There are different shittos what to do in the southern hemisphere (and differences between South America and Australia). However, many agree that once the chachamin set the zman for Bavel we don’t change
it. Many seem to say that regions in the Southern Hemisphere say Morid Hatal all year, Vsein Brocha all year but if rain is needed, say Vsayn Tal Umatar in Shema Koleinu.
See BETZEL HACHACHMAH Chelek Vav Siman Pay hay (85)
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Minchas Yitzchak chelek Vav Siman kuf Ayin Alef
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