Evapotranspiration over a Japanese cypress forest. II. Comparison of the eddy covariance and water budget methods

Evapotranspiration over a Japanese cypress forest was estimated using both the eddy covariance and water budget methods. The long-term water budget revealed that there has been no obvious change in the annual amount of evapotranspiration in this watershed for 33 years despite tree growth, succession, occasional cutting and natural disturbance. Comparison of the eddy covariance method, with a correction for the energy budget, and long-term and short-term water budget methods strongly suggests the validity of the results of both methods and also demonstrates that both the amplitude and characteristics of the seasonal fluctuation of evapotranspiration show no significant interannual differences despite considerable fluctuation in precipitation and hence soil moisture. The three-year average amount of evapotranspiration from the eddy covariance method, with a correction for the energy budget (735 mm) were very close to the 33-year average amount of evapotranspiration from the water budget method (749 mm).