Unprecedented droughts hit southern Amazonia in 2005 and 2010, causing a sharp increase in tree mortality and carbon loss. To better predict the rainforest's response to future droughts, it is necessary to understand its behavior during past events. Satellite observations provide a practical source of continuous observations of Amazonian forest. Here we used a passive microwave-based vegetation water content record (i.e., vegetation optical depth, VOD), together with multiple hydrometeorological observations as well as conventional satellite vegetation measures, to investigate the rainforest canopy dynamics during the 2005 and 2010 droughts. During the onset of droughts in the wet-to-dry season (May–July) of both years, we found large-scale positive anomalies in VOD, leaf area index (LAI) and enhanced vegetation index (EVI) over the southern Amazonia. These observations are very likely caused by enhanced canopy growth. Concurrent below-average rainfall and above-average radiation during the wet-to-dry season can be interpreted as an early arrival of normal dry season conditions, leading to enhanced new leaf development and ecosystem photosynthesis, as supported by field observations. Our results suggest that further rainfall deficit into the subsequent dry season caused water and heat stress during the peak of 2005 and 2010 droughts (August–October) that exceeded the tolerance limits of the rainforest, leading to widespread negative VOD anomalies over the southern Amazonia. Significant VOD anomalies were observed mainly over the western part in 2005 and mainly over central and eastern parts in 2010. The total area with significant negative VOD anomalies was comparable between these two drought years, though the average magnitude of significant negative VOD anomalies was greater in 2005. This finding broadly agrees with the field observations indicating that the reduction in biomass carbon uptake was stronger in 2005 than 2010. The enhanced canopy growth preceding drought-induced senescence should be taken into account when interpreting the ecological impacts of Amazonian droughts.

2005年和2010年，史无前例的干旱袭击了南部亚马逊地区，导致树木死亡率和碳损失急剧增加。为了更好地预测雨林对未来干旱的反应，有必要了解其在过去事件中的行为。卫星观测提供了连续观测亚马逊河森林的实用资源。在这里，我们使用了基于微波的被动式植被含水量记录（即，植被光学深度，VOD），以及多种水文气象观测以及常规的卫星植被措施，以调查2005年和2010年干旱期间的雨林冠层动态。在这两年的干湿季（5月至7月）干旱期间，我们发现VOD出现了大规模的正异常，南部亚马逊地区的叶面积指数（LAI）和增强植被指数（EVI）。这些观察结果很可能是由冠层生长增强引起的。湿到干季期间降雨低于平均水平和辐射高于平均水平可以解释为正常干燥季节条件的提前到达，这得到了实地观测的支持，从而增强了新叶片的发育和生态系统的光合作用。我们的结果表明，在随后的干旱季节，进一步的降雨不足导致了2005年和2010年干旱高峰期（8月至10月）的水和热胁迫，其超过了雨林的容忍度，导致南部亚马逊地区普遍出现负VOD异常。重大VOD异常主要发生在2005年的西部地区，主要是在2010年的中部和东部地区。