While some residents took a wait-and-see attitude, others prepared for the major flood.
Literal
Some [possessive-の] residents [subject-が] wait-and-see [possessive-の] attitude [object-を] take [while-一方で] other [possessive-の] people [topic-は] great-flood [for-に] prepared.
様子見 ('wait-and-see') — literally 'watching the situation' — is a common compound for cautious inaction. ~一方で ('on the other hand, while') contrasts the two groups. 備える ('to prepare for, to be equipped against') takes に for the thing prepared against. The sentence models a clean contrastive structure common in news and essays.