Sensitivity analysis using mass flux and concentration

✍ Scribed by Thomas Meixner; Hoshin V. Gupta; Luis A. Bastidas; Roger C. Bales

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 229 KB
• Volume: 13
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/(sici)1099-1085(199910)13:14/15<2233::aid-hyp870>3.0.co;2-5

✦ Synopsis

Sensitivity analysis for hydrochemical models requires consideration of the multivariate nature of watershed response. A robust multiobjective generalized sensitivity analysis (MOGSA) procedure, recently developed at the University of Arizona, was used to fully investigate the single objective parameter sensitivity of the Alpine Hydrochemical Model (AHM). A total of 20000 simulations for a two-year period were conducted for the Emerald Lake watershed in Sequoia National Park, California. For each simulation 21 objective functions were evaluated: they were discharge and both concentration and mass ¯ux for ten chemical species. The MOGSA procedure revealed that only 2000 simulations were necessary to establish the parameters sensitive to mass ¯ux or concentration. We found signi®cant dierences in parameter sensitivity for concentration versus mass ¯ux objective functions. For example, a snowpack elution parameter and a number of hydrologic parameters were sensitive for Cl À concentration, while only the snowpack elution parameter was sensitive for Cl À mass ¯ux. By using mass ¯ux instead of concentration fewer mineral weathering parameters and more soil exchange parameters were sensitive. Mass ¯ux calculations emphasize the spring snowmelt and peak discharge events of the early summer. Our results indicate that using mass instead of concentration permits better identi®cation of the model parameters that most aect stream conditions during peak springtime ¯ows and that some combination of mass ¯ux and concentration objectives should be used in evaluating model performance.