Sensitivity analysis of a land surface scheme using multicriteria methods

Abstract

Attempts to model surface-atmosphere interactions with greater physical realism have resulted in complex land surface schemes (LSS) with large numbers of parameters. A companion paper describes a multicriteria calibration procedure for extracting plot-scale estimates of the preferred ranges of these parameters from the various observational data sets that are now available. A complementary procedure is presented in this paper that provides an objective determination of the multicriteria sensitivity of the modeled variables to the parameters, thereby allowing the number of calibration parameters and hence the computational effort to be reduced. Two case studies are reported for the BATS model using data sets of typical quality but very different location and climatological regime (ARM-CART and Tucson). The sensitivity results were found to be consistent with the physical properties of the different environments, thereby supporting the reasonableness of the model formulation. Further, when the insensitive parameters are omitted from the calibration process, there is little degradation in the quality of the model description and little change in the preferred range of the remaining parameters. 1. Introduction and Scope This paper is one of three that discuss the usefulness of multicriteria methods for the evaluation and improvement of land surface schemes (LSS). A companion paper (Gupta et al., this issue) shows how multicriteria methods can be used to improve the estimates of LSS parameters by simultaneously constraining the model to measurements of several observed system responses such as heat fluxes, ground temperature, and surface soil moisture. This paper develops that study by intro- ducing a robust multicriteria approach to parameter sensitivity analysis for LSS models and by showing how the methodology provides a way to reduce the dimensionality of the parameter estimation problem. In both papers, the methodology is illus- trated using the Biosphere-Atmosphere Transfer Scheme (BATS) (Dickinson et al., 1993) and two data sets, one from the ARM-CART grassland site and the other from a semiarid site in the Sonoran Desert, Arizona. A third paper (in preparation) will discuss the power and applicability of multicriteria meth- ods for the evaluation of model performance and for model intercomparison.