Assessing Utility of Copernicus-Based Evapotranspiration Maps for National Monitoring of Field-Scale Water Use.

Increasing need for fresh water resources, particularly in irrigation, makes it imperative to develop tools to monitor and improve water use efficiency at field, regional and national levels. Satellite observations are highly suitable for this task and for this reason FAO, the custodian agency of Sustainable Development Goals Indicators 6.4.1 and 6.4.2, developed the WaPOR portal through which it distributes satellite-based (Terra and Aqua, PROBA-V and Landsat) evapotranspiration (ET) maps. The aim of this study is to evaluate the suitability of using Copernicus data (Sentinel-2 and Sentinel-3 observations and ERA5 meteorological model) to produce high-resolution, national-scale ET maps during the evolution of WaPOR portal. Results indicate that Copernicus-based maps show generally similar ET patterns to WaPOR maps across climatic and land-use gradients while providing more accurate and detailed field-level estimates compared to MODIS-based WaPOR maps.