# Systems Thinking - Unit 3

Systems Thinking Modeling a System A simple example of a dynamic system a bathtub The balance between the inflow through the faucet and the outflow through the drain determines how much water accumulates in the tub. Is this system open or closed? Examples in the Earth System Inflow (runoff, precipitation)

Outflow (stream outlet) Reservoir (pond) https://en.wikipedia.org/wiki/Alpine_Lakes_Wilderness#/media/File:Lila_Lake_26527.JPG Examples in the Earth System Inflow (snowfall) Outflow (melting, icebergs)

Reservoir (glacier) http://cdn.antarcticglaciers.org/wp-content/uploads/2012/08/fs20093046_fig03.pn Examples in the Earth System Respiration and Decomposition Atmospheric CO Photosynthesis 2 760 Gton(C) 60 Gton(C)/year

60 Gton(C)/year Outflow Reservoir (atmosphere) Outflow Examples in society Inflow (entrance) Outflow (exit)

Reservoir (parking lot) https://en.wikipedia.org/wiki/ Parking_lot#/media/ File:P3030027ParkingLot_wb.jp g Examples in society \$

\$ Inflow (income) Outflow (spending) Reservoir (Bank account) https://openclipart.org/detail/231056/bank Why use a systems model?

Systems diagrams are useful for showing relationships in a system: Bathtub Systems models are useful for quantifying relationships in a system, and allowing system behavior to be explored experimentally: 10 liters 1 liter/minute

1 liter/minute Systems model of the bathtub STELLA is a software package that allows the user to build icon-based dynamical systems models The goal is to take the systems diagram of a bathtub and simulate in a STELLA model A STELLA model of the bathtub system includes a reservoir for the bathtub, and two flows that represent the faucet and drain Inflow

Reservoir Outflow Unit 3 Bathtub Model Model: icon-based representation of the system Equation: mathematical representation of the system STELLA does the calculations for us Output: graph of the system model output

as it runs - in this case, the change in the water in bathtub with time Systems modeling The bathtub model is simple enough that we could just do the calculation of flows and reservoir size with each time step by hand BUT, when a system is more complicated, a systems model becomes necessary to keep track of everything For example, below is a systems model for the Earths energy balance (i.e., inflow of energy from the Sun, the Earth reservoir of energy, and outflow of energy back to space)

Inflow Reservoir Outflow

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