Soil water content and soil temperature modeling in a vadose zone of Andosol under temperate monsoon climate

Abstract

Model applications for delivering reliable information on soil water content (θv) and soil temperature (Tsoil) specific to Andosols (Kuroboku) are still limited despite their large area coverage (0.84% of the global terrestrial surface) and great potentials for improving agricultural production. The performance of the HYDRUS-1D model was therefore evaluated by comparing the predicted θv and Tsoil with field observations gathered from the vadose zone of a volcanic ash soil located in Fuchu (western suburb of Tokyo) representative of a temperate monsoon climate. The necessary soil properties to operate the model were obtained from both field and laboratory experiments while climatic data used for the meteorological submodels were extracted from a nearby weather station. A sensitivity and uncertainty analysis leveraging a Monte Carlo method was conducted to identify the soil hydraulic parameters critical to precise and reliable θv, vapor flow, and heat flow simulations. The temporal dynamics of simulated θv and Tsoil in the vadose zone of Andosol during the 365-day period were consistent with the values monitored under field condition demonstrating overall great performance of HYDRUS-1D. Specifying soil layer-specific hydraulic parameters significantly improved the goodness of fits between predicted and measured θv compared to the default simulation in which the surface soil layer was employed for the entire depth assuming a homogeneous profile. Water vapor influence on the total water flux and Tsoil dynamics was negligible during the whole period. Although the magnitudes of sensitivity and the contributions of soil hydraulic parameters to the water flow varied with soil profile and soil water regime, the foremost proportions of uncertainties were from the parameters w2, α2 and n2. While all remaining soil hydraulic parameters significantly contributed to substantial change in the predicted θv, their overall influence was relatively small. The HYDRUS-1D model can be used as effective tool for predicting θv and Tsoil in the vadose zone of Andosols in temperate monsoon environments for decision supporting in agriculture and other sectors such as to optimize water, crop yield and quality. The performance of the model can be greatly increased by setting soil layer-specific hydraulic parameters and focusing on the calibration of w2, α2 and n2.