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

Introduction

Actual Evapotranspiration (ET_a), is the main component required to understand both hydrological and ecological processes between the land surface and the atmosphere. Reliable spatio-temporal distribution of ET is important for water resources planning, management and monitoring, efficient irrigation scheduling, and climate change mitigation scenarios. Due to complex land-plant-atmosphere interactions and natural variability in topography, soil moisture and vegetation type, obtaining accurate information on ET is the most challenging among all components of the hydrologic cycle, especially in agroecosystems where water is scarce or fluctuates seasonally.

There are several conventional field methods used to determine ET_a, 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 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 (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 ET_a, 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 imitations 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 ET_a field measurements established through this ET-Network could effectively be used to validate and calibrate the remote sensed based estimations.

For the Regional ET-Network (having Egypt, Jordan, Lebanon, Morocco, and Tunisia as initial countries), the Penman Monteith method will be adopted as a standard for field ET_a determinations, while the eddy covariance, the lysimeter and the soil-moisture methods will be used to test and calibrate the Penman Monteith method on different vegetated surfaces.

The climatic and crop variables needed for the Penman Monteith method are derived through the Cordoba-ET system (an enhanced agro-meteorological station) which was recently developed by Cordoba University, Spain.

The present training workshop is thus organized to provide the necessary common knowledge for an effective Regional ET-Network

Objective

To build a common capacity of the local institutions on ET_a measurements, in the field and through RS, on accuracy assessments of RS ET_a data of different databases and on their analysis and use for agricultural-related applications (e.g., water accounting, water productivity, water management, etc.). To achieve this, a comprehensive training program will be organized so that national staff will be able to collect, analyse and use the data on the ground. After this training, ICARDA will provide the technical backstopping to make sure that instruments installation, data measurement, analysis and dissemination are conducted in a correct and unified way in all participating countries. In this training, we will focus on the ET measurements using energy balance methodologies with a special focus on Cordoba-ET system. The training will cover the Cordoba-ET system, data collection, analysis and dissemination as a standardized validation protocol as well as from the other field ET_a methods of determination.

Expected outcomes

• Participants became fully aware of the ET-Network standard protocol (Cordoba methodology) and they can properly and accurately collect, analyse and disseminate the obtained data to relevant stakeholders for better regional water planning
• ET-Network members communicated with each other to exchange generated data and knowledge
• The generated knowledge will serve for better water planning and management