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5.7.3 Modelling approaches

In CIS guidance 10 (Rivers and lakes – typology, reference conditions and classification systems,
2003) some remarks are made about modelling approaches:
(20)
When adequate numbers of representative reference sites are not available in a region/type, predictive modelling, using
the data available within a region/type or borrowing data from other similar regions/types, can be used to determine
reference values. One of the advantages of using predictive approaches is that the number of sites needed for reliable
estimates of mean or median and error are usually lower than those needed if spatial approaches are used. This usually
results in fewer sites that need to be sampled, together with lower implementation costs. A second advantage of using
predictive approaches is that the models can often be inverted to examine the likely effects of mitigation measures. It
must be stressed that predictive models only are valid for the ecoregion and water body type for which they are created.

5.7.4 Expert judgement 5.8 Intercalibration

Expert judgement usually consists of a narrative statement Intercalibration is an important way of ensuring consistency
of expected reference condition. Although an expert’s in boundary setting and assessment across all European
opinion may be expressed semi-quantitatively, qualitative Member States. It allows the use of different assessment
articulation is probably most common. Use of expert methodologies but ensures consistency and comparability.
judgment may be warranted in areas where reference sites This is a process undertaken infrequently (at most, once per
are few or absent. WFD planning cycle) but is important to ensure comparability.

One of the strengths of this approach is that it may also 5.8.1 Aim of
be used in combination with other methods. For example,
expert judgment may be used to extrapolate findings from intercalibration
one quality element to another (eg paleo-reconstruction
using fossil diatom remains may be used to infer
invertebrate community composition), or to extrapolate Intercalibration is a component of the Water Framework
dose-response relationships to those expected in Directive for ensuring that every Member State’s ecological
unperturbed sites. quality objectives and assessments of quality against those
objectives are consistent across the EU. This ensures that
Another strength of this approach is that both empirical the High-Good and Good-Moderate status boundaries for
data and opinion can be amalgamated with present-day each biological quality element in each water body category
concepts of ecosystem structure and function. However, relates to the same quality in each Member State, despite
as a number of weaknesses are inherently associated with differences in their biotas and assessment methods. It also
this approach, caution should be exercised when using it ensures that their methods comply with the normative
as the sole means of establishing reference conditions. definitions in the Directive (Annex V, 1.2).
For example, subjectivity, eg the common perception
that it was always better in the past, and bias, eg even Different countries have different biological assessment
sites with low diversity can be representative, may limit its methods because they already had well-established
usefulness. Other drawbacks include the lack of clarity methods before WFD, because of biogeographical
or low degree of transparency in assumptions used to differences in their biotas, and because of differences in the
establish reference and the lack of quantitative measures, environmental pressures as a result of differences in human
eg mean or median values for validation. A further activities. Intercalibration enabled countries to continue to
weakness of this, and many other approaches is that the use and develop their existing methods and avoided the
measure obtained is often static, and hence does not need to develop new methods specifically for the Directive.
include the dynamic, inherent variability often associated Another strength of this approach is that both empirical data
with natural ecosystems (CIS Guidance Nº 10). and opinion can be amalgamated with present-day concepts
of ecosystem structure and function.

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