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Implementing a new texture-based soil evaporation reduction coefficient in the FAO dual crop coefficient method

Amazirh, Abdelhakim ; Merlin, Olivier ; Er-Raki, Salah ; Bouras, Elhoussaine LU orcid and Chehbouni, Abdelghani (2021) In Agricultural Water Management 250.
Abstract

Crop evapotranspiration (ET) is a fundamental component of the hydrological cycle, especially in arid/semi-arid regions. The FAO-56 offers an operational method for deriving ET from the reduction (dual crop coefficient Kc) of the atmospheric evaporative demand (ET0). The dual coefficient approach (FAO-2Kc) is intended to improve the daily estimation of ET by separating the contribution of bare soil evaporation (E) and crop transpiration components. The FAO-2Kc has been a well-known reference for the operational monitoring of crop water needs. However, its performance for estimating the water use efficiency is limited by uncertainties in the modeled evaporation/transpiration partitioning. This paper aims at... (More)

Crop evapotranspiration (ET) is a fundamental component of the hydrological cycle, especially in arid/semi-arid regions. The FAO-56 offers an operational method for deriving ET from the reduction (dual crop coefficient Kc) of the atmospheric evaporative demand (ET0). The dual coefficient approach (FAO-2Kc) is intended to improve the daily estimation of ET by separating the contribution of bare soil evaporation (E) and crop transpiration components. The FAO-2Kc has been a well-known reference for the operational monitoring of crop water needs. However, its performance for estimating the water use efficiency is limited by uncertainties in the modeled evaporation/transpiration partitioning. This paper aims at improving the soil module of the FAO-2Kc by modifying the E reduction coefficient (Kr) according to soil texture information and state-of-the-art formulations, hence, to amend the mismatch between FAO-2Kc and field-measured data beyond standard conditions. In practice this work evaluates the performance of two evaporation models, using the classical Kr (Kr,FAO) and a new texture-based Kr (Kr,text) over 33 bare soil sites under different evaporative demand and soil conditions. An offline validation is investigated by forcing both models with observed soil moisture (θs) data as input. The Kr,text methodology provides more accurate E estimations compared to the Kr,FAO method and systematically reduces biases. Using Kr,text allows reaching the lowest root means square error (RMSE) of 0.16 mm/day compared to the Kr,FAO where the lowest RMSE reached is 0.88 mm/day. As a step further in the assessment of the proposed methodology, ET was estimated in three wheat fields across the entire agricultural season. Both approaches were thus inter-compared in terms of ET estimates forced by SM estimated as a residual of the water balance model (online validation). Compared to ET measurements, the new formulation provided more accurate results. The RMSE was 0.66 mm/day (0.71 mm/day) and the R2 was 0.83 (0.78) for the texture-based (classical) Kr.

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publishing date
type
Contribution to journal
publication status
published
subject
keywords
Evapotranspiration, FAO-2Kc, Soil evaporation, Soil moisture, Soil texture
in
Agricultural Water Management
volume
250
article number
106827
publisher
Elsevier
external identifiers
  • scopus:85101595518
ISSN
0378-3774
DOI
10.1016/j.agwat.2021.106827
language
English
LU publication?
no
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Funding Information: This study was conducted within the Center of remote sensing application ( https://crsa.um6p.ma/ ), at the Mohammed VI university-Morocco and was funded by the European Commission Horizon 2020 Programme for Research and Innovation , Spain (H2020) in the context of the Marie Sklodowska-Curie Research and Innovation Staff Exchange , Spain (RISE) action ( REC project , Spain grant agreement no: 645642 ), followed by ACCWA project , Spain grant agreement no. 823965 ). The in situ data set was provided by the Joint International Laboratory TREMA ( https://www.lmi-trema.ma/ ), the European Fluxes Database Cluster ( http://www.europe-fluxdata.eu ), the AmeriFlux sites, OzFlux site, long term observatories (AMMA, HOBE and SudMed), and the short term intensive field campaigns (EFEDA, ReSeDa, Yaqui’08, HAPEX-Sahel, IHOP, Monsoon’90 and SGP’97). The French Agence Nationale de la Recherche (MIXMOD-E project, ANR- 13-JS06-0003-01) is also acknowledged for extracting and pre-processing the bare soil evaporation database. PRIMA-IDEWA project is also acknowledged. Finally, the authors are grateful to the editor and two anonymous reviewers for their helpful comments which greatly improved earlier versions of the manuscript. Funding Information: This study was conducted within the Center of remote sensing application (https://crsa.um6p.ma/), at the Mohammed VI university-Morocco and was funded by the European Commission Horizon 2020 Programme for Research and Innovation, Spain (H2020) in the context of the Marie Sklodowska-Curie Research and Innovation Staff Exchange, Spain (RISE) action (REC project, Spain grant agreement no: 645642), followed by ACCWA project, Spain grant agreement no. 823965). The in situ data set was provided by the Joint International Laboratory TREMA (https://www.lmi-trema.ma/), the European Fluxes Database Cluster (http://www.europe-fluxdata.eu), the AmeriFlux sites, OzFlux site, long term observatories (AMMA, HOBE and SudMed), and the short term intensive field campaigns (EFEDA, ReSeDa, Yaqui?08, HAPEX-Sahel, IHOP, Monsoon?90 and SGP?97). The French Agence Nationale de la Recherche (MIXMOD-E project, ANR- 13-JS06-0003-01) is also acknowledged for extracting and pre-processing the bare soil evaporation database. PRIMA-IDEWA project is also acknowledged. Finally, the authors are grateful to the editor and two anonymous reviewers for their helpful comments which greatly improved earlier versions of the manuscript. Publisher Copyright: © 2021 Elsevier B.V.
id
e86c0354-8b71-4bbb-a443-ae2901986b53
date added to LUP
2023-01-04 09:48:58
date last changed
2023-01-20 16:59:40
@article{e86c0354-8b71-4bbb-a443-ae2901986b53,
  abstract     = {{<p>Crop evapotranspiration (ET) is a fundamental component of the hydrological cycle, especially in arid/semi-arid regions. The FAO-56 offers an operational method for deriving ET from the reduction (dual crop coefficient K<sub>c</sub>) of the atmospheric evaporative demand (ET<sub>0</sub>). The dual coefficient approach (FAO-2Kc) is intended to improve the daily estimation of ET by separating the contribution of bare soil evaporation (E) and crop transpiration components. The FAO-2Kc has been a well-known reference for the operational monitoring of crop water needs. However, its performance for estimating the water use efficiency is limited by uncertainties in the modeled evaporation/transpiration partitioning. This paper aims at improving the soil module of the FAO-2Kc by modifying the E reduction coefficient (K<sub>r</sub>) according to soil texture information and state-of-the-art formulations, hence, to amend the mismatch between FAO-2Kc and field-measured data beyond standard conditions. In practice this work evaluates the performance of two evaporation models, using the classical Kr (K<sub>r,FAO</sub>) and a new texture-based Kr (K<sub>r,text</sub>) over 33 bare soil sites under different evaporative demand and soil conditions. An offline validation is investigated by forcing both models with observed soil moisture (θ<sub>s</sub>) data as input. The K<sub>r,text</sub> methodology provides more accurate E estimations compared to the K<sub>r,FAO</sub> method and systematically reduces biases. Using K<sub>r,text</sub> allows reaching the lowest root means square error (RMSE) of 0.16 mm/day compared to the K<sub>r,FAO</sub> where the lowest RMSE reached is 0.88 mm/day. As a step further in the assessment of the proposed methodology, ET was estimated in three wheat fields across the entire agricultural season. Both approaches were thus inter-compared in terms of ET estimates forced by SM estimated as a residual of the water balance model (online validation). Compared to ET measurements, the new formulation provided more accurate results. The RMSE was 0.66 mm/day (0.71 mm/day) and the R<sup>2</sup> was 0.83 (0.78) for the texture-based (classical) Kr.</p>}},
  author       = {{Amazirh, Abdelhakim and Merlin, Olivier and Er-Raki, Salah and Bouras, Elhoussaine and Chehbouni, Abdelghani}},
  issn         = {{0378-3774}},
  keywords     = {{Evapotranspiration; FAO-2Kc; Soil evaporation; Soil moisture; Soil texture}},
  language     = {{eng}},
  month        = {{05}},
  publisher    = {{Elsevier}},
  series       = {{Agricultural Water Management}},
  title        = {{Implementing a new texture-based soil evaporation reduction coefficient in the FAO dual crop coefficient method}},
  url          = {{http://dx.doi.org/10.1016/j.agwat.2021.106827}},
  doi          = {{10.1016/j.agwat.2021.106827}},
  volume       = {{250}},
  year         = {{2021}},
}