Death waves!

Are you watching your pollutions levels? Make sure you aren't pulling water from polluted areas and make sure that people aren't living near factories, crematoriums, incinerators, power plants, etc...

Also look at your health map and see if you can find the problem areas.

I had pollution creep into my water intakes. It wasn't even obvious...just a tiny brown color and started noticing a wave of death. After tweaking around I noticed the issue and promptly fixed. Interestingly it took a few years to eventually remedy.

That has to do with the fact that from time to time, a lot of your seniors will die in the same period.

It needs some tweak cause in big cities it will become impossible to deal with those waves.

Well, part of this problem could arise when you zone in big blocks at a time. Everytime you zone a lot at the same time (for example when paused), a new wave of households spawns. Al lot of these households start their life-cycle at the same time, thus approximately ending them around the same time (if all of them recieve the same services). So a lot die at the same time, and new households move in, restarting the cycle.

Haha. I had this very same problem, and posted a thread with the very same title (apparently in the "wrong" category). I reckon it stems from burst zoning and the inability to deal with the deaths when they come (all pretty much at the same time), which in turn makes the problem resonate with itself and become worse with each cycle.

Burst influx > synchronized deaths (population loss) > mass abandonment (further population loss) > new compensatory influx bigger than the previous once things calm down, restarting the cycle and escalating the magnitude of the problem.

I solved it by chasing people out of the city in between the spikes (maxed the taxes ). It calmed the whole thing down, so unless it comes back, it's fine now. You just need to spread those deaths out over time. I've been running close to 20 years after the last serious spike. There's some up and down, but nothing like before, and it's not escalating.

That said, I believe the game needs some safeguards against this, such as not having all the people die at the exact same age (or very nearly), and not have them all be the same age when they move in. Just distributing the parameter values a bit should prevent this sort of thing from happening.