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Ensemble modelling, uncertainty and robust predictions of organic carbon in long‐term bare‐fallow soils

Roberta Farina 1 Renata Sándor 2, 3 Mohamed Abdalla 4 Jorge Álvaro‐fuentes 5 Luca Bechini 6 Martin Bolinder 7 Lorenzo Brilli 8 Claire Chenu 9 Hugues Clivot 10, 11 Massimiliano de Antoni Migliorati 12 Claudia Di Bene 1 Christopher Dorich 13 Fiona Ehrhardt 14 Fabien Ferchaud 11 Nuala Fitton 4 Rosa Francaviglia 1 Uwe Franko 15 Donna Giltrap 16 Brian Grant 17 Bertrand Guenet 18, 19, 20 Matthew Harrison 21 Miko Kirschbaum 16 Katrin Kuka 22 Liisa Kulmala 23 Jari Liski 23 Matthew Mcgrath 19 Elizabeth Meier 24 Lorenzo Menichetti 7 Fernando Moyano 25 Claas Nendel 26, 27 Sylvie Recous 28 Nils Reibold 25 Anita Shepherd 29, 30 Ward Smith 17 Pete Smith 29 Jean‐françois Soussana 14 Tommaso Stella 31 Arezoo Taghizadeh‐toosi 31 Elena Tsutskikh 32 Gianni Bellocchi 3, 1 
20 MOSAIC - Modélisation des Surfaces et Interfaces Continentales
LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] : DRF/LSCE
Abstract : Simulation models represent soil organic carbon (SOC) dynamics in global carbon (C) cycle scenarios to support climate-change studies. It is imperative to increase confidence in long-term predictions of SOC dynamics by reducing the uncertainty in model estimates. We evaluated SOC simulated from an ensemble of 26 process-based C models by comparing simulations to experimental data from seven long-term bare-fallow (vegetation-free) plots at six sites: Denmark (two sites), France, Russia, Sweden and the United Kingdom. The decay of SOC in these plots has been monitored for decades since the last inputs of plant material, providing the opportunity to test decomposition without the continuous input of new organic material. The models were run independently over multi-year simulation periods (from 28 to 80 years) in a blind test with no calibration (Bln) and with the following three calibration scenarios, each providing different levels of information and/or allowing different levels of model fitting: (a) calibrating decomposition parameters separately at each experimental site (Spe); (b) using a generic, knowledge-based, parameterization applicable in the Central European region (Gen); and (c) using a combination of both (a) and (b) strategies (Mix). We addressed uncertainties from different modelling approaches with or without spin-up initialization of SOC. Changes in the multi-model median (MMM) of SOC were used as descriptors of the ensemble performance. On average across sites, Gen proved adequate in describing changes in SOC, with MMM equal to average SOC (and standard deviation) of 39.2 (+/- 15.5) Mg C/ha compared to the observed mean of 36.0 (+/- 19.7) Mg C/ha (last observed year), indicating sufficiently reliable SOC estimates. Moving to Mix (37.5 +/- 16.7 Mg C/ha) and Spe (36.8 +/- 19.8 Mg C/ha) provided only marginal gains in accuracy, but modellers would need to apply more knowledge and a greater calibration effort than in Gen, thereby limiting the wider applicability of models
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Submitted on : Monday, October 11, 2021 - 3:21:25 PM
Last modification on : Wednesday, September 21, 2022 - 3:24:42 PM
Long-term archiving on: : Wednesday, January 12, 2022 - 8:07:41 PM

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Roberta Farina, Renata Sándor, Mohamed Abdalla, Jorge Álvaro‐fuentes, Luca Bechini, et al.. Ensemble modelling, uncertainty and robust predictions of organic carbon in long‐term bare‐fallow soils. Global Change Biology, Wiley, 2021, 27 (4), pp.904-928. ⟨10.1111/gcb.15441⟩. ⟨hal-03081740⟩

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