In reality there's an impact or atmospheric detonation in the ballpark range of that size, maybe one a year or so. Sometimes more. Early warning launch satellites, and nuclear test detection satellites pick them up now and then. In the early days of the satellites, they caused some false positives, until they figured out that the signatures didn't match nuclear detonations, and things like x-rays and gammas were missing.
Luckily most of Earth is covered by water, and despite our population, large stretches of the land surface that's already in the minority are sparsely or completely uninhabited.
