[adelie]

it's a common expression here in the US, at least! unsure about the UK.

[eru]

It would be exceedingly funny, if the expression had become idiomatic in the US, _because_ of the book.

(However, it might have come to US English from Spanish which is pretty close to Portuguese and thus ultimately from the same source as the book?)

[anthk]

Spanish has "llover a cántaros" too.