Underground housing, underground businesses, etc. Would that be better for the environment + possibly save on energy costs? Also possibly safer in certain scenarios like tornadoes etc.
Potential issues that immediately come to mind are ventilation, earthquakes, and flooding. But it’s not like underground dwellings/basements/etc. aren’t a thing, so maybe those issues have been addressed in ways I’m not familiar with.
The tradeoff for resilience in emergencies is that the if the ventilation fails hard enough, everyone who can’t get out suffocates. Flooding, as you guessed, is also a serious probelm. Everything that can flood a basement now floods a living space.
Heat and AC are normally going to cost less, but the cost of construction, maintenance, and modification of the structure are way higher and generally kinda dangerous. Not worth it.