Learn Italian: Più la pioggia è abbondante, meno irrigazione serve. - The more abundant the rain is, the less irrigation is needed.

In English, we use "The more... the less..." to show proportion. In Italian, you never use definite articles before più and meno in these structures. You simply start the clause directly with the comparative words.

Why does serve translate to "is needed" instead of "serves"?

The verb servire is very frequently used to mean "to be necessary" or "to be needed". When used this way, the thing that is needed is the grammatical subject. Therefore, meno irrigazione serve literally means "less irrigation is necessary".

Is meno acting as an adverb or an adjective here?

In the second clause, meno acts as an adjective indicating quantity modifying irrigazione (less irrigation). Unlike most Italian adjectives, meno is invariable, meaning its ending never changes, even when modifying a feminine singular noun like irrigazione.

Could I change the word order and say Più è abbondante la pioggia?

Yes, that is also grammatically correct. However, placing the subject directly after Più or Meno followed by the verb (Più la pioggia è abbondante) is the most common and natural word order for these proportional structures.