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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 20, issue 4
Hydrol. Earth Syst. Sci., 20, 1509–1522, 2016
https://doi.org/10.5194/hess-20-1509-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Hydrol. Earth Syst. Sci., 20, 1509–1522, 2016
https://doi.org/10.5194/hess-20-1509-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Apr 2016

Research article | 20 Apr 2016

Stem–root flow effect on soil–atmosphere interactions and uncertainty assessments

Tzu-Hsien Kuo1, Jen-Ping Chen1, and Yongkang Xue2 Tzu-Hsien Kuo et al.
  • 1Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan, Republic of China
  • 2Department of Atmospheric and Oceanic Sciences, and Department of Geography, University of California, Los Angeles, California, USA

Abstract. Rainfall that reaches the soil surface can rapidly move into deeper layers in the form of bulk flow through the stem–root flow mechanism. This study developed the stem–root flow parameterization scheme and coupled this scheme with the Simplified Simple Biosphere model (SSiB) to analyze its effects on land–atmospheric interactions. The SSiB model was tested in a single-column mode using the Lien Hua Chih (LHC) measurements conducted in Taiwan and HAPEX–Mobilhy (HAPEX) measurements in France. The results show that stem–root flow generally caused a decrease in soil moisture in the top soil layer and moistened the deeper soil layers. Such soil moisture redistribution results in substantial changes in heat flux exchange between land and atmosphere. In the humid environment at LHC, the stem–root flow effect on transpiration was minimal, and the main influence on energy flux was through reduced soil evaporation that led to higher soil temperature and greater sensible heat flux. In the Mediterranean environment of HAPEX, the stem–root flow substantially affected plant transpiration and soil evaporation, as well as associated changes in canopy and soil temperatures. However, the effect on transpiration could be either positive or negative depending on the relative changes in the soil moisture of the top soil vs. deeper soil layers due to stem–root flow and soil moisture diffusion processes.

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The stem-root flow mechanism was parameterized and incorporated into the Simplified Simple Biosphere model to analyze its impact on soil moisture and land-atmospheric interactions. By testing against the Lien Hua Chih (Taiwan) and HAPEX-Mobilhy (France) measurements, the model shows that stem-root flow reduced the top-soil moisture content and moistened the deeper soil layers. Such soil moisture redistribution results in significant changes in heat flux exchange between land and atmosphere.
The stem-root flow mechanism was parameterized and incorporated into the Simplified Simple...
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