Calculate buckets (e.g. for weather warnings)

[jimknopf6782]

When there are weather warnings (e.g., intense heat or extreme heat), I want to subtract a value (e.g., 1 or 2) from the bucket if it's above 0.

The reason is when it's hot after heavy rain, it takes too long to reach my settings for watering.
My watering starts from a certain negative value and reset the bucket to 0. When it rains, the bucket becomes positive.

I want to do this with an automation, it executes in both cases, but the bucket value does not change.

Am I making a mistake? It should work, right? Does anyone have an idea?