Journal of the Japanese Society of Soil Physics
Online ISSN : 2435-2497
Print ISSN : 0387-6012
Water and heat transport in a root zone during evapotranspiration using the canopy energy budget model
Masaru SAKAI
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2022 Volume 151 Pages 35-47


To simulate soil water contents and tempera-tures in a root zone, understanding of root uptake charac-teristics and unsaturated hydraulic conductivity K is nec-essary. In this study, numerical simulations of soil water and heat transport were conducted for a soil drying pro-cess with evapotranspiration in a soybean field, using a coupled program of HYDRUS-1D and a canopy energy budget model. Impacts of K, compensatory water uptake, and water uptake distribution β (z) on simulated soil water contents and temperatures were evaluated comparing with field observed data. Two β (z) distributions, uniform dis-tribution βuni and observed root density based-distribution βRD, were tested. K, controlling soil surface evaporation rate Eg, indicated a considerable impact on soil tempera-tures. In a case with large surface coverage, simulated tem-peratures agreed well with observed ones when relatively large K was used and Eg under the canopy occurred with the potential evaporation rate. By simulating with com-pensatory water uptake, water uptake rates S increased at well-watered lower part of the zoot zone. Although S dis-tributions were different between βuni and βRD, simulated water contents agreed well with observed ones for both cases when root adaptability factor ωc = 0 was used (fully compensated). It indicated that the sensitivity of β (z) to soil water content and temperature was much smaller than K and compensatory uptake. To simulate soil water con-tent changes for relatively shallow root zones, using a uni-form distribution for β (z) and full compensatory uptake (ωc = 0) can be one simple and useful assumption. And applying soil water and heat transport model to field ob-served data to determine average K of the root zone is a promising method for further detailed analysis of soil sur-face evaporation and transpiration.

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