Comparing evapotranspiration rates estimated from atmospheric flux, soil water balance and FAO56 method in a small orange orchard in Tunisia

摘要

In Tunisia, citrus is suffering from water scarcity and increasing salinity. Its water consumption should be well documented to allow the optimization of irrigation management. Evapotranspiration measurements by Eddy covariance method are trustable and widely used nowadays but its application to small areas with windbreaks is questionable. In Cap Bon region, citrus orchards are small and with windbreaks. The objective of this study is to assess eddy covariance measurements of an orange orchard in presence of a windbreak and to compare the estimated evapotranspiration rates to soil water balance and FA056 approach. An experiment was conducted in northeastern Tunisia, on a 14-year-old navel orange orchard. It is drip irrigated, has an area of 0.4 ha and Cupressus trees are used as a windbreak. An Eddy covariance station was installed since December 2013. The four energy balance components were measured by: a three dimensional sonic anemometer, an optical hygrometer, a net radiometer and soil heat plates. To calculate turbulent fluxes, wind speeds, air temperature and humidity were acquired and stored at 20 Hz. During the year 2014, soil water content was measured by gravimetric technique. The hourly energy surface fluxes were assessed through control quality tests for different wind direction. The energy balance is generally well closed. The imbalance was discussed for wind direction and climatic conditions. Finally, a comparison of evapotranspiration rates estimated from atmospheric measurement tothe ones determined by the soil water balance and the FA056 approach was discussed.