Dynamic stock modelling
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Dynamic stock modelling (DSM) is a new development in material flow accounting and explicitly considers the role of in-use stocks in past, present, and future material use.
In-use stocks of buildings, infrastructure, and (durable) products play several important roles in social metabolism:[1]
- They supply physical services such as transportation or shelter to people.
- They are 'capital containers' and 'resource repositories' representing large accumulations of fixed capital and materials; for example, steel and concrete in buildings.
- They are 'dynamics determiners'; their lifetime determines replacement flows and when new technologies can penetrate the market.
- They are 'wealth watchers' and can serve as an indicator of the amount of services utilized within a given socio-economic system.
- They are 'consumption couplers' because their technical properties determine the energy and material throughput required to operate them.
- They are 'city shapers' as the location and density of buildings determines transport patterns and other parameters of the urban fabric.
Dynamic stock modelling (DSM) explicitly considers these different roles of in-use stocks. DSM has a long tradition in modelling population and fixed capital; over the last twenty years, applications for product and material stocks have been developed.[2] Age-cohort-based models, state-of-the-art in DSM, are of a descriptive nature: Each age-cohort is assigned an expected lifetime and the cohort's use phase ends when its lifetime elapses. At any given point in time, in-use stocks are composed of different age-cohorts, each with its specific material content and energy efficiency.[3][4] In DSM, the assumed total stock size is determined by exogenously specified parameters such as population and per capita service level[5] and the age-cohort lifetime model can be used to adjust the inflows into and the outflows from stocks.