Comparing observations and process-based simulationsof biosphere-atmosphere exchanges on multiple timescales

E.J. Moors, M.D. Mahecha, M. Reichstein, M. Jung, S.I. Seneviratne, S. Zaehle, C. Beer, M.C. Braakhekke, N. Carvalhais, H. Lange, G. Le Maire

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55 Citations (Scopus)

Abstract

Terrestrial biosphere models are indispensable tools for analyzing the biosphere-atmosphere exchange of carbon and water. Evaluation of these models using site level observations scrutinizes our current understanding of biospheric responses to meteorological variables. Here we propose a novel model-data comparison strategy considering that CO2 and H2O exchanges fluctuate on a wide range of timescales. Decomposing simulated and observed time series into subsignals allows to quantify model performance as a function of frequency, and to localize model-data disagreement in time. This approach is illustrated using site level predictions from two models of different complexity, Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) and Lund-Potsdam-Jena (LPJ), at four eddy covariance towers in different climates. Frequency-dependent errors reveal substantial model-data disagreement in seasonal-annual and high-frequency net CO2 fluxes. By localizing these errors in time we can trace these back, for example, to overestimations of seasonal-annual periodicities of ecosystem respiration during spring greenup and autumn in both models. In the same frequencies, systematic misrepresentations of CO2 uptake severely affect the performance of LPJ, which is a consequence of the parsimonious representation of phenology. ORCHIDEE shows pronounced model-data disagreements in the high-frequency fluctuations of evapotranspiration across the four sites. We highlight the advantages that our novel methodology offers for a rigorous model evaluation compared to classical model evaluation approaches. We propose that ongoing model development will benefit from considering model-data (dis)agreements in the time-frequency domain
Original languageEnglish
Article numberG02003
Number of pages21
JournalJournal of Geophysical Research: Biogeosciences
Volume115
DOIs
Publication statusPublished - 2010

Keywords

  • net ecosystem exchange
  • interannual time scales
  • global vegetation model
  • energy-balance closure
  • eddy covariance
  • stomatal conductance
  • climate-change
  • water-vapor
  • pine forest
  • long-term

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    Moors, E. J., Mahecha, M. D., Reichstein, M., Jung, M., Seneviratne, S. I., Zaehle, S., Beer, C., Braakhekke, M. C., Carvalhais, N., Lange, H., & Le Maire, G. (2010). Comparing observations and process-based simulationsof biosphere-atmosphere exchanges on multiple timescales. Journal of Geophysical Research: Biogeosciences, 115, [G02003]. https://doi.org/10.1029/2009JG001016