What is Stock and Flow Diagrams?

A stock and flow diagram is a modeling tool from system dynamics that separates a system into stocks, the accumulations that can be measured at any point in time such as inventory, water in a reservoir, or trust in a team, and flows, the rates that increase or decrease those stocks such as hiring, evaporation, or broken promises.

Mapping stocks and flows makes it possible to see why systems often respond to change more slowly, or more explosively, than intuition suggests, since a stock only changes as fast as its flows allow. This is the same logic used to model everything from population growth to climate change to a company's cash position.