Assessing the consistency of eddy covariance measurements under conditions of sloping topography within a hilly agricultural catchment

Zitouna-Chebbi, Rim; Prévot, Laurent; Jacob, Frédéric; Mougou, R.; Voltz, Marc

doi:10.1016/j.agrformet.2012.05.010

Cited by 25 publications

(45 citation statements)

References 45 publications

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“…(IAO, 2002). From downstream to upstream, the mean annual rainfall and the mean annual evapotranspiration (Penman-Monteith reference crop) range from 450 mm to 800 mm and from 1000 to 1500 mm, respectively (IAO, 2002;Zitouna-Chebbi et al, 2012). The Lebna watershed is subject to soil erosion and subsequent reservoir siltation (IAO, 2002;Gaubi et al, 2016).…”

Section: Impact Of Farmland Fragmentation On Rainfed Crop Allocation Inmentioning

confidence: 99%

Impact of farmland fragmentation on rainfed crop allocation in Mediterranean landscapes: A case study of the Lebna watershed in Cap Bon, Tunisia

et al. 2018

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Section: Impact Of Farmland Fragmentation On Rainfed Crop Allocation Inmentioning

confidence: 99%

Impact of farmland fragmentation on rainfed crop allocation in Mediterranean landscapes: A case study of the Lebna watershed in Cap Bon, Tunisia

et al. 2018

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“…These tests permitted to ensure that the theoretical requirements for the EC measurements were fulfilled [27]. On the same site, [21,22] applied these tests over EC datasets collected under conditions of hilly topography, and reported good energy balance closure for the selected data. We kept the high and good quality classes as defined by [28] and [29], since these two classes are considered as suitable for long-term observations.…”

Section: Quality Controlmentioning

confidence: 99%

“…Third, as the flux tower was located near the bottom of the northern rim of the Kamech watershed, NW winds induced descending air flows, whereas S winds induced ascending air flows. On the same hilly site, [21,22] highlighted the importance of considering the wind direction when conducting eddy covariance flux measurements. Therefore, the REddyProc gap-filling procedure was applied in two different manners: without or with discriminating between the two dominant wind directions (see section 2.5.2).…”

Section: Impact Of Taking Into Account the Wind Direction In Reddyprocmentioning

confidence: 99%

“…First, the combined effects of hilly topography and wind direction induced changes in airflow streamlines and turbulent fluxes [23]. Second, when observing fluxes at the field scale in the same study area, [21] and [22] reported the existence of two dominant wind directions, and demonstrated the necessity to discriminate these two wind directions when processing the EC data. Thus, the gap filling methods are likely to provide different relationships between ancillary information and flux measurements, when considering different wind directions.…”

Section: Introductionmentioning

confidence: 99%

“…For hilly and heterogeneous cropping systems, the conditions that drive ETa (i.e., radiative, wind and turbulence regimes, vegetation patterns) can be different from those occurring for homogenous surfaces over flat / mountainous areas. For instance, it is necessary to adapt correction methods for EC measurements [21,22], or to account for footprint changes according to wind direction.…”

Section: Introductionmentioning

confidence: 99%

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Observing Actual Evapotranspiration within a Hilly Watershed: Case Study of the Kamech Site, Cap Bon Peninsula, Tunisia

Zitouna-Chebbi

Prévot

Chakhar

et al. 2017

Proceedings of the 2nd International Electronic Conference on Atmospheric Sciences

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There is a strong need for long term observations of land surface fluxes, especially the latent heat flux (λE), or actual evapotranspiration (ETa), a key component of both the surface energy balance and the hydrological cycle. The eddy covariance (EC) method is widely used to provide measurements of land surface fluxes. However, missing data are inherent to EC measurements and several gap-filling methods have been proposed. Nevertheless, observing ETa by EC and testing gap-filling methods in hilly watersheds received little attention. This study aimed at obtaining continuous ETa time series from EC measurements collected within a small hilly watershed, which implied adapting gap-filling techniques to these particular conditions. The experiment took place within the agricultural watershed Kamech (Northeast Tunisia) which belongs to the OMERE environmental observatory. A 9.6-meter-high EC flux tower was installed in the center of the 2.45 km 2 area watershed. Sensible and latent heat fluxes data collected from 2010 to 2013 were quality controlled. The software REddyProc was used to gap-fill the fluxes at hourly timescale. To account for the combined effects of wind direction and topography, REddyProc was applied after separating the two dominant wind directions, which notably improved the estimated fluxes. Aggregating the hourly λE estimates at daily and monthly timescales allowed analyzing the temporal variability of ETa over the seasons and between years.

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Accounting for vegetation height and wind direction to correct eddy covariance measurements of energy fluxes over hilly crop fields

et al. 2015

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As agricultural hilly watersheds are widespread throughout the world, there is a strong need for reliable estimates of land surface fluxes, especially evapotranspiration, over crop fields on hilly slopes. In order to obtain reliable estimates from eddy covariance (EC) measurements in such conditions, the current study aimed at proposing adequate planar fit tilt corrections that account for the combined effects of topography, wind direction, and vegetation height on airflow inclinations. EC measurements were collected within an agricultural hilly watershed in northeastern Tunisia, throughout the growth cycles of cereals, legumes, and pasture. The wind had two dominant directions that induced upslope and downslope winds. For upslope winds, the airflows were parallel to the slopes and slightly came closer to the horizontal plane when vegetation grew. For downslope winds, over fields located in the lee of the rim top, the airflows were almost horizontal over bare soil and came closer to the topographical slope when vegetation grew. We therefore adjusted the planar fit tilt correction on EC measurements according to vegetation height and by discriminating between upslope and downslope winds. This adjusted tilt correction improved the energy balance closure in most cases, and the obtained energy balance closures were similar to that reported in the literature for flat conditions. We conclude that EC data collected within crop fields on hilly slopes can be used for monitoring land surface fluxes, provided planar fit tilt corrections are applied in an appropriate manner.

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Assessing the consistency of eddy covariance measurements under conditions of sloping topography within a hilly agricultural catchment

Cited by 25 publications

References 45 publications

Impact of farmland fragmentation on rainfed crop allocation in Mediterranean landscapes: A case study of the Lebna watershed in Cap Bon, Tunisia

Impact of farmland fragmentation on rainfed crop allocation in Mediterranean landscapes: A case study of the Lebna watershed in Cap Bon, Tunisia

Observing Actual Evapotranspiration within a Hilly Watershed: Case Study of the Kamech Site, Cap Bon Peninsula, Tunisia

Accounting for vegetation height and wind direction to correct eddy covariance measurements of energy fluxes over hilly crop fields

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