Department of Earth System Science, Tsinghua University, Beijing 100084, China.
Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095;
Proc Natl Acad Sci U S A. 2017 Aug 8;114(32):8481-8486. doi: 10.1073/pnas.1621516114. Epub 2017 Jul 20.
Although it is well established that transpiration contributes much of the water for rainfall over Amazonia, it remains unclear whether transpiration helps to drive or merely responds to the seasonal cycle of rainfall. Here, we use multiple independent satellite datasets to show that rainforest transpiration enables an increase of shallow convection that moistens and destabilizes the atmosphere during the initial stages of the dry-to-wet season transition. This shallow convection moisture pump (SCMP) preconditions the atmosphere at the regional scale for a rapid increase in rain-bearing deep convection, which in turn drives moisture convergence and wet season onset 2-3 mo before the arrival of the Intertropical Convergence Zone (ITCZ). Aerosols produced by late dry season biomass burning may alter the efficiency of the SCMP. Our results highlight the mechanisms by which interactions among land surface processes, atmospheric convection, and biomass burning may alter the timing of wet season onset and provide a mechanistic framework for understanding how deforestation extends the dry season and enhances regional vulnerability to drought.
尽管蒸腾作用为亚马逊地区的降雨贡献了大量水分，这一点已得到充分证实，但仍不清楚蒸腾作用是有助于驱动降雨的季节性循环，还是仅仅对此做出响应。在这里，我们使用多个独立的卫星数据集表明，雨林蒸腾作用使浅层对流增加，在干湿季转换的初始阶段使大气加湿和不稳定。这种浅层对流水汽泵（SCMP）使大气在区域尺度上为携带大量水汽的深层对流的快速增加做好准备，这反过来又驱动水汽辐合和雨季的开始，比热带辐合带（ITCZ）的到来提前 2-3 个月。晚干季生物质燃烧产生的气溶胶可能会改变 SCMP 的效率。我们的研究结果强调了陆地表面过程、大气对流和生物质燃烧之间的相互作用改变雨季开始时间的机制，并为理解森林砍伐如何延长旱季以及增强区域对干旱的脆弱性提供了一个机械框架。
