Number 06/Failure & fragility/Resources
The Depletion Depth
The quantity
The fraction of a stored buffer consumed before extraction or service costs begin to rise sharply. It is the fraction that is genuinely usable rather than nominally present.
01Why it matters
It converts a stock estimate into a service estimate, and the two differ by an order of magnitude in aquifers, reservoirs and inventories.
02Expected value
Between one fifth and one half for most physical buffers, because costs rise non-linearly as the buffer empties.
03How it would be measured
Plot unit cost against cumulative extraction and locate the inflection.
04What would refute it
A linear cost curve would make the fraction one and remove the distinction.