Inter-annual variations and factors controlling evapotranspiration in a temperate Japanese cypress forest

This study was undertaken to evaluate the effects of climatic variability on inter-annual variations in each component of evapotranspiration (ET) and the total ET in a temperate coniferous forest in Japan. We conducted eddy covariance flux and meteorological measurements for 7years and parameterized a one-dimensional multi-layer biosphere-atmosphere model (Kosugi et al., ) that partitions ET to transpiration (Tr), wet-canopy evaporation (E_wet), and soil evaporation (E_soil). The model was validated with the observed flux data. Using the model, the components of ET were estimated for the 7years. Annual precipitation, ET, Tr, E_wet, and E_soil over the 7years were 1536±334mm, 752±29mm, 425±37mm, 219±34mm, and 108±10mm, respectively. The maximum inter-annual fluctuation of observed ET was 64mm with a coefficient of variance (CV) of 2.7%, in contrast to relatively large year-to-year variations in annual rainfall (CV=20.1%). Tr was related to the vapour pressure deficit, incoming radiation, and air temperature with relatively small inter-annual variations (CV=8.2%). E_soil (CV=8.6%) was related mainly to the vapour pressure deficit. E_wet was related to precipitation with large inter-annual variations (CV=14.3%) because of the variability in precipitation. The variations in E_wet were counterbalanced by the variations in Tr and E_soil, producing the small inter-annual variations in total ET.