My model is on global population and its impact on the availability of natural resources. The stocks in my system include food availability, soil resources and water resource availability. One question I believe my model can address is, what are the connections between food availability, soil resources and water resource availability; or in other words, are these stocks influenced equally by variables?  I hope to show a direct correlation between all three of these stocks. Food availability as stated in The Impact of Population Growth on Food Supplies and the Environment stated that, “The continued production of an adequate food supply is directly dependent on ample fertile land, fresh water, energy, plus the maintenance of biodiversity.” As population continues to grow so will the inputs to natural resources including water, fertilizer, and the need to have more available land.  What is more astonishing is that if these natural resources are never completely tapped dry, on a per capita perspective availability these resources will decline on astronomical levels since it has to be split amongst people (Pimental et al, 1996).

The flows in my system include food production,drought, water pollution, and greenhouse gases. I picked drought as a flow since it directly impacts the level of water available. Take for instance in California, the five year drought has caused scarcity and triggered state-wide executive orders to conserve water (California Department of Water Resources, 2017). Drought and water pollution can be affected by the number of people living in a country, which is why I picked these elements as flows. Furthermore food production, water pollution and greenhouse gases have strong influences on the availability of natural resources.

I picked mortality rates, birth rates, water scarcity, and industrial development as my variables. Since birth rates and mortality rates vary depending on the country I picked these as variables on my system since population growth is influenced by these variables.   Impact of Population Growth describes how the U. S. is already being affected by population growth, as stated here, “In populous industrial nations such as the United States, most economies of scale are already being exploited; we are on the diminishing returns part of most of the important curves.”

I have decided to change “developed countries” and undeveloped countries” as stocks to variables since these factors actually act more like variables. One question I hope to address with my model is how developed countries can  reduce their impact on resources? Furthermore, Population growth rate does depend on whether a country is developed versus undeveloped, so a country's level of economic development is more of a variable. I have decided to change food production from a stock to a flow, since it seems to be more of a flow that might affect the level of a stock of available food. I have also changed water scarcity from a stock to a variable because it actually affects the flow of water into an overall stock of fresh drinking water