强度，超出仅由平均气候变化所预期的强度。
