Evapotranspiration and runoff in a forest watershed, western Japan



A Note has been published for this article in Hydrological Processes 18(4) 2004, 825.

Both water and heat balances were studied in a conifer plantation watershed in south-west Japan, within the warm-temperate East Asia monsoon area. Forest cover in the watershed consists mainly of Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa) plantations. Precipitation and runoff have been observed since 1991, so evapotranspiration can be compared with the water balance. Two meteorological observation towers were built to monitor evapotranspiration in the watershed. The annual average precipitation, amount of runoff and losses were 2166, 1243 and 923 mm, respectively. The evapotranspiration (latent heat flux) agreed well with the water balance losses. The average annual evapotranspiration at the tower built in the centre of the watershed was 902 mm; evapotranspiration at the other tower, further upslope, was 875 mm. The observed evapotranspiration was 39% to 40% of the average precipitation (2166 mm). The mean net radiation was c. 2·6 GJ m−2 year−1, and is considered a representative value of the net radiation (Rn) in coniferous plantations in this region. This region is classified in the humid zone based on the ratio of net radiation (Rn) to the energy required to evaporate the rainfall (λR). The mean annual evaporation of canopy-intercepted water was 356 mm or about 15% of the average precipitation. Copyright © 2003 John Wiley & Sons, Ltd.