The role of ground heat flux in estimating evapotranspiration by the Penman-Monteith method on mountain meadow

Ground heat flux (G) isoften anoverlooked component ofthe surface energy balance, and its accurate determination remains challenging. Inthe present study, the accuracy ofvarious G estimation methods isexamined using long-term measurements from the Central European mountain meadow. The impact ofdifferent G approximation oncalculated evapotranspiration bythe Penman-Monteith method (ET) isanalysed. Soil heat flux measurements and surface temperature data were used todetermine G, while net radiation was used toapproximate G. Neglecting G led toan overestimation ofET inthe daily timestep. Onthe contrary, the FAO-recommended hourly approximation overestimated G, underestimating ET. Site-specific calibrations ofG prediction models improved their accuracy. For daily average G, aswell asfor hourly average G, simple constant parameter models (i.e., models including asingle parameter specifying the fraction ofnet radiation directly) provide satisfactory accuracy ofET evaluation. However, inan hourly timestep, net radiation fails asapredictor ofG shortly after sunrise and before sunset. The findings emphasise the importance ofconsidering G inET calculations and the need for site-specific calibrations ofG estimation models.