HR: 17:25h
AN: H34E-06    [Abstracts]
TI: Calibration of a Soil Water Uptake Model Using Model Ensemble and Prior Information in a Semiarid Environment Using Global and Local Search Methods
AU: * Maneta Lopez, M P
EM: mpmaneta@ucdavis.edu
AF: Dept of Land, Air & Water Resources. University of California, Davis, One Shields Ave, Davis, CA 95616, United States
AU: Wallender, W W
EM: wwwallender@ucdavis.edu
AF: Dept of Land, Air & Water Resources. University of California, Davis, One Shields Ave, Davis, CA 95616, United States
AU: Schnabel, S C
EM: schnabel@unex.es
AF: Dept of Geography. Universidad de Extremadura, Campus Universitario s/n, Caceres, 10071, Spain
AB: A common model used to simulate actual evapotranspiration in watershed scale hydrologic models is the Kristensen and Jensen model (e.g. Mike She or MODHMS models). While the Kristensen and Jensen model was originally developed for Nordic climates, it has been extensively used in other types of environments without specific calibration or testing of its performance in climates other than the one for which the model was developed. In semiarid watershed hydrology, evapotranspiration is the main output component of the mass balance and is critical for a correct description of the hydrologic processes during interstorm periods. In this work we calibrate and study the performance of the Kristensen and Jensen model in a semiarid rangeland environment in southwest Spain. For this, a full soil water atmosphere model was used to describe the water fluxes in a column of soil. The model describes variably saturated water flow in the soil using Richards' equation and the van Genuchten soil retention curves. The Kristensen and Jensen model is used to calculate direct evaporation and the water uptake by grass cover. Seven parameters are simultaneously calibrated. Two are for the van Genuchten retention curve and three for the Kristensen and Jensen model. Hydraulic conductivity is assumed to decay exponentially with depth. The decay exponent and the hydraulic conductivity at zero depth are the two remaining parameters to be calibrated. Given the large set of free parameters involved, the calibration set up involves two sources of information: soil moisture measurements at four different depths in the soil column and an auxiliary simple linear model relating maximum daily temperatures and average soil moisture; and two sources of prior information: field capacity measured on soil cores and the maximum dry weight biomass when the soil is fully covered by grass. A global search method (SCE-UA) is used to locate the global minimum in the allowed parameter error space and a local search gradient based algorithm (Levenberg-Marquardt) is used to refine the search from the global solution and to obtain information in the vicinity of the minima. The results indicate that correct parameters of the soil retention curve are more critical for a proper simulation of the water uptake than are Kristensen and Jensen model parameters. Furthermore the calibrated van Genuchten parameters differ from the suggested values for silt-loam soils and they force a steeper effective retention curve and effective field capacities values that are lower than those measured in cores.
DE: 1818 Evapotranspiration
DE: 1839 Hydrologic scaling
DE: 1866 Soil moisture
DE: 1875 Vadose zone
DE: 3333 Model calibration (1846)
SC: Hydrology [H]
MN: 2007 Fall Meeting