This dataset provides derived measurements of land-atmosphere energy and water exchanges from selected COSMOS-UK environmental monitoring sites across the United Kingdom, collected between 2014 and 2024. It contains estimates of sensible heat flux (H), latent heat flux (LE), and evapotranspiration (ET), alongside supporting hydrometeorological and soil physics variables, enabling detailed analysis of surface energy balance and water fluxes. The data cover 45 COSMOS-UK sites, where a 3D sonic anemometer is installed and operational, mobile telemetry is available, and no relevant instrumentation or telemetry faults are present. These sites are distributed across a range of UK land cover types, supporting regional and cross-site comparison of land-atmosphere processes. Measurements are provided at sub-daily resolution, with evapotranspiration and associated variables calculated at 30-minute intervals. The dataset spans the operational periods of eligible sites and takes into account changes in site configuration and land use over time. Fluxes are derived from high-frequency (20 Hz) wind component and sonic temperature measurements using specialist processing software (EddyPro Software v7.0.9, LI-COR Biosciences). The dataset includes site metadata, flux and ancillary variables (both quality-controlled and non-quality-controlled), dynamic metadata documenting instrumentation and land cover changes, and a dictionary describing all variables. These data support applications such as evaluating and driving land-surface and hydrological models, comparing observations across sites and networks, and improving understanding of land-atmosphere interactions relevant to floods, droughts, and water balance studies. Full details about this dataset can be found at https://doi.org/10.5285/c0b5caf4-c14a-49e8-a720-2401c8d3d135
