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Quantification of Model Output Uncertainty Due to Watershed Size

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  022227,  2002 ASAE Annual Meeting . (doi: 10.13031/2013.10430) @2002
Authors:   Vijay Garg, Indrajeet Chaubey, Brian Haggard
Keywords:   AGNPS, calibration, rainfall-runoff modeling, scale, hydrologic modeling, parameter uncertainty, watershed, validation

A hydrologic/water quality model must be calibrated before used for predicting watershed response. Often the measured data from the watershed where the models are applied may not be available. Under this condition, models are calibrated using data from a different watershed having similar land use, soil, and hydrologic conditions. However, if the watershed used for model calibration is not same as the watershed where the model is applied for hydrologic/water quality predictions, the difference in watershed characteristics may induce error in model output. The objective of this study was to quantify the error in model predictions due to watershed size. Agricultural Non-point Source (AGNPS) model was used to quantify the model errors using measured data from watersheds of varying sizes from the Little Washita Basin in Oklahoma. The study indicates that a large uncertainty in the model outputs results with the change of watershed size.

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