Environmental and biological controls on the interannual variations of evapotranspiration in a natural oak forest

Investigating the interannual variation (IAV) of evapotranspiration (ET) is important for understanding the water cycle in forest ecosystems. However, there has been little research on interannual variability of ET in warm-temperate forests under a changing environment. In this study, 6-year eddy covariance data (2017–2022) in a warm-temperate natural oak forest in central China were used to examine the IAV of ET and its driving factors. The mean and standard deviation of annual ET from 2017 to 2022 were 610 and 122.8 mm (with a coefficient of variation (CV) of 20 %), respectively. The annual ET did not exhibit an obvious trend over the six years with a larger IAV. Environmental factors had a greater impact on the IAV of annual ET compared to the biological factors, with reference crop evapotranspiration (ET0) exerting the most significant influence on ET. The IAV of monthly ET was primarily controlled by precipitation during the early growing season, but it changed to be controlled by radiation and temperature (i.e., atmospheric evaporation demand) during the mid-growing season. We concluded that atmospheric evaporation demand rather than water supply dominated the IAV of annual ET in the warm-temperate natural oak forest in central China, and occasional seasonal drought only affected the ET in a short time-scale (no more than three years). There is a need to measure three components of ET (transpiration, canopy interception evaporation and soil evaporation) in order to better understand the IAV of ET and the underlying biophysical control mechanisms.