There should be an easy way to get damages per event and region_id.

There are many ways to implement this, but all of them come with a price on calculation and/or memory. From a discussion on Slack a vague plan emerged to

• introduce an additional method in Impact that provides this kind of aggregation
• introduce an additional argument in the ImpactCalc.impact method that indicates how/whether to persist the aggregation result within the Impact object.