GMD Geoscientific Model Development GMD Geosci. Model Dev. 1991-9603 Copernicus Publications Göttingen, Germany 10.5194/gmd-7-1115-2014 Testing conceptual and physically based soil hydrology schemes against observations for the Amazon Basin Guimberteau M. https://orcid.org/0000-0001-8582-6087 1 2 Ducharne A. 1 2 3 4 Ciais P. 1 2 5 6 7 Boisier J. P. 1 2 Peng S. https://orcid.org/0000-0001-5098-726X 1 2 5 6 7 8 De Weirdt M. 9 Verbeeck H. https://orcid.org/0000-0003-1490-0168 9 Institut Pierre Simon Laplace (IPSL), Paris, France Centre National de la Recherche Scientifique (CNRS), Paris, France Unité Mixte de Recherche (UMR) METIS 7619, Paris, France Université Pierre et Marie Curie (UPMC), Paris, France Laboratoire des Sciences du Climat et de l'Environment (LSCE), 91191 Gif-sur-Yvette, France Joint Unit of Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Gif-sur-Yvette, France Université de Versailles Saint-Quentin (UVSQ), Versailles, France UJF Grenoble 1, Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE, UMR5183), Grenoble, France Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium 06 06 2014 7 3 1115 1136 Copyright: © 2014 M. Guimberteau et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://gmd.copernicus.org/articles/7/1115/2014/gmd-7-1115-2014.html The full text article is available as a PDF file from https://gmd.copernicus.org/articles/7/1115/2014/gmd-7-1115-2014.pdf

This study analyzes the performance of the two soil hydrology schemes of the land surface model ORCHIDEE in estimating Amazonian hydrology and phenology for five major sub-basins (Xingu, Tapajós, Madeira, Solimões and Negro), during the 29-year period 1980–2008. A simple 2-layer scheme with a bucket topped by an evaporative layer is compared to an 11-layer diffusion scheme. The soil schemes are coupled with a river routing module and a process model of plant physiology, phenology and carbon dynamics. The simulated water budget and vegetation functioning components are compared with several data sets at sub-basin scale. The use of the 11-layer soil diffusion scheme does not significantly change the Amazonian water budget simulation when compared to the 2-layer soil scheme (+3.1 and −3.0% in evapotranspiration and river discharge, respectively). However, the higher water-holding capacity of the soil and the physically based representation of runoff and drainage in the 11-layer soil diffusion scheme result in more dynamic soil water storage variation and improved simulation of the total terrestrial water storage when compared to GRACE satellite estimates. The greater soil water storage within the 11-layer scheme also results in increased dry-season evapotranspiration (+0.5 mm d<sup>−1</sup>, +17%) and improves river discharge simulation in the southeastern sub-basins such as the Xingu. Evapotranspiration over this sub-basin is sustained during the whole dry season with the 11-layer soil diffusion scheme, whereas the 2-layer scheme limits it after only 2 dry months. Lower plant drought stress simulated by the 11-layer soil diffusion scheme leads to better simulation of the seasonal cycle of photosynthesis (GPP) when compared to a GPP data-driven model based on eddy covariance and satellite greenness measurements. A dry-season length between 4 and 7 months over the entire Amazon Basin is found to be critical in distinguishing differences in hydrological feedbacks between the soil and the vegetation cover simulated by the two soil schemes. On average, the multilayer soil diffusion scheme provides little improvement in simulated hydrology over the wet tropical Amazonian sub-basins, but a more significant improvement is found over the drier sub-basins. The use of a multilayer soil diffusion scheme might become critical for assessments of future hydrological changes, especially in southern regions of the Amazon Basin where longer dry seasons and more severe droughts are expected in the next century.

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