Simulation of soil water & heat transport in a vegetated field using a coupled program of the canopy energy budget model and HYDRUS-1D

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  • 群落熱収支モデルとHYDRUS-1Dの連結プログラムを用いた 畑地の土壌水分量・ 地温予測モデルの構築
  • 群落熱収支モデルとHYDRUS-1Dの連結プログラムを用いた畑地の土壌水分量・地温予測モデルの構築 : ダイズ栽培圃場における蒸発・蒸散の配分割合の検討
  • グンラク ネツ シュウシ モデル ト HYDRUS-1D ノ レンケツ プログラム オ モチイタ ハタチ ノ ドジョウ スイブンリョウ ・ チオン ヨソク モデル ノ コウチク : ダイズ サイバイ ホジョウ ニ オケル ジョウハツ ・ ジョウサン ノ ハイブン ワリアイ ノ ケントウ
  • Investigation of partitioning evapotranspiration in a soybean field
  • ダイズ栽培圃場における蒸発· 蒸散の配分割合の検討

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Abstract

Evapotranspiration plays an important role to investigate simultaneous movement of water and heat in a vegetated field. To simulate changes of soil water content and soil temperature using the Richards equation with root water uptake, partitioning potential evapotranspiration, Ep, into potential soil surface evaporation, Egp, and crop transpiration, Ecp, is necessary. The double source model, one of the canopy energy budget models calculating energy balances at both canopy and soil surface, is a promising model to calculate evaporation rate, Eg, and transpiration rate Ec, separately. In this study, we developed a numerical model to simulate water movement and heat transport in the root zone by implementing the double source model in HYDRUS-1D. Field observation was also carried out in a soybean field to test the developed model. Simulated soil water contents and temperatures using various values of radiation transmissivity, τ, were compared with observed data during relatively wet condition. It was indicated that determining τ based on observed surface coverage, Sc (i.e., τ = 1 - Sc) can be a reasonable method to partition Ep to Egp and Ecp with considering crop growth. Simulation for a longer drying period was also carried out to show changes of Eg, Ec, and energy balance components at both canopy and soil surface. Eg decreased more rapidly than Ec, resulting in increase of soil temperature amplitude due to increased soil heat flux. Agreements between simulated soil water contents and temperatures and observed ones improved by accounting for the compensated root water uptake and larger unsaturated hydraulic conductivity for drier range, due to increasing root water uptakes and evaporation rates. For proper evaluation of the ratio of Eg and Ec in dry period, detail investigations for soil hydraulic property and root water uptake property are needed.

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