Enhanced canopy growth precedes senescence in 2005 and 2010 Amazonian droughts
AuthorsLiu, Yi Y.
van Dijk, Albert I.J.M.
Miralles, Diego G.
Evans, Jason P.
de Jeu, Richard A.M.
Parinussa, Robert M.
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
Environmental Science and Engineering Program
Water Desalination and Reuse Research Center (WDRC)
MetadataShow full item record
AbstractUnprecedented 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.
CitationLiu YY, van Dijk AIJM, Miralles DG, McCabe MF, Evans JP, et al. (2018) Enhanced canopy growth precedes senescence in 2005 and 2010 Amazonian droughts. Remote Sensing of Environment 211: 26–37. Available: http://dx.doi.org/10.1016/j.rse.2018.03.035.
SponsorsYYL is a recipient of Thousand Talents Plan for Young Outstanding Scientists, and acknowledges the financial support from the Nanjing University Information Science and Technology (NUIST) startup grant (2243141701020). DGM acknowledges support from the European Research Council (ERC) under grant agreement 715254 (DRY–2–DRY), and the Belgian Science Policy Office (BELSPO) in the framework of the STEREO III programme projects SAT-EX (SR/00/306) and STR3S (SR/02/329). MFM is supported by the King Abdullah University of Science and Technology. PG acknowledges DOE GoAmazon grant DE-SC0011094. All authors would like to thank Alexei Lyapustin and Yujie Wang for providing the EVI based on MAIAC algorithm (Collection 6). GRACE land data were processed by Sean Swenson, supported by the NASA MEaSUREs Program and available at http://grace.jpl.nasa.gov. The authors declare no conflict of interest.
JournalRemote Sensing of Environment