A data-driven analysis of energy balance closure across FLUXNET research sites: The role of landscape scale heterogeneity

Despite excellent energy balance closure at some eddy covariance research sites, the energy balance at most sites remains unclosed. Mechanisms for the lack of closure across the global FLUXNET tower network remain unclear. Recent reviews have identified exchange processes and turbulent motions at large spatial and temporal scales in heterogeneous landscapes as the primary cause of the lack of energy balance closure at select, intensively-researched sites. We characterized energy balance closure across 180 ecosystems in the FLUXNET database, including relationships with landscape heterogeneity using MODIS products and GLOBEstat elevation data. Energy balance closure per research site (CEB,s) averaged 0.83 ± 0.25, with best average closure in evergreen broadleaf forests and savannas (0.91-0.94) and worst average closure in crops, mixed forests and wetlands (0.70-0.78). Instantaneous energy balance closure increased with friction velocity (u*), especially over the lower u*range, decreased with solar zenith angle, and was greatest for near-neutral atmospheric conditions. CEB,s was significantly related to mean precipitation, gross primary productivity and landscape-level enhanced vegetation index (EVI) from MODIS. CEB,s was also significantly related to landscape-level variability in elevation, MODIS plant functional type, and MODIS EVI. A linear model including landscape-level variability in both EVI and elevation, mean precipitation, and an interaction term between EVI variability and precipitation had the lowest Akaike’s Information Criterion value. CEB,s in landscapes with uniform plant functional type approached 0.9 and CEB,s in landscapes with uniform EVI approached 1. These results point to the role of landscape-level heterogeneity in vegetation and topography as a likely explanation for incomplete energy balance closure at the network level, although metabolism, unmeasured storage terms, and the importance of good practice when making flux measurements should not be discounted. Future research should focus on physical explanations for the relationship between energy balance closure and landscape heterogeneity.

STOY P.;  MAUDER M.;  FOKEN Thomas;  MARCOLLA B.;  BOEGH Eva;  IBROM A;  ARAIN Altaf;  ARNETH Almut;  AURELA Mika;  BERNHOFER Christian;  CESCATTI Alessandro;  GIANELLE Damiano;  VAN GORSEL Eva;  KIELY Gerald;  KNOHL Alexander;  MARGOLIS Hank;  MONTAGNANI Leonardo;  PAPALE Dario;  REICHSTEIN M.;  SOTTOCORNOLA Matteo;  VACCARI Francesco;  VARLAGIN Andrej;  DUCE Pierpaolo;  MCCAUGHEY Harry;  DELLWIK E.;  MERBOLD Lutz;  SAUNDERS Matthew;  SERRANO-ORTIZ Penelope;  SPANO Donatella; 

2014-03-03

ELSEVIER SCIENCE BV

JRC79116

0168-1923,   

http://www.sciencedirect.com/science/article/pii/S0168192312003413,    https://publications.jrc.ec.europa.eu/repository/handle/JRC79116,   

10.1016/j.agrformet.2012.11.004,