I. Identify the problem
There is an oscillation with the food supply which hinders the number of nomads from increasing.
II. Reference Mode
Shown in the figure above that since there will be oscillations with regard to the food that the nomads will eat, then the population will also incur the same behavior as the nomad food supply. The food supply limits the growth of the nomad population, thus a continuous oscillation happens.
III. Causal Loop Diagram
The proponents made a causal loop diagram to have a background of the situation. It is shown in the figure below.
The first loop to be discussed is the relationship between the variables population of nomad, mature cattle, water supply, and nomad death rate. The loop made by these variables is a positive feedback loop. Population of nomad has a negative effect on the population of cattle since they are the main source of food, the cattle on the other hand has a negative relationship with water supply, the water supply has a negative effect with the death rate and the death rate has a negative effect on nomad population. The next loop will be consisting of the mature cattle, cattle food supply, and cattle death rate. The loop is a negative feedback loop and could be the cause of oscillation with respect to the nomad population.
IV. Stock Flow Diagram
The stock flow diagram as shown above is the expanded form of the causal loop diagram. This is for the deeper understanding of what the causal loop diagram is trying to say. First of all is that the proponents made a delay on the food supply this to make the situation close to reality so that the food supply will not increase and decrease rapidly. Other variables added are for the birth rate and death rate of nomads, these are just constants that are multiplied to the rates for the inflow and outflow of nomad population. Other variables are also expanded such as the water supply where an outflow rate is added since water supply is a level variable.
V. Simulation results
After running the model, the proponents came across this graph shown below.
It is seen that there is an oscillation with respect to the food supply and the population of nomad as hypothesized. Although the water supply oscillated during the first 30 periods, it is seen that the oscillation of food supply still continued, this is due to that the grazing spots took time before it ran out. Taking note that the grazing spots is where the cattle eat their food. It can be realized
that the cattle does not rely on water that much since it is in scarcity compared to the grazing spots where they can move from one spot to another.
VI. Sensitivity Analysis
Increasing or decreasing the rate of water does not affect the food supply and nomad population, the graph still remains the same. The same goes if grazing spots will increase rapidly. The trade off between the food supply of nomads and its population will still continue to oscillate and will find equilibrium after a long period of time.
VII. Learnings
Each part of the stock flow diagram must be thought of really well. A mistake in any of the variables may give you bad results
.
Case 4
Tragedy of the Sahel
I. Identify the problem
There is an oscillation with the food supply which hinders the number of nomads from increasing.
II. Reference Mode
Shown in the figure above that since there will be oscillations with regard to the food that the nomads will eat, then the population will also incur the same behavior as the nomad food supply. The food supply limits the growth of the nomad population, thus a continuous oscillation happens.
III. Causal Loop Diagram
The proponents made a causal loop diagram to have a background of the situation. It is shown in the figure below.
The first loop to be discussed is the relationship between the variables population of nomad, mature cattle, water supply, and nomad death rate. The loop made by these variables is a positive feedback loop. Population of nomad has a negative effect on the population of cattle since they are the main source of food, the cattle on the other hand has a negative relationship with water supply, the water supply has a negative effect with the death rate and the death rate has a negative effect on nomad population. The next loop will be consisting of the mature cattle, cattle food supply, and cattle death rate. The loop is a negative feedback loop and could be the cause of oscillation with respect to the nomad population.
IV. Stock Flow Diagram
The stock flow diagram as shown above is the expanded form of the causal loop diagram. This is for the deeper understanding of what the causal loop diagram is trying to say. First of all is that the proponents made a delay on the food supply this to make the situation close to reality so that the food supply will not increase and decrease rapidly. Other variables added are for the birth rate and death rate of nomads, these are just constants that are multiplied to the rates for the inflow and outflow of nomad population. Other variables are also expanded such as the water supply where an outflow rate is added since water supply is a level variable.
V. Simulation results
After running the model, the proponents came across this graph shown below.
It is seen that there is an oscillation with respect to the food supply and the population of nomad as hypothesized. Although the water supply oscillated during the first 30 periods, it is seen that the oscillation of food supply still continued, this is due to that the grazing spots took time before it ran out. Taking note that the grazing spots is where the cattle eat their food. It can be realized
that the cattle does not rely on water that much since it is in scarcity compared to the grazing spots where they can move from one spot to another.
VI. Sensitivity Analysis
Increasing or decreasing the rate of water does not affect the food supply and nomad population, the graph still remains the same. The same goes if grazing spots will increase rapidly. The trade off between the food supply of nomads and its population will still continue to oscillate and will find equilibrium after a long period of time.
VII. Learnings
Each part of the stock flow diagram must be thought of really well. A mistake in any of the variables may give you bad results
.