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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/hess-2020-523
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2020-523
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Nov 2020

14 Nov 2020

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This preprint is currently under review for the journal HESS.

Evapotranspiration in the Amazon: spatial patterns, seasonality and recent trends in observations, reanalysis and CMIP models

Jessica C. A. Baker1, Luis Garcia-Carreras2, Manuel Gloor3, John H. Marsham1,4, Wolfgang Buermann5, Humberto R. da Rocha6, Antonio D. Nobre7, Alessandro Carioca de Araujo8, and Dominick V. Spracklen1 Jessica C. A. Baker et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, UK
  • 2School of Earth and Environmental Sciences, University of Manchester, UK
  • 3School of Geography, University of Leeds, Leeds, UK
  • 4National Centre for Atmospheric Science, Leeds, UK
  • 5Institut fuer Geographie, Universitaet Augsburg, D-86135 Augsburg, Germany
  • 6Departamento de Ciências Atmosféricas, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brasil
  • 7Earth System Science Center, INPE, Av dos Astronautas, 1758, São José dos Campos, SP Brasil
  • 8Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Belém-PA, CEP 66095-100, Brasil

Abstract. Water recycled through transpiring forests influences the spatial distribution of precipitation in the Amazon and has been shown to play a role in the initiation of the wet season. However, due to the challenges and costs associated with measuring evapotranspiration (ET) directly, plus the high uncertainty and discrepancies across remote-sensing retrievals of ET, spatial and temporal patterns in this key component of the Amazon hydrological cycle remain poorly understood. In this study, we estimated ET over the Amazon and ten sub-basins using a catchment-balance approach, whereby ET is calculated directly as the balance between precipitation, runoff and change in groundwater storage. We compared our results with ET from remote-sensing datasets, reanalysis, models from the fifth and sixth Coupled Model Intercomparison Projects (CMIP5 and CMIP6), and in-situ flux-tower measurements, to provide a comprehensive overview of current understanding. Catchment-balance analysis revealed a gradient in ET from east to west/southwest across the Amazon basin, a strong seasonal cycle in basin-mean ET controlled by net incoming radiation, and no trend in ET over the past two decades. Satellite datasets, reanalysis and climate models all tended to overestimate the magnitude of ET relative to catchment-balance estimates, underestimate seasonal and interannual variability, and show conflicting positive and negative trends. Only two out of six satellite and model datasets analysed reproduced spatial and seasonal variation in Amazon ET, and captured the same controls on ET as indicated by catchment-balance analysis. CMIP5 and CMIP6 ET was inconsistent with catchment-balance estimates over all scales analysed. Overall, the discrepancies between data products and models revealed by our analysis demonstrate a need for more ground-based ET measurements in the Amazon, and to substantially improve model representation of this fundamental component of the Amazon hydrological cycle.

Jessica C. A. Baker et al.

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Catchment-scale estimates of Amazon evapotranspiration Jessica C. A. Baker https://doi.org/10.5281/zenodo.4271331

Jessica C. A. Baker et al.

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Short summary
Evapotranspiration (ET) is a vital part of the Amazon water cycle, but is difficult to measure over large areas. In this study, we compare spatial patterns, seasonality and recent trends in Amazon ET from a water-budget analysis with estimates from satellites, reanalysis and global climate models. We find large differences between products, showing that many widely-used datasets and climate models may not provide a reliable representation of this crucial variable over the Amazon.
Evapotranspiration (ET) is a vital part of the Amazon water cycle, but is difficult to measure...
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