Articles | Volume 20, issue 10
Hydrol. Earth Syst. Sci., 20, 4237–4264, 2016
Hydrol. Earth Syst. Sci., 20, 4237–4264, 2016

Research article 19 Oct 2016

Research article | 19 Oct 2016

Canopy-scale biophysical controls of transpiration and evaporation in the Amazon Basin

Kaniska Mallick1, Ivonne Trebs1, Eva Boegh2, Laura Giustarini1, Martin Schlerf1, Darren T. Drewry3,12, Lucien Hoffmann1, Celso von Randow4, Bart Kruijt5, Alessandro Araùjo6, Scott Saleska7, James R. Ehleringer8, Tomas F. Domingues9, Jean Pierre H. B. Ometto4, Antonio D. Nobre4, Osvaldo Luiz Leal de Moraes10, Matthew Hayek11, J. William Munger11, and Steven C. Wofsy11 Kaniska Mallick et al.
  • 1Department of Environmental Research and Innovation, Luxembourg Institute of Science and Technology (LIST), L4422, Belvaux, Luxembourg
  • 2Department of Science and Environment, Roskilde University, Roskilde, Denmark
  • 3Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, 91109, USA
  • 4Instituto Nacional de Pesquisas Espaciais (INPE), Centro de Ciência do Sistema Terrestre, São José dos Campos, SP, Brazil
  • 5Wageningen Environmental Research (ALTERRA), Wageningen, the Netherlands
  • 6Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Belém, PA, Brazil
  • 7Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
  • 8Department of Biology, University of Utah, Salt Lake City, UT, USA
  • 9Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo (USP), São Paulo, SP, Brazil
  • 10Centro Nacional de Monitoramento e Alertas de Desastres Naturais, São Paulo, SP, Brazil
  • 11Department of Earth and Planetary Science, Harvard University, Cambridge, MA, USA
  • 12Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, California, USA

Abstract. Canopy and aerodynamic conductances (gC and gA) are two of the key land surface biophysical variables that control the land surface response of land surface schemes in climate models. Their representation is crucial for predicting transpiration (λET) and evaporation (λEE) flux components of the terrestrial latent heat flux (λE), which has important implications for global climate change and water resource management. By physical integration of radiometric surface temperature (TR) into an integrated framework of the Penman–Monteith and Shuttleworth–Wallace models, we present a novel approach to directly quantify the canopy-scale biophysical controls on λET and λEE over multiple plant functional types (PFTs) in the Amazon Basin. Combining data from six LBA (Large-scale Biosphere-Atmosphere Experiment in Amazonia) eddy covariance tower sites and a TR-driven physically based modeling approach, we identified the canopy-scale feedback-response mechanism between gC, λET, and atmospheric vapor pressure deficit (DA), without using any leaf-scale empirical parameterizations for the modeling. The TR-based model shows minor biophysical control on λET during the wet (rainy) seasons where λET becomes predominantly radiation driven and net radiation (RN) determines 75 to 80 % of the variances of λET. However, biophysical control on λET is dramatically increased during the dry seasons, and particularly the 2005 drought year, explaining 50 to 65 % of the variances of λET, and indicates λET to be substantially soil moisture driven during the rainfall deficit phase. Despite substantial differences in gA between forests and pastures, very similar canopy–atmosphere "coupling" was found in these two biomes due to soil moisture-induced decrease in gC in the pasture. This revealed the pragmatic aspect of the TR-driven model behavior that exhibits a high sensitivity of gC to per unit change in wetness as opposed to gA that is marginally sensitive to surface wetness variability. Our results reveal the occurrence of a significant hysteresis between λET and gC during the dry season for the pasture sites, which is attributed to relatively low soil water availability as compared to the rainforests, likely due to differences in rooting depth between the two systems. Evaporation was significantly influenced by gA for all the PFTs and across all wetness conditions. Our analytical framework logically captures the responses of gC and gA to changes in atmospheric radiation, DA, and surface radiometric temperature, and thus appears to be promising for the improvement of existing land–surface–atmosphere exchange parameterizations across a range of spatial scales.

Short summary
While quantifying vegetation water use over multiple plant function types in the Amazon Basin, we found substantial biophysical control during drought as well as a water-stress period and dominant climatic control during a water surplus period. This work has direct implication in understanding the resilience of the Amazon forest in the spectre of frequent drought menace as well as the role of drought-induced plant biophysical functioning in modulating the water-carbon coupling in this ecosystem.