Utility of Copernicus-Based Inputs for Actual Evapotranspiration Modeling in Support of Sustainable Water Use in Agriculture

Abstract

Quantifying spatial and temporal patterns of actual evapotranspiration (ET) using earth observation data can significantly contribute to accurate and transparent monitoring of Sustainable Development Goals (SDG) target 6.4, which focuses on increase of water use efficiency and sustainable fresh water withdrawals. Irrigated agriculture is by far the largest consumer of fresh water worldwide and evapotranspiration can serve as direct proxy of crop water use. Various ongoing initiatives encourage use of remote sensing data for monitoring of SDG 6.4, including WaPOR portal run by the Food and Agriculture Organization of the United Nations. However, none of those initiatives use Copernicus satellite and modelled data to the fullest extent. Copernicus provides operational high-quality data freely and openly, contains all the inputs required for ET modelling and has long-term continuity and evolution plans, thus allowing for establishment of baseline for SDG 6.4 and continuous monitoring in mid- and long-term. In this study, we evaluate utility of Copernicus data for this task with WaPOR products serving as a comparison benchmark. Thus the modelled ET has to be able to accurately capture field-scale activity at 10-day timesteps while also scaling to national coverage and providing consistent estimates at different spatial resolutions, ranging from tens to hundreds of meters. Results indicate that Copernicus-based ET can reach a correlation of 0.9, mean bias of 0.3 mm/day and root mean square error of less than 1 mm/day when compared against field lysimeter and eddy covariance measurements and, with proper approach, can achieve better spatial-scale consistency than WaPOR d