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

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.

Bibliographic Details

Main Authors:	Mahecha, Miguel D., Reichstein, Markus, Jung, Martin, Seneviratne, Sonia I., Zaehle, Sönke, Beer, Christian, Braakhekke, M.C., Carvalhais, Nuno, Lange, Holger, Le Maire, Guerric, Moors, Eddy J.
Format:	article biblioteca
Language:	eng
Subjects:	U10 - Informatique, mathématiques et statistiques, P40 - Météorologie et climatologie, 000 - Autres thèmes, P01 - Conservation de la nature et ressources foncières, écologie, eau, modélisation environnementale, cycle du carbone, dioxyde de carbone, cycle hydrologique, évapotranspiration, écosystème, modèle de simulation, atmosphère, météorologie, climatologie, http://aims.fao.org/aos/agrovoc/c_2467, http://aims.fao.org/aos/agrovoc/c_8309, http://aims.fao.org/aos/agrovoc/c_9000056, http://aims.fao.org/aos/agrovoc/c_17299, http://aims.fao.org/aos/agrovoc/c_1302, http://aims.fao.org/aos/agrovoc/c_11670, http://aims.fao.org/aos/agrovoc/c_2741, http://aims.fao.org/aos/agrovoc/c_2482, http://aims.fao.org/aos/agrovoc/c_24242, http://aims.fao.org/aos/agrovoc/c_8994, http://aims.fao.org/aos/agrovoc/c_4783, http://aims.fao.org/aos/agrovoc/c_1671,
Online Access:	http://agritrop.cirad.fr/557773/ http://agritrop.cirad.fr/557773/1/document_557773.pdf
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