We use statistical optimization with a hydrologic model to obtain the van Genuchten parameters of a large White Fir tree in a mid-latitude montane forest ecosystem, located in the King's River Experimental Watershed as part of the Southern Sierra Critical Zone Observatory. The site is instrumented for spatially distributed monitoring of soil water content, matric potential and sap flux. The physical tree is represented in a HYDRUS model that models the interactions betweens soil, tree and atmosphere as a continuum. The soil and tree domains are modeled as variably saturated porous media, while atmospheric forcing taken from a nearby flux tower is used to determine the potential evapotranspiration (ET) and root uptake (RU). Actual ET and RU are modeled by accounting for canopy and root distributions together with matric potential stress in the soil-tree domains. This model is embedded within a Markov Chain Monte Carlo (MCMC) framework using current versions of the DREAM_ZS optimization code. We present results of the parameter optimization for time periods in different seasons, analyze the uncertainty and information content in the different measurement methods and use the optimized parameters to study the influence of soil water stress on the soil-root-tree system.
Rings, J., Kamai, T., Mollaei, M., Nasta, P., Vrugt, J.A., Hartsough, P.C., Hopmans, J.W. (2011): Optimization of hydrological parameters in a Soil-Tree- Atmosphere Continuum model of a large White Fir. Fall meeting, American Geophysical Union, December 2011. Abstract H51A-1187. .