[computerphage]

Why is it relative humidity that matters here instead of absolute humidity?

[bob1029]

Relative humidity is an easier unit to work with because it auto scales with temperature.

[OJFord]

I think GP knows that and it's exactly their point: why do you need slightly less water to stop mould growth as the temperature slightly drops? (If anything, one might expect the opposite anecdotally - it's e.g. hot and humid bathrooms that are particularly prone.)