Is there a good reason to not merge these together? Or would it be easier to find questions about risks if these questions all shared a common tag?
I'd put risk and risk management in the same bucket of being general categories of which schedule risk is a sub-set. There's not a huge volume of any particular one.
I'd vote for merging them all into risk management. Strikes me as more project management oriented and thus more likely to be a match for a search on the topic (from Google or within PMSE).