Results Time Study Site Measured data Alfalfa Numerical Analysis of Water and Heat Transport in Vegetated Soils Using HYDRUS-1D Masaru Sakai 1), Jirka Šimůnek 2) 1)Dept. Plants, Soils, and Climate, Utah State University, Logan 2) Dept. Environmental Sciences, University of California, Riverside Introduction Summary Evaluation of water contents and temperatures in root zone is important for water management of agricultural fields. To simulate water flow, heat transport, and root water uptake simultaneously, the boundary condition at vegetated soil surface evaluated from available meteorological information is necessary. The objective of study is to develop a numerical model that solves water flow, heat transport, and root water uptake with surface energy and water balance. We implemented “Double-Source Model” (Watanabe, 1992), that calculate energy balance at the crop canopy and the soil surface, to the HYDRUS-1D code. Calculated soil temperatures were compared with observed data in a field site. Double -Source Model (Watanabe, 1994)  Calculated energy balance component at the soil surface. Every term decreases with time corresponding to Alfalfa growth.  Observed and Calculated soil temperature. Calculated results show larger daily amplitudes than observed ones.  The Double-Source Model was implemented in the HYDRUS-1D code, and the energy balance at the soil surface are calculated from meteorological information.  Although calculated soil temperature reasonably agreed with observed one, daily amplitude was larger. Further investigations of parameters in the energy balance equations are needed. Numerical Simulation Water and vapor Flow Heat Transport Energy balance at Crop canopy Energy balance at Soil surface R s :Incoming shortwave radiation R l↓ :Downward longwave radiation G :Surface heat flux T c :Air temperature T s : Soil surface temperature T c : Crop canopy temperature  s :Soil surface emissivity  c :Crop canopy emissivity  s :Soil surface albedo [-]  c :Crop canopy albedo [-] L :Latent heat of vaporization Evaporation E s and Transpiration rate E c Sensible heat flux from soil surface H s and canopy H c r as :Resistance for vapor at soil surface r ac :Resistance for vapor at canopy r hs :Resistance for heat at soil surface r hc :Resistance for heat at canopy r s :Soil surface resistance  s :Vapor density at soil surface  a :Atmospheric vapor density  vs (T c ) :Saturation vapor density at canopy  :Stefan-Boltzman constant C a :Volumetric heat of air E s and G for surface boundary conditions from meteorological data Surface Cover Fraction SCF Field data Boundary Conditions Sandy Loam 70 cm Sand 80 cm Silt Loam 0 cm (Segal et al., 2008) Solar Radiation Relative Humidity Wind Speed Air Temperature Irrigation rate (every 15 minutes) Alfalfa Field in San Jacinto, California (33º55'22''N, 117º00‘46''W) 220 cm depth water table Soil temperature Pressure head References Watanabe, T. (1994): Bulk parameterization for a vegetated surface and its application to a simulation of nocturnal drainage flow. Boundary-Layer Meteorol., 70: Segal, E., S.A. Bradford, P. Shouse, N. Lazarovitch, and D. Corwin (2008): Integration of hard and soft data to characterize field-scale hydraulic properties for flow and transport studies, Vadose Zone Journal., 7: Alfalfa was harvested July 24th and grew up after July 25th Reference values were used for crop height and root depth July 25th – September 2nd  Calculated evaporation rate from soil surface and transpiration rate from canopy. Surface heat flux B.C. for heat transport Evaporation rate B.C. for water flow Transpiration rate Root water uptake HYDRUS Interface  Calculated profiles of pressure head, water content, and root water uptake. Aerodynamic Resistance Between soil and atmosphere Between entire surface (soil and canopy) and atmosphere Between canopy and atmosphere u :Wind speed k :Karman constant (=0.41) z ref :Reference height d :Zero-plane displacement height z h, z m :Surface roughtness for heat flux and momentum  h,  m :Atmospheric stability correction factor  Relationship between resistances and SCF