Is there any difference between "Conceptual Models" and "Simplified Conceptual Models" in hydrology?
I mean if it is just a matter of simplification or these two expressions are used for two Different type of models with different characteristics and applications?
The additional explanation is that:
"Simplified Conceptual Models" are the Same as "0-term" or 0D (zero dimensional) models
You already know the answer. The name is based on the number of dimensions or parameters considered for conceptual models.
In my opininon, 0D and 1D can be considered as simplified conceptual model and others can be just referred as "Conceptual Models"
simplified conceptual models have very few parameters and are far from representing the reality of a hydrological region compared to conceptual models.
I also agree with the suggestions by Negin Binesh and Sheikh Mohammad.
Both 0D,ID far away from the reality region considered simplified while others are conceptual.
Agree all.
Conceptual models focus on identifying and working with the major drivers and parameters of a physical process (e.g. groundwater flow or contaminant transport) in an area or region. They can be valuable in obtaining order-of-magnitude estimates and bracketing the likely values of an endpoint of interest (e.g., groundwater flux or a contaminant breakthru curve for a certain cross-section in the domain); and thus help in design and development of a more detailed model, and/or help guide fieldwork data collection that can most effectively help constrain the parameter space and model results. Also, such models can often be compared with analytical solutions or approximations for the problem of interest, including dynamical scaling approximations of dominant regimes for various processes across values of key parameters or parameter combinations.
Previous responders have done a good job answering your question. The key element in those answers is: "how well does a model represent reality?"
We have the same problem with terms like "physical" models and "physically based" models.
We're unable to create models which represent reality, regardless of the number of dimensions because the values of the parameters change discontinuously both in time and space. Scale is also important. Additionally, water states and movement in the environment are governed by physics which operates at the atomic scale, further compounding the problem. Out of necessity, then, we average, simplify or "conceptualize" the reality (physics).
As a result we resort to models whose value is judged by "fit for purpose". For example, a unit hydrograph model, is extremely simple, has low dimensionality and averages many aspects of the reality of catchment response. Yet it is often used because it is judged fit for purpose.
Even further, we are generally unable to completely define the inputs and outputs. It is not possible to measure the amount of rainfall at all time and space scales and it is similarly hard to measure outflow.
One result of this complexity is that we use descriptors such as "conceptual", "simplified conceptual", "physical", and "physically based" and the we get hung up on the definition of these terms.
We should be less hung up on those terms and concentrate more on fitness for purpose.
More directly addressing your question--there are in general no precise criteria for distinguishing between a 'Conceptual Model' and a 'Simplified Conceptual Model' (in agreement with Bonnin's answer above). If presenting the evolution of conceptual model A to conceptual model B, you might name model A the Simplified Conceptual Model and model B the Conceptual Model. Often conceptual models are used for identifying and understanding the dominant drivers and physical processes in a domain of interest, as contrasted with more detailed models that may be directed toward obtaining the most accurate possible numerical estimates of the independent variable(s) or their derivitives (e.g. groundwater heads, head gradients and water fluxes) or of the parameters (e.g. the spatial distribution of permeability).
I forgot to mention that often a numerical model that may be quite detailed is referred to as a 'Conceptual Model' before it is calibrated. After calibration is performed on this conceptual model, the model is then referred to as the 'Calibrated Model'. If furthermore the model is validated, the model may be referred to as the 'Validated Model', or the 'Validated Calibrated Model'.
In my more than three decades of involvement in hydrologic and hydraulic modeling, I have never heard the term 'simplified conceptual model'. But I have seen models classified or described as conceptual, physically based, deterministic, stochastic, etc. etc.
A common problem in hydrology is that many terms are loosely used without first defining them, which then gives rise to a lot of confusion. This does not happen in physics or mathematics. Hydrologists should try not to use terms that are not well defined.
Ferdous Ahmed, in his excellent comment above says "Hydrologists should try not to use terms that are not well defined." I would add that if they do so, they should define or add a reference to the definition. This would go some way towards avoiding "a lot of confusion".
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