H31A-1405
Stomatal and Aerodynamic Controls of Transpiration and Evaporation over Amazonian Landscapes

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Ivonne Trebs1, Kaniska Mallick1, Eva Boegh2, Laura Giustarini1, Martin Schlerf1, Celso von Randow3, Bart Kruijt4, Alessandro C De Araujo5, Matthew Hayek6, Steven C Wofsy6, J William Munger6, Scott R Saleska7, James R Ehleringer8, Tomas Ferreira Domingues9, Jean Pierre H. B. Ometto10, Osvaldo Luiz Leal de Moraes11, Lucien Hoffmann1 and Andrew Jarvis12, (1)Luxembourg Institute of Science and Technology (LIST), Environmental Research and Innovation, Belvaux, Luxembourg, (2)Roskilde University, Roskilde, Denmark, (3)Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brazil, (4)Alterra, Wageningen, Netherlands, (5)Brazilian Agricultural Research Corporation (EMBRAPA), Belem, PA, Brazil, (6)Harvard University, Cambridge, MA, United States, (7)University of Arizona, Tucson, AZ, United States, (8)Univ Utah, Salt Lake City, UT, United States, (9)USP University of Sao Paulo, São Paulo, Brazil, (10)Instituto Nacional de Pesquisas Espaciais (INPE), Centro de Ciência do Sistema Terrestre, São José dos Campos, Brazil, (11)Centro Nacional de Monitoramento e Alertas de Desastres Naturais, Cachoeira Paulista, Brazil, (12)Lancaster University, Lancaster Environment Centre, Lancaster, United Kingdom
Abstract:
The dominant physical and ecophysiological state variables regulating the terrestrial latent heat flux (λE) are the aerodynamic conductance exerted by the boundary layer (gB) and the stomatal conductance (gS) exerted by the vegetation, and the Penman-Monteith (PM) model is a physically based method to directly quantify λE. However, the large scale application of the PM model suffers from the unavailability of any physical approach that explains the behaviour of gB and gSwithin the soil-plant-atmosphere-continuum.

Here, we present a novel method to directly estimate gB and gS, and quantify their control on canopy scale transpiration (λET) and evaporation (λEE) using a Surface Temperature Initiated Closure (STIC) approach. STIC is driven with radiometric surface temperature (TR), air temperature (TA), relative humidity (RH), net radiation (RN), and ground heat flux (G). It physically integrates TR into the PM formulation to directly retrieve gB and gS and the conductances are physically constrained by near surface wetness, atmospheric vapour pressure deficit (DA) and radiative fluxes. Measurements from six ecohydrologically contrasting sites of the LBA (Large Scale Biosphere Atmosphere Transfer in Amazonia) eddy covariance network were used for estimating the conductances and quantifying their control on λET and λEE.

The predicted λE from STIC based gB and gS retrievals revealed substantial correlation (R2 from 0.92 to 0.98), and mean absolute percent deviation (MAPD) of 14% to 20% with the observed fluxes. The ‘decoupling coefficient’ (Ω) indicated critical canopy control on λET and λEE for Tropical Moist Forest (TMF), Tropical Dry Forest (TDF) and pasture (PAS). On the contrary, for the Tropical Rain Forest (TRF) site, a non-significant relationship was found between Ω and λET (λEE) (p = 0.20 – 0.42), indicating no canopy control on λET (λEE) for this particular plant functional type. However, significant canopy control for the TRF was found in the drought year of 2005. Equilibrium transpiration dominated in TRF, with RN mainly controlling λET, whereas a significant proportion of λET was imposed due to substantial canopy-atmosphere coupling in the dry sites. These findings may have significant implications for ecohydrological interactions under land use change in the Amazon Basin.

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