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 (CEB,s) 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. CEB,s 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. CEB,s in landscapes with uniform plant functional type approached 0.9 and CEB,s 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.

Stoy, P.; Mauder, M.; Foken, T.; Marcolla, B.; Boegh, E.; Ibrom, A.; Arain, M.A.; Arneth, A.; Aurela, M.; Bernhofer, C.; Cescatti, A.; Dellwik, E.; Duce, P.; Gianelle, D.; van Gorsel, E.; Kiely, G.; Knohl, A.; Margolis, H.; Mccaughey, H.; Merbold, L.; Montagnani, L.; Papale, D.; Reichstein, M.; Serrano Ortiz, P.; Sottocornola, M.; Saunders, M.; Spano, D.; Vaccari, F.; Varlagin, A. (2013). A data-driven analysis of energy balance closure across FLUXNET research sites: the role of landscape-scale heterogeneity. AGRICULTURAL AND FOREST METEOROLOGY, 171-172: 137-152. doi: 10.1016/j.agrformet.2012.11.004 handle: http://hdl.handle.net/10449/21914

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

Marcolla, Barbara;Gianelle, Damiano;Sottocornola, Matteo;
2013-01-01

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 (CEB,s) 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. CEB,s 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. CEB,s in landscapes with uniform plant functional type approached 0.9 and CEB,s 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.
Eddy covariance
Energy balance closure
Enhanced vegetation index
FLUXNET
MODIS
Plant functional type
Settore BIO/07 - ECOLOGIA
2013
Stoy, P.; Mauder, M.; Foken, T.; Marcolla, B.; Boegh, E.; Ibrom, A.; Arain, M.A.; Arneth, A.; Aurela, M.; Bernhofer, C.; Cescatti, A.; Dellwik, E.; Duce, P.; Gianelle, D.; van Gorsel, E.; Kiely, G.; Knohl, A.; Margolis, H.; Mccaughey, H.; Merbold, L.; Montagnani, L.; Papale, D.; Reichstein, M.; Serrano Ortiz, P.; Sottocornola, M.; Saunders, M.; Spano, D.; Vaccari, F.; Varlagin, A. (2013). A data-driven analysis of energy balance closure across FLUXNET research sites: the role of landscape-scale heterogeneity. AGRICULTURAL AND FOREST METEOROLOGY, 171-172: 137-152. doi: 10.1016/j.agrformet.2012.11.004 handle: http://hdl.handle.net/10449/21914
File in questo prodotto:
File Dimensione Formato  
2013 AFM Stoy et al.pdf

solo utenti autorizzati

Licenza: Tutti i diritti riservati (All rights reserved)
Dimensione 1.88 MB
Formato Adobe PDF
1.88 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10449/21914
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 418
  • ???jsp.display-item.citation.isi??? 409
social impact