System Dynamics Simulation Slobodan P. Simonovic

Introduction Water resources systems are too complex to be understood by intuition, compromise and superficial debate pollution energy shortages engineering unemployment No one person can be an expert in every field

Introduction So what are we to do? Mind are own business and ignore everything else? No way ‘everything else’ invades our lives ( job loss;.... ) Anticipate Our choice or another’s depends on what is happening in the rest of our society. We do need to understand the world around us, but we can’t possibly become experts in every subject.

Introduction Is there a way out of this trap ? Yes, and its called systems thinking. Still a new subject ( strange for people trained in the traditional way ) most of what has been written about it has been very technical, and difficult.

Introduction I expect: That you will learn to learn new subjects easier and apply basic principles/rules of how systems work to social, political, economic, ecological, and physical systems. You will learn how to make complex problems easier to understand, (solving problems that cross the boundaries between different disciplines ). You will get some suggestions about effective strategies for influencing the world around you, ( identification of “high leverage points” ). You will get some help in developing a comprehensive world view of your own.

What is a system approach? Science approach to learning: take apart and find out what it is made of (division of science into specialties). to extreme known as “reductionism”. something is nothing but the sum of its parts. Example: a comfy house is the same as a pile of building material. The main difference is organization (patterns)

What is a system approach? In 1920 research of patterns began (general systems theory). startling discovery: no matter how different the ingredients of different systems looked, they were all put together according to the same general principles of organization. great impact: development of computers (practical application of “systems analysis” - essential for the management of all business and institutions). two most important conditions: systems theory provides a way of tackling big, messy, real-world problems. systems theory provides a way for average people to get a good, clear picture of how their environment works

System A system is a collection of parts which interact with each other to function as a whole Example: cooling system in a car: radiator, fan, water pump, thermostat, hoses and clamps.

System Systems can be part of a larger system (subsystems) particle atom molecule brain cell brain nervous system individual local community state nation world civilization world ecosystem planet earth solar system galaxy universe

System Why not just have larger and larger atoms instead of building molecules up? answer is stability maximum size of animals (whale - food) social organizations (5 can work as a team, 5000 hardly)

System Dynamics A rigorous method of system description, which facilitates feedback analysis via a simulation model of the effects of alternative system structure and control policies on system behavior Management science – MIT (Forester)

System Dynamics System Dynamics simulation approach relies on understanding complex inter- relationships existing between different elements within a system. This is achieved by developing a model that can simulate and quantify the behavior of the system. Simulation of the model over time is considered essential to understand the dynamics of the system.

System Dynamics Steps: Understanding of the system and its boundaries; Identification of the key variables; Representation of the physical processes or variables through mathematical relationships; Mapping the structure of the model; and Simulating the model for understanding its behavior.

System Dynamics Well suited for representing mental models that have been developed using systems thinking paradigm. Build around a progression of structures.

System Dynamics A system is defined as a collection of elements which continually interact over time to form a unified whole. The underlying pattern of interactions between the elements of a system is called the structure of the system. The term dynamics refers to change over time.

System Dynamics Definitions A dynamic system is thus a system in which the variables interact to stimulate changes over time. System Dynamics is a methodology used to understand how systems change over time. The way in which the elements or variables composing a system vary over time is referred to as the behavior of the system.

System Dynamics Definitions A system’s structure determines the system’s behavior. System Dynamics links the behavior of a system to its underlying structure. System Dynamics can be used to analyze how the structure of a system can lead to the behavior which the system exhibits.