A great natural disaster or cataclysm (large-scale natural upheaval such as earthquakes, floods, volcanic eruptions).
その小説は天変地異を背景にして人間の生き方を問う。
That novel uses a cataclysm as its backdrop to question how people live.
昔の人は天変地異を神の怒りや前兆と考えたことが多い。
In the past, people often thought great natural disasters were signs of divine anger or omens.
天変地異の予測は難しく、日々の備えが重要だ。
Predicting cataclysms is difficult, so daily preparedness is important.