ABSTRACT
Modeling is central to many hydrologic decisions, both in analysis and in design. Decisions in hydrologic engineering often require the development of a new model or the use of an existing model. When developing a new model, the response of the model should closely mimic the response of the real-world system being modeled. Before using an existing model, the modeler should verify that the model is appropriate for solving the type of problem being addressed. When a modeler uses an existing model developed by someone else, the modeler should be sure that he or she completely understands the way that the model responds to the input. In all of these cases, the modeler should understand the model being used. Sensitivity analysis is a modeling tool that is essential to the proper use of a model because it enables the model user to understand the importance of variables and the effects of errors in inputs on computed outputs.
