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Geosci. Instrum. Method. Data Syst., 7, 151-167, 2018
https://doi.org/10.5194/gi-7-151-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
07 Jun 2018
Evaluating four gap-filling methods for eddy covariance measurements of evapotranspiration over hilly crop fields
Nissaf Boudhina1,2, Rim Zitouna-Chebbi3, Insaf Mekki3, Frédéric Jacob1,3, Nétij Ben Mechlia2, Moncef Masmoudi2, and Laurent Prévot3 1LISAH, IRD, INRA, Montpellier SupAgro, University of Montpellier, 34060 Montpellier, France
2Institut National Agronomique de Tunisie (INAT)/Carthage University, Tunis, Tunisia
3Institut National de Recherche en Génie Rural, Eaux et Forêts (INRGREF)/Carthage University, Ariana, Tunisia
Abstract. Estimating evapotranspiration in hilly watersheds is paramount for managing water resources, especially in semiarid/subhumid regions. The eddy covariance (EC) technique allows continuous measurements of latent heat flux (LE). However, time series of EC measurements often experience large portions of missing data because of instrumental malfunctions or quality filtering. Existing gap-filling methods are questionable over hilly crop fields because of changes in airflow inclination and subsequent aerodynamic properties. We evaluated the performances of different gap-filling methods before and after tailoring to conditions of hilly crop fields. The tailoring consisted of splitting the LE time series beforehand on the basis of upslope and downslope winds. The experiment was setup within an agricultural hilly watershed in northeastern Tunisia. EC measurements were collected throughout the growth cycle of three wheat crops, two of them located in adjacent fields on opposite hillslopes, and the third one located in a flat field. We considered four gap-filling methods: the REddyProc method, the linear regression between LE and net radiation (Rn), the multi-linear regression of LE against the other energy fluxes, and the use of evaporative fraction (EF). Regardless of the method, the splitting of the LE time series did not impact the gap-filling rate, and it might improve the accuracies on LE retrievals in some cases. Regardless of the method, the obtained accuracies on LE estimates after gap filling were close to instrumental accuracies, and they were comparable to those reported in previous studies over flat and mountainous terrains. Overall, REddyProc was the most appropriate method, for both gap-filling rate and retrieval accuracy. Thus, it seems possible to conduct gap filling for LE time series collected over hilly crop fields, provided the LE time series are split beforehand on the basis of upslope–downslope winds. Future works should address consecutive vegetation growth cycles for a larger panel of conditions in terms of climate, vegetation, and water status.
Citation: Boudhina, N., Zitouna-Chebbi, R., Mekki, I., Jacob, F., Ben Mechlia, N., Masmoudi, M., and Prévot, L.: Evaluating four gap-filling methods for eddy covariance measurements of evapotranspiration over hilly crop fields, Geosci. Instrum. Method. Data Syst., 7, 151-167, https://doi.org/10.5194/gi-7-151-2018, 2018.
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Short summary
To provide reliable time series of evapotranspiration, we evaluated the performances of four different gap-filling methods when tailored to conditions of hilly crop fields. The tailoring consisted of splitting the time series beforehand on the basis of upslope and downslope winds. The obtained accuracies on evapotranspiration after gap filling were comparable to those previously reported over flat and mountainous terrains, and they were better with the most widely used gap-filling method.
To provide reliable time series of evapotranspiration, we evaluated the performances of four...
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