Evapotranspiration dynamics and their drivers in a temperate mixed forest in northeast China

Abstract

Evapotranspiration (ET) is a vital part of the global water cycle and is closely related to carbon sequestration. Analysing ET dynamics and their drivers would benefit for improving our understanding of the global water and carbon cycles. Using an eddy covariance (EC) approach, we analysed ET dynamics and their drivers in a temperate mixed forest over northeast China from 2016 to 2017. The results showed that 43.55% of our eddy covariance data passed the quality control. In addition, the energy balance ratio was 0.62, indicating that measurements were reliable. The measured ET showed clear single peak patterns with seasonal and diurnal variations. The daily ET ranged from 0 to 7.75 mm d−1 and the hourly ET ranged from 0 to 0.28 mm h−1. The ranges of hourly ET floated from 0 to 0.05 mm h−1 at non-growing season (November to April) while ranged from 0 to 0.28 mm h−1 at active growing season (May to October). The diurnal ET dynamics during the non-growing season were driven by air temperature (Ta), but were governed by global radiation (Rg) during the active growing season. Leaf area index (LAI) comprehensively reflected the variations of Ta and Rg, and was found to be the primary factor shaping the seasonal dynamics of ET. The annual ET rates were 501.91 ± 5.30 mm year−1 and 554.60 ± 11.24 mm year−1 for 2016 and 2017, respectively. Therefore, energy supply, represented by Ta and Rg, governed ET dynamics in our temperate mixed forest, while variables representing the energy supply affecting ET dynamics differed among seasons and time scales. ET dynamics indicated that a temperate mixed forest is important to the global water cycle. Our results improved our understanding of ET dynamics in the studied region.