It seems valuable to distinguish between long-standing practices and things that might be called historical "events." For instance, different systems of slavery would be moral catastrophes that were long-standing practices. Wars and genocides might be more like "historical events" (although some happened over rather extended periods of time). 

Some other long-standing practices that seem to qualify, depending on your moral views. 

1. Factory farming
2. Forms of (mass) incarceration (and other systems of state-sanctioned punishment)
3. Certain actions with respect to our environment and non-human life on the planet
4. Mass mistreatment of certain groups of people (e.g. societies that accept rape)

Possible "events" that seem to qualify: 

1. Setting up colonies (many instances, was usually supported by large groups of people, not just by the governments themselves)
2. Some additional categories of events that are always or often moral catastrophes: wars, genocides, any situation in which large groups of people suffered and the world could have helped more than it did (any famine, refugee crises, etc.), democides (e.g. millions of people killed under Stalin in the USSR, even setting Holodomor aside)
3. There are resources like this list of wars and anthropogenic disasters by death toll (this also provides ideas for classification)

I'm a little concerned that attempts at trying to determine what "how often moral catastrophes happen and the scale of suffering they cause" will be highly definition-dependent. E.g. if you lower your bars for criteria # 1 and 2 for what you call a moral catastrophe, you'll get more moral catastrophes. But I personally found thinking about past "moral catastrophes" and the ways in which they were justified in different societies helpful for trying to identify possibly current and future moral catastrophes, so the project does seem quite useful. 

(By the way, another possible resource for this could be the list of references in the paper linked in the post you reference--- although I haven't actually read the paper or the references, only the summary.)

(I made this a comment as it doesn't seem specific enough to be an answer, but I'm not sure that that was the right call.)

Hi folks! Thank you so much for the warm reception this post has received so far. I'm actively trying to improve my EA-aligned research and writing skills, so I would really appreciate any constructive feedback you might be willing to send as a comment or a private message. (Negative feedback is especially appreciated.) If you are worried about wording criticism in a diplomatic way, Linch (my supervisor) has also offered to perform the role of a middleman. 

Of course, we would also appreciate being informed if any of the proposed research ideas actually change your decisions (e.g. if you end up writing a paper or thesis based on an idea listed here). (And I would be really curious to see where that goes.)

On a different note, there are additional posts that I would have linked to this one if I had published later. In particular, the Vignettes Workshop (AI Impacts) , Why EAs researching mainstream topics can be useful (note: Michael and I both work at Rethink Priorities),  this post about a game on animal welfare that just came out (I haven’t tried the game), and this question about the language Matsés and signaling epistemic  certainty .