Event Based Risk : Something that has not happened and may not happen at all. If it happens then it will impact everything and it is INDEPENDENT OF WHAT AND HOW WE DO THINGS.
Non - Event Based Risk: Two types, Variability risk & Ambiguity risk.
Variability Risk : We did everything perfectly we could. Still, Uncertainty about some characteristics of planned events exists. Something will happen for sure, range of the outcome is also known, What exactly it might be, is uncertain.
Ambiguity Risk : Risk arising because of lack of knowledge, i.e; we ourselves keep a possibility for risk since we dont know things.