Tomas Ghisi, Milan Fischer, Héctor Nieto, Natalia Kowalska, Georg Jocher, Lucie Homolová, Vicente Burchard-Levine, Zdeněk Žalud, Miroslav Trnka

Study region: Floodplain ecosystem region at the confluence of the Morava and Thaya Rivers, Czech Republic.

Study focus: Accurate determination of actual evapotranspiration (ETa) is essential for understanding surface hydrological conditions. The aim of this study was to evaluate two remote sensing models, METRIC and TSEB, for estimating ETa and energy fluxes in two ecosystems using the eddy covariance (EC) as a reference.

New hydrological insights for the region: Both models demonstrate the ability to quantify ETa across the region. Compared with the METRIC, which had a mean bias error (MBE) = 0.12 mm/day, the TSEB better detected ETa in the forest test site (MBETSEB = -0.03 mm/day). In contrast, the METRIC improved detection of ETa (MBEMETRIC = -0.03 mm/day) in grassland test site, where the TSEB overestimate daily ETa (MBETSEB = 0.52 mm/day). The models and EC indicate similar seasonal dynamics of the evaporative fraction and Bowen ratio throughout the growing season. Despite the overall agreement between the models and EC, the selected spatial outputs indicate some disagreement among them in terms of the spatial patterns of ETa. This disagreement is related to the sensitivity of TSEB to canopy height/roughness, as well as the a priori Priestley-Taylor coefficient in forests. Despite these shortcomings, this study highlights the applicability of remote sensing energy balance-based diagnostic models for studying hydrological processes in a spatially distributed manner.