In terms of single-incident, I believe hydro takes the lead due to the Banqiao Dam failure (floods over 12,000 square kilometers killing ~30k directly then ~100k more from water contamination and famine). But even that's still dwarfed by the more gradual impact of climate change on the planet from fossil fuels.

Dam failures absolutely destroy vast areas and can contaminate them with oil and gasoline by flooding settlements. In fact hydroelectric power has killed a surprising amount of people.

> Accidents in other energy sources don't render 1,000 square miles of land uninhabitable.

https://en.wikipedia.org/wiki/2021_Texas_power_crisis

  The grid came within minutes of overloading and shutting down completely, which would have required a slow and costly black start.

That would have rendered 268,596 square miles uninhabitable, at least for several weeks plus recovery time.

How about https://www.ferc.gov/media/winter-storm-elliott-report-inqui... ?