An analysis of summer evapotranspiration based on multi‐year observations including extreme climatic conditions over a cool‐temperate evergreen coniferous forest, Takayama, Japan

Abstract

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.

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

“…Barr et al ., ; Thomas et al . ; Saitoh et al ., ; Xie et al ., ). Further long‐term continuous flux and meteorological measurements could be useful to clarify the impacts of recent significant trends of rainfall characteristics (e.g.…”

“…The variability in ET was similar to other forests (e.g. Kosugi et al ., ; Kume et al ., ; Saitoh et al ., ; Xie et al ., ). In a Bornean tropical forest, Kume et al .…”

“…In a cool‐temperate Japanese cedar forest, Saitoh et al . () conducted eddy covariance flux measurements and reported that the inter‐annual variation (CV) of ET in the dry canopy was 3.5%. Xie et al .…”

“…Some studies have reported inter‐annual variations of ET and the factors causing those variations based on long‐term continuous flux measurements (e.g. Barr et al ., ; Thomas et al ., ; Saitoh et al ., ). According to previous studies, soil drought caused by variability in rainfall may be a factor that determines the inter‐annual variations in ET as a result of stomatal closure (Wilson and Baldocchi, ; Barr et al ., ; Granier et al ., ; Thomas et al ., ; Xue et al ., ).…”

“…Barr et al (2007) reported that annual ET ranged from 313 to 517 mm for 9 years in a boreal aspen forest, including a 3-year period of severe drought. In addition, relatively conservative levels of ET were observed during 2 years of extreme climatic conditions, including the warmest summer in the past 50 years and the coolest summer in the past 15 years, in a cool-temperate evergreen coniferous forest; this occurred because the regulation of atmospheric demand was less effective owing to stomatal control (Saitoh et al, 2013). In these previous studies, the long-term trends in ET have been explained simply by the empirical relationships between ET and environmental factors such as vapour pressure deficit and air temperature.…”