Environmental Engineering Reference
In-Depth Information
Fig. 2.1 Basic steps of environmental systems analysis and modelling (adapted from M
uller
€
1999)
Although these questions seem to be trivial, they are often not dealt with in a
satisfactory manner in practical modelling applications. However, answering these
questions and documenting the derived conception needs to be done before techni-
cal steps of model development are taken. There are two main reasons for this
requirement: On the one hand, this allows one to find the optimal conception for the
model without forgetting or neglecting basic preconditions, and on the other hand,
the documentation of the respective answers will enable the modeller to return to
his original objectives when he has been lost in the complexity of model improve-
ment. Figure
2.1
further illustrates that model development follows a cyclic pro-
cess: Already with the definition of the data requirements, limitations might
become obvious that make it necessary to change the general outline. The results
of calibration and validation (see below) usually support this
experience
, and
sometimes demand the modeller to go back to the very first steps because some
basic requirements could not be met.
Taking into account these working procedures, two focal strategic items should
be highlighted to avoid an exaggerated application of the cyclic principle:
Models Require a Clear and Precise Specification of the Focus
of Investigation
A clear distinction needs to be made between what is part of the problem and what
is left out of the considerations. This may sound fairly straightforward; however, in
almost any practical situation this decision poses a serious challenge. The web of
ecological interactions is complex. However large the resources for research might
