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The general approach in these models is to use rainfall and evaporation data as inputs. Stream flow is produced as a model output, often as the sum of quick flow and slow flow components (Figure 1). If , as illustrated in Figure 1 (Note that slow flow includes lateral subsurface throughflow - also known as interflow - as well as baseflow, but for the purposes of the SRG it is lumped together with baseflow). If evaporation data is not available, temperature may be used as an input in some models (e.g. IHACRES Classic). The complexity of the models varies considerably from four parameter models (e.g. GR4J) to models with a large number of conceptual stores and parameters (e.g. the Sacramento model).
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Choosing the right model
Choosing which of the above models is the most appropriate to use for a given application may not necessarily be straightforward. Consider the following when choosing a rainfall runoff model:
- What models do you and other people in your organisation have experience with;
- Have any rainfall runoff models worked well for your catchment in the past;
- What type of catchment are you modelling? (urban, forested, mixed land use);
- What data do you have available? You need to parameterise any models you choose; and
- Do you have any information on previous rainfall runoff model calibrations? If calibrated models already exist, you can re-use the models and parameter sets.
These approaches might also be useful:
- Run a range of different models and determine which ones work best; and
- Consider using different models or parameters, in different sub-catchments or functional units. What works best in one functional unit may not work well in another. For example, different models may be useful where sub-catchments/FUs have different soil types (different soil water holding capacity) or different proportions of urban areas (large differences in impervious runoff).
- Use an ensemble of models
More information on model choice, and rainfall-runoff modelling as a whole, is available from a number of sources including:
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including eWater's Guidelines for water management modelling and the supporting Guidelines for Rainfall-Runoff Modelling (accessible via the link for Guidelines for water management modelling).
Reference
Welsh, W.D., Vaze, J., Dutta, D., Rassam, D., Rahman, J.M., Jolly, I.D., Wallbrink, P., Podger, GM., Bethune, M., Hardy, M.J., Teng, J., Lerat, J. (2013) An integrated modelling framework for regulated river systems. Environmental Modelling & Software, 39: 81-102.
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