Rehana Khatun, Takeshi Ohta, Ayumi Kotani, Jun Asanuma, Minoru Gamo, Shijie Han, Takashi Hirano, Yuichiro Nakai, Nobuko Saigusa, Kentaro Takagi, Huimin Wang and Natsuko Yoshifuji
Release Date: December 17, 2011

Spatial variations in evapotranspiration over East Asian forest sites. I. Evapotranspiration and decoupling coefficient

Rehana Khatun1), Takeshi Ohta1), Ayumi Kotani1), Jun Asanuma2), Minoru Gamo3), Shijie Han4), Takashi Hirano5), Yuichiro Nakai6), Nobuko Saigusa7), Kentaro Takagi8), Huimin Wang9) and Natsuko Yoshifuji10)

1 ) Graduate School of Bioagricultural Sciences, Nagoya University
2 ) Terrestrial Environment Research Center, Tsukuba University
3 ) National Institute of Advanced Industrial Science and Technology
4 ) Institute of Applied Ecology, Chinese Academy of Sciences
5 ) Graduate School of Agriculture, Hokkaido University
6 ) Forestry and Forest Products Research Institute
7 ) National Institute for Environmental Studies
8 ) Field Science Center for Northern Biosphere, Hokkaido University
9 ) Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences
10 ) Graduate School of Agriculture, Kyoto University

(Received: June 27, 2011)
(Accepted for publication: November 24, 2011)

Abstract:
Evapotranspiration (ET) is not only a vital component of water budget, but also plays an important role in the energy budget of the earth-atmospheric system, ultimately driving many regional and global scale climatological processes. This paper describes the ET characteristics and factors controlling ET across the 17 forest sites in East Asia (2°S to 64°N latitude). ET was measured using the eddy covariance technique at each site. Daytime dry-canopy data for the growing season were used in this study. Growing season mean ET gradually decreased as latitude increased, with a range of 4.4 to 1.2 mm d−1. The growing season mean decoupling coefficient (Ω) ranged from 0.42 to 0.11 across the studied sites. At low-latitude forest sites, Ω was close to 0.50, indicating that the bulk surface was partially decoupled from the atmosphere and ET was strongly controlled by net radiation and vapour pressure deficit. At high-latitude forest sites, Ω was low (∼0.12), indicating that the bulk surface was well coupled to the atmosphere and ET was mainly controlled by surface conductance. The value of Ω was determined mainly by the ratio of aerodynamic conductance to surface conductance across the studied forests of East Asia.

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To cite this article:
Rehana Khatun, Takeshi Ohta, Ayumi Kotani, Jun Asanuma, Minoru Gamo, Shijie Han, Takashi Hirano, Yuichiro Nakai, Nobuko Saigusa, Kentaro Takagi, Huimin Wang and Natsuko Yoshifuji: “Spatial variations in evapotranspiration over East Asian forest sites. I. Evapotranspiration and decoupling coefficient”, Hydrological Research Letters, Vol. 5, pp.83-87, (2011) .

doi:10.3178/hrl.5.83
JOI JST.JSTAGE/hrl/5.83
Copyright (c) 2011 Japan Society of Hydrology and Water Resources