I'm afraid I haven't understand you throughly.
You say: Firstly the theme (topic), then the rheme (comment), but in the following phrases I see it in the contrary.
"Strong rain (theme) was the cause of flood... (rheme)"
"Напомним, что причиной наводнений и оползней в Бразилии стали сильные тропические ливни".

"Australia (theme) was victim of flood (theme)"
"Ещё одной страной, пострадавшей от наводнений в январе стала Австралия."

"The flood (theme) is considered the more destructive ...(rheme)"
"До сих пор самым разрушительным за всю историю штата считалось наводнение 1974 года".

I think I haven't understood your commentaries appropriately. Isn't it?