Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, USA.
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA.
Sci Rep. 2019 Oct 25;9(1):15331. doi: 10.1038/s41598-019-51857-8.
We show a recent increasing trend in Vapor Pressure Deficit (VPD) over tropical South America in dry months with values well beyond the range of trends due to natural variability of the climate system defined in both the undisturbed Preindustrial climate and the climate over 850-1850 perturbed with natural external forcing. This trend is systematic in the southeast Amazon but driven by episodic droughts (2005, 2010, 2015) in the northwest, with the highest recoded VPD since 1979 for the 2015 drought. The univariant detection analysis shows that the observed increase in VPD cannot be explained by greenhouse-gas-induced (GHG) radiative warming alone. The bivariate attribution analysis demonstrates that forcing by elevated GHG levels and biomass burning aerosols are attributed as key causes for the observed VPD increase. We further show that There is a negative trend in evaporative fraction in the southeast Amazon, where lack of atmospheric moisture, reduced precipitation together with higher incoming solar radiation (~7% decade cloud-cover reduction) influences the partitioning of surface energy fluxes towards less evapotranspiration. The VPD increase combined with the decrease in evaporative fraction are the first indications of positive climate feedback mechanisms, which we show that will continue and intensify in the course of unfolding anthropogenic climate change.
我们展示了南美洲热带地区在干燥月份的蒸气压亏缺（VPD）的近期上升趋势，其值远远超出了气候系统自然变率所定义的未受干扰的前工业化气候和 850-1850 年受自然外部强迫影响的气候的趋势范围。这一趋势在东南亚马逊地区是系统性的，但西北地区则受到偶发性干旱（2005 年、2010 年、2015 年）的驱动，2015 年干旱时期创下了自 1979 年以来有记录以来的最高 VPD。单变量检测分析表明，观测到的 VPD 增加不能仅用温室气体引起的（GHG）辐射变暖来解释。双变量归因分析表明，升高的 GHG 水平和生物质燃烧气溶胶的强迫作用是导致观测到的 VPD 增加的关键原因。我们进一步表明，东南亚马逊地区的蒸发分数呈负趋势，大气湿度不足、降水减少以及更高的入射太阳辐射（~7%的云量减少）影响了地表能量通量向更少的蒸散分配。VPD 的增加加上蒸发分数的减少是积极的气候反馈机制的第一个迹象，我们表明，随着人为气候变化的展开，这些机制将继续并加剧。
