Observing Actual Evapotranspiration within a Hilly Watershed: Case Study of the Kamech Site, Cap Bon Peninsula, Tunisia †
2. Materials and Methods
2.1. Site Description
2.2. Experimental Design and Data Acquisition
2.2.1. Instrumental Design
2.2.2. Meteorological Station
2.2.3. Eddy Covariance Flux Tower
2.3. EC Flux Calculations and Quality Control
2.3.1. Calculating Convective Fluxes
2.3.2. Quality Control
2.4. Characterization of the Climatic Conditions
2.5. Method for Gap Filling EC Data
2.5.1. REddyProc Gap Filling Method
- Step 1: all meteorological data of interest are available (solar incoming radiation Rs, air temperature Ta, and vapor pressure deficit VPD). The missing values of H or λE are replaced by the average value under similar meteorological conditions for a given time window. Similar meteorological conditions correspond to Rs, Ta and VPD values that do not deviate by more than 50 W·m−2, 2.5 °C, 0.5 kPa, respectively. If no similar meteorological conditions are present within a 14 days time window centered on the date of interest, the time window is extended to 28 days.
- Step 2: Rs only is available. The same approach is taken, and similar meteorological conditions correspond to Rs values that does not deviate by more than 50 W·m−2. The time window is 14 days centered on the date of interest.
- Step 3: all meteorological data are missing. The missing value of H or λE are replaced by values derived at the same time of the day from a mean diurnal course (MDC). The latter are computed on the date of interest when possible, or from the two adjacent days otherwise.
2.5.2. Adapting the REddyProc Method to Hilly Cropping Systems
- First, REddyProc was applied in its original version without discriminating the two dominant wind directions (classical way). The obtained gap-filled data were labeled HREP and λEREP.
- Second, REddyProc was applied after discriminating the collected data under conditions of north-west (NW) and south (S) winds. We split the complete time series in two datasets. The NW (respectively S) dataset included the HORI and λEORI data collected under NW (respectively S) wind conditions. REddyProc was applied over each of these two datasets. The two resulting gap-filled datasets were finally merged. The obtained energy fluxes were labeled HRNS and λERNS.
3. Results and Discussion
3.1. Application of REddyProc
3.1.1. Impact of Taking into Account the Wind Direction in REddyProc
3.1.2. Gap Filling Rates Obtained
- In May and June 2010, the LI-7500 analyser experienced a 34 days-long failure, preventing the measurement of λE. REddyProc was able to gap-fill all the missing λE data.
- In December 2010 and January 2011, the flux tower experienced a 41 days-long failure, preventing the measurement of H and λE. REddyProc was able to gap-fill all the missing H and λE data.
- From November 2011 to March 2012, the flux tower experienced several failures, preventing the measurement of H and λE, for 99 and 126 days, respectively. Gap-filling of missing data was only partial, leading to a 99 days long period with no gap filling for both H and λE.
- From October 2012 to May 2013, the flux tower experienced several failures, preventing the measurement of H and λE, for 57 and 224 days, respectively. REddyProc was able to gap-fill all the missing H data, but λE data were not gap-filled during 221 days.
3.2. Seasonal Variations of Daily Surface Fluxes
3.3. Monthly Evapotranspiration
Conflicts of Interest
|λE||latent heat flux|
|asl||above sea level|
|ET0||Penman-Monteith reference evapotranspiration|
|H||sensible heat flux|
|NW||northwest wind sector (220° to 70°)|
|OMERE||french acronym for the Mediterranean Observatory of Water and Rural Environment|
|REP||REddyProc applied without discriminating wind directions (classical way)|
|RNS||REddyProc applied after discriminating wind directions (NW/S)|
|(R)RMSE||(relative) root mean squared error|
|Rs||incoming solar radiation|
|R2||coefficient of determination|
|S||south wind sector (70° to 220°)|
|VPD||water vapour pressure deficit|
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|Years||Number of Days||Number of 30-min Intervals||Missing Raw Measurements||Missing after QC||Missing after Gap-Filling REP||Missing after Gap-Filling RNS|
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Zitouna-Chebbi, R.; Prévot, L.; Chakhar, A.; Abdallah, M.M.-B.; Jacob, F. Observing Actual Evapotranspiration within a Hilly Watershed: Case Study of the Kamech Site, Cap Bon Peninsula, Tunisia. Proceedings 2017, 1, 113. https://doi.org/10.3390/ecas2017-04134
Zitouna-Chebbi R, Prévot L, Chakhar A, Abdallah MM-B, Jacob F. Observing Actual Evapotranspiration within a Hilly Watershed: Case Study of the Kamech Site, Cap Bon Peninsula, Tunisia. Proceedings. 2017; 1(5):113. https://doi.org/10.3390/ecas2017-04134Chicago/Turabian Style
Zitouna-Chebbi, Rim, Laurent Prévot, Amal Chakhar, Manel Marniche-Ben Abdallah, and Frederic Jacob. 2017. "Observing Actual Evapotranspiration within a Hilly Watershed: Case Study of the Kamech Site, Cap Bon Peninsula, Tunisia" Proceedings 1, no. 5: 113. https://doi.org/10.3390/ecas2017-04134