日本の雨季はいつ始まりますか。

Japan

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

rainy season

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

to need; to want

indicates two contrasting actions; indicates possessive (often found in place names and compound words)

to begin; to start; to commence; to happen (again); to begin (anew); to date (from); to originate (in)

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way