Gap-Filling for Daily Latent Heat Flux Observations with the Full-factorial method at Global Flux Sites.

Latent heat flux (LE) plays a crucial role in the water-energy cycle. Eddy covariance (EC) measurements of LE frequently suffer from data gaps due to weather or equipment malfunctions. This study presents a novel framework combining median-adjusted full-factorial and iterative methods to fill LE data gaps. The findings indicate that the framework exhibits stable gap-filling across land surfaces, showing RMSEs of 14.69-19.51 W/m2 for isolated gaps and averaging 24.41 W/m2 for long-term missing periods (5-50 days). Gap-filled LE data closely matched temporal dynamics and fluctuations of adjacent measurements. Based on gap-filled LE data, all sites demonstrated strong correlations between available energy and turbulent fluxes, with RMSE values ranging 28.41-38.01 W/m2 and achieving an average energy closure of 0.79 across sites. Compared to ERA5-Land and GLEAM products, the gap-filled data significantly outperformed both LE products. Overall, the filled LE data are of high quality and significantly improve the usability of observed data. The complete time-series data from 265 sites (1509 site-years) are valuable for LE model validation and water demand assessments.