• decoupling coefficient;
  • eddy covariance;
  • evergreen coniferous forest;
  • evapotranspiration;
  • inter-annual variation;
  • surface conductance


Five years (2006–2010) of eddy-covariance data were used to investigate inter-annual variation of evapotranspiration (E) under dry canopy conditions (i.e. no rainfall in the previous 24 h) in summer over a cool-temperate evergreen coniferous forest in Japan. The data included the warmest summer (June to September) in the past 50 years (2010) and the coolest summer in the past 15 years (2009). We found significant differences between 2009 and 2010 in gas exchange properties such as equilibrium evaporation (Eeq) and surface conductance (Gs) in addition to meteorological variables such as air vapour pressure deficit (Da) and net radiation. The values of E, however, were not significantly different in these two years. Furthermore, the inter-annual variation (coefficient of variance, CV) in E was relatively low (3.5%) as compared with higher values of inter-annual variation in gas exchange properties (4.2–10.0%) and meteorological factors (4.3–18.3%). The relatively steady E can be explained by (1) less effective atmospheric demand (i.e. less sensitive to Eeq) because of the low decoupling coefficient (0.07–0.15) at the study site and (2) the negative response of Gs to Da and a reduced sensitivity of E to high Da values in relation to plant physiological regulation (i.e. stomatal control). Copyright © 2013 John Wiley & Sons, Ltd.