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Factors controlling evaporation and the CO2 flux over an open water lake in southwest of China on multiple temporal scales

Interactions between lakes and the atmosphere are poorly understood, especially for lakes in highland areas. A better understanding of the physical processes controlling turbulent exchange dynamics over lakes is crucial to improve the numerical modelling of the lake–climate interaction. Four years of continuous measurements of energy and CO2 fluxes are conducted over a shallow highland lake (Lake Erhai) in China using eddy covariance (EC) technique from 2012 to 2015. It is found that the latent heat flux (LE) and sensible heat flux (H) has distinct diurnal and seasonal variations. The diurnal H and LE ranges from −31 to 21 W/m2 and from 31 to 171 W/m2, respectively. The heat is stored in the lake from January to June and released from July to the end of the year. The annual total evaporation of Lake Erhai varies from 1120.8 to 1228.5 mm/a, which is always higher than the annual total precipitation. On diurnal scale, the CO2 uptake is observed during most of the midday period. On an annual scale, the Lake Erhai behaves as a net CO2 source, with an annual CO2 budget ranging from 117.5 to 161.7 g C m−2 a−1. The temperature difference (ΔT) between the water surface (T s) and the air temperature (T a), and the product of ΔT and wind speed (U) are the major drivers of H from half‐hourly to monthly scale. The main factors controlling LE are U and the product of U and the vapour pressure difference (VPD) on half‐hourly and daily scales, the total cloud cover, and net radiation (R n) on the monthly scale. Photosynthetic active radiation (PAR) and U has a close relationship with half‐hourly and daily CO2 fluxes, respectively, while annual precipitation and T s has a larger effect on annual CO2 fluxes.