Establishing and Operating a Regional Network for Field Measurement of Actual Crop Water Consumption (Evapotranspiration)

Abstract

There are several conventional field methods used to determine ETa, including: 1) the Eddy covariance/energy balance method; 2) the Bowen-ratio/energy balance method; 3) Weighing lysimeters; 4) Soil-moisture depletion method; 5) Large Aperture Scintillometer; and 6) the Penman Monteith method. These methods have their own specific advantages and limitations based on the theory behind and on the instrumentation requirements. However, what they have in common is, among others, the restricted sampling area and the complexity and extremely high costs when attempting to scale-up to larger areas. For large scales (e.g., irrigation schemes, watershed, sub-national, national and basin scales) the only feasible and affordable methods for ET determination are through satellite Remote Sensing (RS), due to progress and advances in space science in recent years. There are several well-established RS-based algorithms for the determination of ETa, including SEBAL (Surface Energy Balance Algorithm for Land), METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration), SEBS (Surface Energy Balance System), ETLook, ETMonitor, etc. Unfortunately, also these methods have their own specific advantages and limitations and are all suffering from a generally limited and scattered field validation. Virtually no validations are systematically carried out in the NENA Region. Therefore, the ETa field measurements established through this ET-Network could effectively be used to validate and calibrate the remote sensed based estimations.