Absolutely ignore this if it’s over-explained and you don’t care, but I thought it topical considering your username here, but do you know the RAVEN hack? I used to use it back when I taught ESL.

Remember: ‘affect’ verb. ‘Effect’ noun.

So when it’s the verb, the ‘action’ word of the sentence, it’s ‘affect’, like: ‘it really affected me’ And when it’s a noun in the sentence, it’s ‘effect’, like: ‘the after-effects were really bad’ or ‘the special effects in this movie are great’

So in your sentences: ‘things happening in and effecting Melbourne’ ‘Happening’ and ‘effecting’ are the verb forms here, so it should be ‘affecting’

‘…around things that effect Victoria’ Again, ‘effect’ is the verb here, so it should be ‘affect’ If it was something like ‘the effects of the flooding on rural Victoria’, then ‘effects’ is correct, because it’s a noun.