Long term, the projections are for more frequent and violent weather events ranging from floods to droughts. Too much water in some locations and not enough water in others. FEMA has a Disaster Reservist Program I've written about before, but its membership has been drastically reduced in recent years based on administrative fiat from the Craig Fugate era at FEMA.
To be able to surge people in the last few months, most "normal disasters" that had already been declared were put "on pause" and people shifted to the triple threats of the three hurricane events. While FEMA has dedicated staff, teams (Incident Management Teams) that are dedicated to managing disasters, those are nowhere sufficient to deal with the size and scope of what we've seen recently. I can tell you that the spouses of FEMA's employees who are "supposed to be working in a fixed office environment" are saying, "This isn't what I signed up for!"
What is the right number of new hires that is needed? I really don't know — but, I do know their staffing levels for full-time employees (FTE) is not what is needed for today and for the future.
It will likely take the Government Accountability Office and perhaps the FEMA inspector general to identify and justify the need going forward. It would be problematic for Brock Long, FEMA administrator, to be the one asking for more staff in an era of "smaller government" and lower taxes.