The long-term tower-based eddy covariance measurements of CO2/H2O fluxes are carried out in a temperate mature forest in Northeast China. The current study investigates the atmospheric (net radiation and vapour pressure deficit) and vegetation (surface conductance) controls of the evapotranspiration (ET) within the two observational years with different water conditions. The results show that the ET during the short dry season of 2004 was higher than that during the wet season of 2005. The ET is mainly driven by the meteorological factor of vapour pressure deficit. The mixed forest did not show clear signs of ET suppression during the summer drought because of its slightly reduced surface conductance, whereas its water demands from the atmosphere significantly increased. Thus, the annual ET slightly varied (416·2 to 462·1 mm) despite the large interannual variation in precipitation (488·7 to 761·6 mm). The 0–100 cm deep soil water storages are important sources of water supply for ET during dry seasons. The findings of this study suggest that the possible reduction in precipitation under future climate change scenarios with invariable or even enhanced ET will decrease the replenishment of groundwater and outflow and, consequently, the downstream water supply. Copyright © 2012 John Wiley & Sons, Ltd.