## Parameter Uncertainty

In order to perform a stochastic simulation range and distribution of
each model parameter must be defined. REBEKA2 allows choosing uniform,
normal, lognormal and triangle distributions. Ranges can be defined as
absolute or relative. The above screenshot shows a part of the model
parameter table that allows defining the parameter range and
distribution.

It is currently not possible to consider correlations between
parameters although they exist (e.g. between reservoir time constant
and contributing area and reservoir time constant). It is very
difficult to take parameter correlation into account because either the
correlation is unknown or not well defined. The program RANDSAMP of the
library UNCSIM which is used
to generate the parameter samples allows accounting for parameter
correlation (Reichert, 2001) in principle but it is not implemented in
REBEKA2. It will be probably considered in a future version.

### REFERENCES

Reichert P. (2001). UNCSIM - A
program package for uncertainty analysis and Bayesian inference: User
Manual. Dübendorf, Switzerland, EAWAG: 36.