Modelling Catchment-Scale Responses to Climate Change - Climate Change Impacts on Freshwater Ecosystems - page 237

to produce climate change scenarios at the catchment scale. A credible methodology
for converting the predictions of GCMs to the spatial scale required (known as
downscaling) and of generating the resultant 'weather' needed by the models (e.g.
daily precipitation and temperature) must be available. Secondly, models must be
developed which connect catchment climates to variables that can be measured
and which are features of interest in aquatic systems, such as water flows, water
quality or the abundance of aquatic organisms. These models may involve detailed
representations of catchment structure and function and their interactions with
climate, or they may be more empirical. All models need to be tested to determine
whether they represent observed data adequately, normally in an iterative cycle
of testing and revision. Once a model is performing satisfactorily as judged by its
ability to reproduce observations and conform to notions of how a catchment
functions, a set of changed climates can be used to drive the model to produce a
set of changed response variables. Thus, models can potentially provide an
estimate of the effects of the changed climate on nitrate concentrations or fish
biodiversity, for instance. Potential changes in catchment structure and function
due to climate change must be considered during this process (e.g. the alteration
of vegetation types in the catchment). Finally, the influence of changes in
catchment management (e.g. novel crops or agricultural practices) can be assessed.
These might, for instance, be due to changed climates, socio-economic factors or
adaptive responses of catchment managers attempting to mitigate climate change
effects.
This chapter outlines how this approach was used within Euro-limpacs, illustrates
how the modelling process was applied in a range of case studies and describes how
a consistent modelling approach for assessing flow and water quality across Europe
was developed. The science of modelling was taken further by chaining models to
simulate the response of flow and nitrogen at the catchment scale. Models that
incorporate ecological effects have been developed for lakes, but for rivers these
remain a research goal owing to the dynamic, complex nature of the river
environment (Chapra 1997). The main focus of integrated modelling in the Euro-
limpacs project was the development of catchment-scale models of flow and water
quality. The applications described are a small sample of those undertaken. As the
plethora of abbreviations and acronyms used in modelling work can rapidly become
confusing, Table 10.1 is provided for explanation and reference.
The Euro-limpacs modelling strategy
Developing an integrated toolkit of models for catchment analysis and assessment
has been central to the Euro-limpacs project, based on six key questions: (i) Can
the impacts of climate change, land-use change and pollution be evaluated using
modelling? (ii) How can models be used to assess likely effects of climate change
on freshwater systems? (iii) Can models simulate the spatial/temporal variation in
pollutant behaviour in freshwater systems? (iv) Can the uncertainty associated
with these models be quantified? (v) Can socio-economic scenarios be incorporated
into modelling assessments of climate change effects? (vi) How can models be
best used to assist the management of surface waters influenced by climate