Workshop: Modeling Non-Renewable Resources Dynamics

Dr. Bellam Sreenivasulu’s recent workshop about modeling the depletion of non-renewable resources was intended to enable participants to understand the problem holistically through a systems approach. First, learned to construct causal loop diagrams (feedback loops) by applying systems thinking concepts, and then learned to develop stock and flow diagrams as models for simulations to study how a system structure generates the behavior of overshoot and collapse of non-renewable resources.

Dr. Bellam Sreenivasulu led a discussion on System Dynamics modeling with a focus on non-renewable resources. He defined a system as a group of interacting, interconnected, and interdependent elements, which can be tangible or intangible, and can be classified into subsystems based on their boundaries. Sreenivas emphasized that a system is more than the sum of its parts due to emerging behaviors. He also explained the concept of systems thinking, which involves understanding the interconnections and interdependencies among variables, and highlighted the importance of identifying feedback loops. Sreenivas suggested developing systems thinking skills by understanding the dynamic behavior of a system over time using tools such as behavior over time graphs (BOTGs). He also discussed the dynamics of systems, explaining that their behaviors are often nonlinear due to feedback loops and can manifest as exponential growth or decay, goal-seeking, oscillations, overshooting and collapsing, or oscillations like an S shape. Sreenivas stressed that understanding the system structure behind these behaviors is crucial for predicting future patterns.

Model Components: Feedback Loops, Causal Interactions, Stocks, and Flows

Sreenivas explained the concept of feedback loops, emphasizing the importance of understanding causal interactions between variables. He elaborated on the positive and negative influences between two variables, demonstrating how an increase in one variable can lead to an increase or decrease in another. Sreenivas also discussed the concept of link polarity, which determines the direction of the causal link. He further explained the reinforcing feedback loop, which increases in a positive direction, and the balancing feedback loop, which decreases in a negative direction. Sreenivas used examples such as population growth and stress levels to illustrate these feedback loops.

Sreenivas discussed the concept of stocks and flows in causal loop diagrams. He defined a stock as something in the system that accumulates or decreases over time, while a flow is the rate at which a stock changes. He illustrated this with examples such as water levels, blood sugar levels, and vehicle sales. Sreenivas explained the principles of accumulation in stock and flow diagrams, emphasizing that the behavior of the stock is determined by inflows and outflows. He presented a stock and flow diagram for modeling and stressed the usefulness of understanding System Dynamics using two stocks and other variables.

Petroleum Wells System and Population Interactions

Sreenivas discussed the petroleum wells system and the extraction process, highlighting that petroleum wells are non-renewable resources with no inflow and only outflow as reserves decrease. He explained that the extraction rate is influenced by various factors and the depletion of reserves leads to a decrease in the number of petroleum wells. Sreenivas also discussed the causal loop diagram of a population system, focusing on interactions between different age groups and feedback loops. He emphasized the importance of systems thinking, the conversion of a causal diagram into a corresponding stock and flow diagram for systems modeling, and identified stocks, flows, and flow rates.

Petroleum Reserves Modeling Discussion

Sreenivas discussed modeling petroleum reserves extraction wells, focusing on the effects of reservation. He also explained the concept of maximum extraction per well and its unit, emphasizing that the unit of maximum extraction per well is barrels per year. Sreenivas connected the normal closing fraction and the drilling fraction to the closing and drilling wells respectively.

He also discussed the dynamic behavior of petroleum reserves and wells over a period of 25 years, highlighting their overshooting and collapsing trends. Sreenivas also shared a model to help beginner system thinkers understand how non-renewable resources deplete over time.

Modeling Practice in Vensim

Sreenivas provided a tutorial on converting a casual loop diagram into a stock and flow diagram. Participants were asked to watch a video on drawing a causal loop diagram and practice using the Vensim software.

Sreenivas presented the Vensim software, explaining its features and functionalities. He demonstrated the process of constructing a stock and incorporating flows within the model using the example of petroleum wells. Sreenivas also explained how to create causal links, adjust line thickness and link polarity, and indicate the direction of the loop. He further clarified how to depict reinforcing and balancing feedback loops and how to mentally visualize the invisible connections between variables.

Sreenivas provided guidance on the construction and saving of a model, stressing the importance of setting accurate time limits and time steps for precise simulation results. Sreenivas then initiated a hands-on session and guided participants on how to work with the model, emphasizing the importance of understanding and using the provided equations.

Sreenivas provided a detailed explanation on how to use data and lookup functions to generate a graph, highlighting the impacts of payroll resource and petroleum reserves on drilling fraction. Questions about data input and software capabilities were addressed, with Sreenivas confirming the software could generate a report listing all relationships depicted in the graph. Towards the end of the meeting, Sreenivas demonstrated how to use the model menu and check units, emphasizing the importance of using provided documents and data.

He demonstrated how to set equations, highlight variables, and settle units for petroleum reserves and wells. He further explained how to document the initial value and units and how to set constants like the drilling fraction and normal closing fraction. Sreenivas stressed that stock and flow variables have different types, including auxiliary variables, constants, and parameters. Toward the end, Sreenivas discussed the use of a lookup function in modeling.

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Download Model and Supporting Materials from the Workshop

Download the Software

This workshop involved modeling in Vensim PLE, the free version of the modeling software provided by Ventana Systems. Download here: https://vensim.com/free-downloads/

Pre-Work Tasks

Before attending the workshop, participants were asked to complete the PRE-WORK TASKS to ensure a productive learning experience:

1. Watch the introductory segment (up to 10 minutes) of the video on ‘drawing causal loop diagrams (CLDs) in Vensim’ to familiarize yourself with the basics of CLD creation in Vensim. Access the video here: Vensim Causal Loop Diagramming Video.
2. Practice drawing CLDs by replicating the example shown in the video. Once comfortable, save your version of the CLD in the ‘.mdl’ format with your name as the filename.
3. Learn about constructing simple Stock and Flow Models in Vensim by watching the relevant video. This will provide foundational knowledge in creating stock and flow diagrams (SFD). Access the video here: Building a Simple Vensim Model.

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