1st International Congress on Environmental Modelling and Software - Lugano, Switzerland - June 2002
Keywords
uncertainty analysis, 3d water-quality models, lagoon of venice
Start Date
1-7-2002 12:00 AM
Abstract
This paper presents the application of both local and global sensitivity analysis techniques to anestimation of the uncertainty of the output of a 3D reaction-diffusion ecological model, which describes theseasonal dynamics of dissolved Nitrogen and Phosphorous, and that of the phytoplanktonic andzooplanktonic communities in the lagoon of Venice. Two sources of uncertainty were taken into account andcompared: 1) uncertainty concerning the parameters of the governing equation; 2) uncertainty concerning theforcing functions. The mean annual concentrations of Dissolved Inorganic Nitrogen, DIN, was regarded asmodel output, as the current Italian legislation sets a quality target for Total Dissolved Nitrogen in the lagoonof Venice. Local sensitivity analysis was initially used, so as to rank the parameters and provide an initialestimation of the uncertainty, which is due to an imperfect knowledge of the dynamic of the system. Thisuncertainty was compared with that induced by an imperfect knowledge of the loads of Nitrogen, whichrepresent the main forcing functions. On the basis of the results of the local analysis, the most importantparameters and loads were then taken as the sources of uncertainty, in an attempt to assess their relativecontribution. The global uncertainty and sensitivity analyses were carried out by means of a sampling-basedMonte Carlo method. The results of the subsequent input-output regression analysis suggest that the variancein model output could be partitioned among the sources of uncertainty in accordance with a linear model.Based on this model, 87.8% is due to the uncertainty in the parameters which specify the dynamics ofphytoplankton and zooplankton only % of the variance in DIN mean annual concentration is accounted for bythe uncertainties in the three main source, while.
A comparison between the uncertainties in model parameters and in forcing functions: its application to a 3D water quality model.
This paper presents the application of both local and global sensitivity analysis techniques to anestimation of the uncertainty of the output of a 3D reaction-diffusion ecological model, which describes theseasonal dynamics of dissolved Nitrogen and Phosphorous, and that of the phytoplanktonic andzooplanktonic communities in the lagoon of Venice. Two sources of uncertainty were taken into account andcompared: 1) uncertainty concerning the parameters of the governing equation; 2) uncertainty concerning theforcing functions. The mean annual concentrations of Dissolved Inorganic Nitrogen, DIN, was regarded asmodel output, as the current Italian legislation sets a quality target for Total Dissolved Nitrogen in the lagoonof Venice. Local sensitivity analysis was initially used, so as to rank the parameters and provide an initialestimation of the uncertainty, which is due to an imperfect knowledge of the dynamic of the system. Thisuncertainty was compared with that induced by an imperfect knowledge of the loads of Nitrogen, whichrepresent the main forcing functions. On the basis of the results of the local analysis, the most importantparameters and loads were then taken as the sources of uncertainty, in an attempt to assess their relativecontribution. The global uncertainty and sensitivity analyses were carried out by means of a sampling-basedMonte Carlo method. The results of the subsequent input-output regression analysis suggest that the variancein model output could be partitioned among the sources of uncertainty in accordance with a linear model.Based on this model, 87.8% is due to the uncertainty in the parameters which specify the dynamics ofphytoplankton and zooplankton only % of the variance in DIN mean annual concentration is accounted for bythe uncertainties in the three main source, while.
