I think "threat" is something that come from outside that will bring negative impact to existing activities, while "risk" comes from internal side with predictable impact. In some cases threat can be switched into oppotunity while risk become challenges to motivate the people involved.

Instead of doing a math, explain the effect with human expression is most helpfull to clients / team - be prepary a real activity and tactics to deal with theat or risk with the goal could be switch the threat as opp or move the risk into motivation.