The bombs were supposedly detonated in the air to maximize damage from the shockwave, the primary effect of the blast. Immediate radiation exposure is a secondary effect that subsided when the reaction terminates, while fallout is tertiary effect that can be heavily influenced by weather patterns and decontamination efforts after the fact.

Both cities have been rebuilt and are doing fairly well, while the corpus of somatic effects of radiation are derived from the study of those populations following the bombings

Chernobyl is also an interesting case in that many of the local residents did not leave and many remain to this day. I think thyroid cancers saw a statistical increase in the surrounding area but nothing exceptionally dramatic. It is a tourist attraction for some as the radiation levels are just above background.

Joint government studies on Fukushima have revealed that evacuation had a harsher effect on at risk (read:elderly) populations given a higher mortality rate as compared to cohorts to weren’t evacuated. Which is to say nothing of long term effects that will be evaluated as time goes along.

$0.02

Yep