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

Stoy, Paul C.; Mauder, Matthias; Foken, Thomas; Marcolla, Barbara; Boegh, Eva; Ibrom, Andreas; Arain, M. Altaf; Arneth, Almut LU ; Aurela, Mika and Bernhofer, Christian, et al. (2013) In Agricultural and Forest Meteorology 171. p.137-152
Abstract
The energy balance at most surface-atmosphere flux research sites remains unclosed. The mechanisms underlying the discrepancy between measured energy inputs and outputs across the global FLUXNET tower network are still under debate. 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 some intensively-researched sites, while unmeasured storage terms cannot be ruled out as a dominant contributor to the lack of energy balance closure at many other sites. We analyzed energy balance closure across 173 ecosystems in the FLUXNET database and explored the relationship between energy balance closure and... (More)
The energy balance at most surface-atmosphere flux research sites remains unclosed. The mechanisms underlying the discrepancy between measured energy inputs and outputs across the global FLUXNET tower network are still under debate. 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 some intensively-researched sites, while unmeasured storage terms cannot be ruled out as a dominant contributor to the lack of energy balance closure at many other sites. We analyzed energy balance closure across 173 ecosystems in the FLUXNET database and explored the relationship between energy balance closure and landscape heterogeneity using MODIS products and GLOBEstat elevation data. Energy balance closure per research site (C-EBS)averaged 0.84 +/- 0.20, with best average closures in evergreen broadleaf forests and savannas (0.91-0.94) and worst average closures in crops, deciduous broadleaf forests, mixed forests and wetlands (0.70-0.78). Half-hourly or hourly energy balance closure on a percent basis increased with friction velocity (u.) and was highest on average under near-neutral atmospheric conditions. C-EBS was significantly related to mean precipitation, gross primary productivity and landscape-level enhanced vegetation index (EVI) from MODIS, and the 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. C-EBS in landscapes with uniform plant functional type approached 0.9 and C-EBS in landscapes with uniform EVI approached 1. These results suggest that landscape-level heterogeneity in vegetation and topography cannot be ignored as a contributor to incomplete energy balance closure at the flux network level, although net radiation measurements, biological energy assimilation, unmeasured storage terms, and the importance of good practice including site selection when making flux measurements should not be discounted. Our results suggest that future research should focus on the quantitative mechanistic relationships between energy balance closure and landscape-scale heterogeneity, and the consequences of mesoscale circulations for surface-atmosphere exchange measurements. (C) 2012 Elsevier B.V. All rights reserved. (Less)
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keywords
Eddy covariance, Energy balance closure, Enhanced vegetation index
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Agricultural and Forest Meteorology
volume
171
pages
137 - 152
publisher
Elsevier
external identifiers
  • wos:000316513000014
  • scopus:84874241558
ISSN
1873-2240
DOI
10.1016/j.agrformet.2012.11.004
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English
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ae01471e-2732-4dc7-99c9-a881d9baafed (old id 3635981)
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2013-04-24 12:33:46
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@article{ae01471e-2732-4dc7-99c9-a881d9baafed,
  abstract     = {The energy balance at most surface-atmosphere flux research sites remains unclosed. The mechanisms underlying the discrepancy between measured energy inputs and outputs across the global FLUXNET tower network are still under debate. 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 some intensively-researched sites, while unmeasured storage terms cannot be ruled out as a dominant contributor to the lack of energy balance closure at many other sites. We analyzed energy balance closure across 173 ecosystems in the FLUXNET database and explored the relationship between energy balance closure and landscape heterogeneity using MODIS products and GLOBEstat elevation data. Energy balance closure per research site (C-EBS)averaged 0.84 +/- 0.20, with best average closures in evergreen broadleaf forests and savannas (0.91-0.94) and worst average closures in crops, deciduous broadleaf forests, mixed forests and wetlands (0.70-0.78). Half-hourly or hourly energy balance closure on a percent basis increased with friction velocity (u.) and was highest on average under near-neutral atmospheric conditions. C-EBS was significantly related to mean precipitation, gross primary productivity and landscape-level enhanced vegetation index (EVI) from MODIS, and the 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. C-EBS in landscapes with uniform plant functional type approached 0.9 and C-EBS in landscapes with uniform EVI approached 1. These results suggest that landscape-level heterogeneity in vegetation and topography cannot be ignored as a contributor to incomplete energy balance closure at the flux network level, although net radiation measurements, biological energy assimilation, unmeasured storage terms, and the importance of good practice including site selection when making flux measurements should not be discounted. Our results suggest that future research should focus on the quantitative mechanistic relationships between energy balance closure and landscape-scale heterogeneity, and the consequences of mesoscale circulations for surface-atmosphere exchange measurements. (C) 2012 Elsevier B.V. All rights reserved.},
  author       = {Stoy, Paul C. and Mauder, Matthias and Foken, Thomas and Marcolla, Barbara and Boegh, Eva and Ibrom, Andreas and Arain, M. Altaf and Arneth, Almut and Aurela, Mika and Bernhofer, Christian and Cescatti, Alessandro and Dellwik, Ebba and Duce, Pierpaolo and Gianelle, Damiano and van Gorsel, Eva and Kiely, Gerard and Knohl, Alexander and Margolis, Hank and McCaughey, Harry and Merbold, Lutz and Montagnani, Leonardo and Papale, Dario and Reichstein, Markus and Saunders, Matthew and Serrano-Ortiz, Penelope and Sottocornola, Matteo and Spano, Donatella and Vaccari, Francesco and Varlagin, Andrej},
  issn         = {1873-2240},
  keyword      = {Eddy covariance,Energy balance closure,Enhanced vegetation index},
  language     = {eng},
  pages        = {137--152},
  publisher    = {Elsevier},
  series       = {Agricultural and Forest Meteorology},
  title        = {A data-driven analysis of energy balance closure across FLUXNET research sites: The role of landscape scale heterogeneity},
  url          = {http://dx.doi.org/10.1016/j.agrformet.2012.11.004},
  volume       = {171},
  year         = {2013},
}