More formal/written than near-synonym 急剧 jíjù (same pinyin, slightly different second char). Both mean 'sharp/sudden change'; 急遽 leans literary, 急剧 is the everyday choice in news and reports.
mistakes
Don't confuse with the homophone 急剧. Editorial style guides usually prefer 急剧 in journalism — 急遽 reads as bookish.
