Nature & Environment

### Become an OU student

Understanding the environment: Complexity and chaos

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

# Activity 5E: Developing your own system dynamics diagram

In this activity the aim is to practice system dynamics diagramming as a means to visualise the interaction between stocks and rates as part of a systemic understanding of a complex situation.

## Activity 6

For this activity, I would like you to focus on a few components which you will need to choose from the sign graph you developed in Activity 4A. This can be an entirely paper-based exercise – you do not have to use NetLogo (or a graphics software package) to draw your system dynamics diagram. To construct the diagram proceed as follows:

• i. Sketch out a system dynamics diagram with one of your chosen components as the ‘central’ stock.
• ii. Name the rates that cause an increase and a decrease in the stock level.
• iii. Now, identify at least two other stocks which influence the input rate and/or the output rate.
• iv. Finally, identify (by drawing links) and describe (verbally and/or mathematically) the relationships between these stocks. Are there any positive and negative feedback loops?

Now for the reality check. For at least the central stock, collect trend data. This does not necessarily have to be numerical – graphs will be fine. There are several excellent sources of global and national trend data online, including the World Resources Institute’s EarthTrends [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] . You may encounter significant challenges for this part of the activity – the measurement of trend data is highly dependent on the definition attributed to a particular stock or rate. For example, some of the data you will come across will only represent a subset of what you are looking for – limited to a particular geographical region or sub-topic of your particular area of interest. You will therefore need to develop more precise definitions for your stocks and/or accept less accurate data.

You should choose at least a 50-year time span for your stock(s). Obviously, the greater the time span, the more you can infer about the relationship between the stocks. If you cannot find all the required data you can ‘estimate’ some values, as long as the variations over time make sense. Use this data to explore the dynamic changes in the stock(s) over the time period you have selected by roughly sketching one or more graphs. Now answer the following questions:

1. What trend do you notice in your stock(s)?
2. Is there constant or exponential growth or decrease at some stage in the dynamics?
3. Is there a levelling off occurring?
4. Can you detect oscillations in the stock(s)?
5. What does this tell you about the feedback loops in operation?