Analysing the Human-Ocean System in the Context of Tourism

Models are simplified representations of a part of reality that we are concerned with. A mental model is a model that is constructed and simulated in our mind. When it comes to complex systems, our mental models are usually inadequate. The process of modelling and simulation makes us reason more precisely about systems. System Dynamics modelling is a tool to help construct, simulate, and communicate mental models.

Identify key variables and the causal relationships between them. Find feedback loops and mark them. See next panel for more.

Identify stocks and flows from the Causal Loop Diagram. Use software such as Vensim or Stella Architect to create a System Dynamics model showing stocks, flows and variables, and add equations to capture the dynamics. The tourism model diagram from Stella Architect is shown on the left.

The model is a logical representation of the system. Vensim or Stella Architect software can be used to run the model and generate data. See the model diagram we used below.

Model variables and structure can be changed and then re-simulated, in order to test the effectiveness of plans to improve the system. The results can be surprising!

- Draw a Causal Loop Diagram (CLD), starting with the variables you are interested in (eg Tourists).
- Draw arrows from one variable to another, where the first variable influences the second variable.
- For each arrow, work out whether an increase in the first variable causes an increase in the second variable, or a decrease. Mark each arrow accordinglingly.
- Find 'Circles of Causality' - starting at one variable, can you follow arrows to get back to where you started? If so, you have found a Feedback Loop.
- If the arrows in a circle are all increasing, then you have found a Positive Feedback Loop.
- If an odd number of arrows in a circle is decreasing, then you have found a Negative Feedback Loop (this is a 'rule of thumb' that usually works!).

A Causal Loop Diagram (CLD) often looks like this, with increasing arrows marked '+', decreasing arrows '-', positive feedback loops 'R' (for 'Reinforcing'), and negative feedback loops 'B' (for 'Balancing').