Adventure ideas for Flooded Post-Apocalypse

[Yora]

I've been thinking recently about post-apocalyptic settings and how three quarters of them seem to be scorching deserts and the remaining quarter frozen waves. It's cool, but already been explored a thousand times.

I got an idea for a post-apocalyptic campaign in which an asteroid impact in antarctica delivered or released frozen mutagenic fungus spores. The fungus spread massively with no predators or competitors in the ice-free impact crater, causing an accelerating thawing process and releasing more spores into the wind to spread all around the world. Most people who inhaled the spores died from lung infection or nerve disorders, and many more died from famine as the rising sea sank most major cities with their ports and industry, and a lot of important farmland beneath the water. Some people have eveloped a limited resistancs to the fungus spores that allows them to survive the contamination that is now everywhere around the world, but can still get sick and die if inhaling thick clouds of them. Some of them are getting affected by more extreme mutations.
Less reflective ice and growing seas means more water surface to evaporate moisture into the warming atmosphere, so storms get bigger and more common and dump larger amounts of rain. When dry winds pick up large clouds of spores and then mix with rain clouds, they result in toxic red rain that people really don't want to get on their skin, their clothes, and their food. And all the nuclear plants, chemical plants, and landfils that sunk beneath the water have turned the Baltic Sea into toxic sewage.

As a local, I think north-central Europe could be an interesting setting. At 90m sea level rise, there would only be a few small islands left of Denmark and Northern Germany. To the south, the Harz would have turned into an archipelago, and to the north Southern Sweden is a large peninsula. Further east there would be a large island that was northern Poland, and another major island that was Lithuania and bits of southern Latvia. Right at the center of it would be Bornholm, which is not only in a seemingly random location, but also weirdly high and still mostly above water. Maybe it's the last remains of the Kingdom of Denmark.

I think nautical post-apocalypse has been done only once, and famously terrible. Concentrating on the new coasts of Germany, Poland, and Sweden and the new coastal island chains could be an interesting setting. Even with a relatively large map, if most of it is water, the amount of land wouldn't be that huge, and if you can sail ships across open water with good wind, going from central Germany to Sweden by boat could be faster that walking a much shorter distance through wooded hills. It would still be a relatively compact setting.
Maybe the fungus grows slower when it's really wet, so the coasts are better places for people to survive? Or something else happened on the mainland that makes people stick close to the sea.

Do you have any idea for what kind of adventures could happen in such a setting? Or what larger events a campaign could be centered around?
With red rain covering the land in spores, river water might not be safe to drink, so you could have the same water shortage adventures as in desert worlds. One really cool suggestion I got was that before the major sea ports were all drowned, people packed ships full with supplies to take them out to sea for safety. Once the people died for whatever reason, the ships get stranded on the coast many years later and might still be full of valuable scavenge. Or they are pirate lairs or crawling with mutants. I could see some Norwegian or Scotish oil drillers still keeping an oil rig running in the North Sea and it being one of the very few sources of petroleum, which they sell for everything they need.

[Pauly]

Some ideas, more or less at random:
1) The rising water and heat levels turns the Europa archipelago into a tropical climate. The mountainous areas (Alps, Tyrol, etc) however become like the Andean altiplano as all the rain falls at lower altitudes. The mountainous areas get their water from spring thaws melting the ice on mountains. Which gives you a mix of jungle settings and semi-desert settings.
2) Take inspiration from pirate settings as islands devolve into self government with the collapse of centralized communications.
3) the spores cause humans to evolve/devolve into reptilian lizardmen, with the people at the low altitudes most exposed getting the full dose and those from higher
altitudes and latitudes being protected by the cold. Bases with enough power to run air conditioning such as the oil wells you suggested could also be protected. This also gives a reason for people to adopt the masks/robes/goggles uniform prevalent in post apocalyptic settings.
If you accept this premise then the spores could cause weird mutations in the animal kingdom too, leading to dinosaur like “monsters”.
4) Nuclear subs
5) Vikings.
6) Diving to recover stuff will be a big deal. Some proper decompression rules would make it more fun.

[Yora]

Nuclear Sub Vikings. :smallcool:

[Grod_The_Giant]

Mad Max: Fury Road, but with inexplicably spikey speedboats instead of cars.

[hifidelity2]

Look at the book series

Sunken City Capers
Book 1 - The Solid-State Shuffle
by Jeffrey A. Ballard

As that has something that you might find useful. The flooding is not as dramatic (IIRC) as yours, and not caused by alien spores, but does give a flavour

[Pauly]

Building on the spores => mutations idea. Modern epigenetics suggest that a lot of what used to be called “junk DNA” is basically evolution saying “I’ll stash that away, I might need it one day” and given the right trigger the gene will activate.

If the spores have visited earth previously, causing one mass extinction event and their eradication caused by a subsequent mass extinction event, then the mutations are a genetic response to the stimuli of the red spores. I’m a fan of going with scales and tails as the most outward sign of mutation, but I wouldn’t go all the way back to cold blooded/egg laying.

As a fun aside it also justifies birds evolving back into non-avian dinosaur types.

What this allows is for an overarching plot where the unmutated populations want to find out how ti eradicate the spores. However the mutated population’s scientists figure out that they will become extinct if the spores are eradicated. Kind of an “I am legend” kind of set up. Humanity is split in 2 camps, with only 1 camp able to be viable in the long term.

[Mechalich]

So, actually, a maritime-based post-apocalyptic setting sent in Scandinavia has been done: the Shattered Sea trilogy by Joe Abercrombie.

However there's a fundamental problem in blending maritime settings and the tropes of post-apocalyptic storytelling, which is that maritime activities require a fairly high level of civilization to be sustainable. You need multiple settlements with a food surplus to start building ships and conducting long distance see voyages. So if you're doing maritime adventures, your post-apocalyptic society has to be well along into the recovery phase.

[Eldan]

I mean, they don't have to be large ships. The Polynesians did pretty well sailing over the Pacific without an industrial base, I'm sure you can handle the European archipelago with longboats.

You could have ancient dangers rising from the deep. Chemical spills, coal ash, oil tanks, old metal mines that flood and suddenly kill off all marine life for many kilometers around. I'm sure the Ruhrpott flooding would be quite unpleasant.

(I wouldn't focus too much on the fungus spores and mutation, or you're just getting Degenesis with a higher sea level instead of an ice age.)

[Yora]

For reference, this is the map I am working with.

http://spriggans-den.com/wp-content/uploads/2022/09/floodmap2.png

That's Denmark, Northern Germany and Poland, and Southern Sweden. With sea level rising over months or years, people who didn't die from disease or starvation would have known that sail boats might become very useful in the future, and they had all the boats in Denmark, Hamburg, Kiel, Lübeck, Rostock, Szczecin, and Malmö to pick from and make stashes of spare parts. The distance from Germany to Sweden would be 400km, which a boat could well make in two days.
I think people traveling around in 10m or 20m ships would be pretty plausible.

And yes, we would also have to deal with all the industrial waste and landfills from these places floating in the water. Since the Baltic Sea is the drainage basin for much of northern and eastern Europe, it's always been flowing out into the North Sea. Which is why the water has fairly low salinity. I think that might continue to be the case even without Denmark funneling the water into a narrow channel. So perhaps the waste from Hamburg, Kiel, and Copenhagen would be flushed out into the Atlantik. There's still all the sludge from the Eastern Baltic, but what can you do? :smallwink:

I noticed that pretty much all major cities in the region will be completely sunken, even such local metropolises like Uelzen and Soltau. But they wouldn't be terribly deep.
How long does the rubber in air hoses and diving masks last? Never seen post-apocalyptic scavenging in diving gear before. Would that be plausible or too far fetched?

As a side note, gas masks would make more sense in this scenario than most, because you could catch fungus spores with just particle filters and the masks would protect you even once the chemical neutralizing material has expired.


As a fun aside it also justifies birds evolving back into non-avian dinosaur types.
Mutated sea gulls. Everyone will hate that.
I love it! :smallamused:

[Eldan]

Done a bit of work with various rubber hoses, including maintenance. Recommended lifetime is 3-5 years for natural rubber, up to 10 for synthetic materials. But I've seen some that last quite a bit longer than that, 20 years is well possible. Still, they get brittle. Bit of googling gives me similar answers: hoses in car motors are recommended to be replaced after ten years at the lastest, 5 years for washing machines and other kitchen equipment.

That's under fairly stable conditions. If this was the post apocalypse and everything was decades old, I wouldn't trust it.

Decent picture: this is a five year old hose from a car, pretty thick material, too:
https://www.autosiliconehoses.com/media/blog/brittlehose.png

That said, you can totally ignore it. Petrol doesn't last more than a few months, either, and yet there's post apocalypses with cars all over, still.

As for maps, I'd totally go with the Netherlands just still being on the map, totally unchanged by the apocalypse, but I'd also mostly play it as a joke. Still, the Netherlands as the technological empire that threatens everyone from the west could work.

[Eldan]

Oh, addendum. If the water over the larger cities isn't too deep, and people still can make large amounts of metal, you might consider salvaging operations with diving bells. Those need pretty large ships and counterweights, though.

Really old school:
https://editorial01.shutterstock.com/wm-preview-1500/6044593bc/e6ea3a4b/Shutterstock_6044593bc.jpg

[awa]

You are not writing a scientific journal but designing an rpg setting, I would recommend ignoring any science that does not fit with your theme. Some science is good depending on your players but dont let it get in the way of a good game.

Worry more about how the setting feels than exactly how it works, your players will get more out of that the minutia of the settings science. Not everything needs to be hard scifi.

To the main topic
1) a late game problem could be some group who found a preserved cache of advanced weapons and are trying to conquer the region.

2) a bunker that was intended to protect the rich and powerful but due to a malfunction killed every one, it should have lots of undisturbed supplies. Recently uncovered its a race to acquire it. (maybe guarded by robots?)

3) zombies cant go wrong with zombies

[Yora]

I find settings always more interesting when they take realism as far as it goes and only make up fantastical stuff when it becomes really neccessary to work.
Limitations are where interesting new solutions are created that give settings a new and unique character. If you just ignore all limitations and do things the way they are typically done in fiction, you end up with something that looks pretty generic and everyone's seen a dozen times before.

When the main threat in the air are particles, leaky gas masks don't bother me.
Bicycle tires are made out of rubber, but they are really simple and there isn't enough cycling-punk, so I go with that as well.
But when it comes to diving, there is lots of rubber parts and just a single one not working can kill you. Because the impact of rubber decay is so big in that case, I feel more hesitant to letting it slide.

Regarding fuel, the region has been growing fuel ethanol crops in some amounts for a good while. While not necessary for a setting, having farms that specifically produce fuel is the kind of interesting result that comes from trying to stretch realism as far as it goes. There's also many oil rigs in the North Sea and there could be a Norwegian faction that keeps one running and has its own oil tanker to ship fuel to buyers. Another thing that sounds cool and happens when you start thinking about limitations.

[Eldan]

And that's taken right out of Waterworld, too! The villains, after all, had an oil tanker they were using to fuel their vehicles. (When I saw Waterworld, I must have been about 10 years old and I thought it was incredibly cool. I always liked the sea, ships and big sea monsters.)

[Amidus Drexel]

On the note of farming fuel, what are most people doing for food? Are they exclusively eating fish and shellfish? Have any species of livestock animal survived the apocalypse? What kinds of edible plants are still around? Does their fungus-modified biology allow them to eat anything unusual?

Possible food-related adventures:

There's an old-fashioned (non-apocalypse-related) blight that's destroyed a town's food source, and the adventurers are sent off to find something to eat.
Investigating some cow rustlers leads to a larger conspiracy (or a hidden stockpile of weapons).
A newly-discovered source of food creates political instability in a community of survivors between those who seek to share it and those who seek to control it.



You are not writing a scientific journal but designing an rpg setting, I would recommend ignoring any science that does not fit with your theme. Some science is good depending on your players but dont let it get in the way of a good game.

Worry more about how the setting feels than exactly how it works, your players will get more out of that the minutia of the settings science. Not everything needs to be hard scifi.


I basically auto-subscribe to Yora's worldbuilding-idea threads because of the neat settings and discussions about the little details. For some of us, that's part of the fun!

[Palanan]

Originally Posted by Eldan
You could have ancient dangers rising from the deep. Chemical spills, coal ash, oil tanks, old metal mines that flood and suddenly kill off all marine life for many kilometers around.

This will be a worldwide issue, to the point that it’s easier to ask what could possibly survive anywhere in the ocean.

Not only industrial waste from seaports, coastal refineries, navy bases and manufacturing complexes, but also the concentrated toxins stored in every Wal-Mart and Home Depot, which will be released into coastal waters and circulated into every ocean basin in a matter of years.

Looking at this map (https://i.redd.it/lp4ei8dyv5o11.jpg), you can see that the Black and Caspian Seas will effectively merge into a single epicontinental sea, and large regions of a certain environmentally insensitive country to everyone’s east will be entirely flooded, adding to the chemical hell the oceans will become.


Originally Posted by Eldan
If the water over the larger cities isn't too deep, and people still can make large amounts of metal, you might consider salvaging operations with diving bells.

Indeed, but freediving is another option. Some pearl divers routinely went 50-100’ down, which might be an option for the more lightly drowned regions.

That said, given the highly toxic nature of the oceans, freediving scavengers might have an even lower life expectancy than from their occupation alone.


Originally Posted by Yora
There's also many oil rigs in the North Sea and there could be a Norwegian faction that keeps one running….

The question here is how long an oil rig can operate without the industrial base that designed it. Also, oil rigs aren’t refineries, so the oil will need to be processed somehow. Refineries are usually on the coastlines.

And speaking of energy production, what about all those offshore wind pylons? Depending how tall they are, some of them might have enough clearance to keep functioning—and if sea level rise was slow enough, there might have been time for someone to reroute the cables for easier access.


Originally Posted by Yora
Nuclear Sub Vikings.

Again, the question here is how long a boomer can stay operational when its home base is gone. This basic overview (https://www.csp.navy.mil/SUBPAC-Commands/Submarines/Ballistic-Missile-Submarines/) suggests a 2:1 ratio for cruising time vs. maintenance, but that requires a functioning homeport with thousands of workers and an entire military-industrial complex behind them. If there aren’t facilities for maintenance then these subs might not last very long.

This also raises the question of radioactivity, not only from the boomer’s reactor and warheads but from civilian nuclear plants around the world. If they’re not shut down safely—and it’s doubtful they would be—then there could be hundreds of reactors cooking off in addition to everything else.

[Yora]

Yeah, there will be plenty of radioactive pits of molten corium around the world. But I'm not sure how much fumes they give off and how much of the heavy metals can be dissolved by water running over it during heavy rain.
I am also not sure how big the impact of chemical spills into the sea will be, given the amount of water in the oceans.

I absolutely would rely on boiled rainwater for drinking, but I am not sure how dead the seas would be. Though my notes folder is labled "Murky Waters". :smallwink:

As for food, potatoes and cabbage have been staple crops in the region for a long time. As well as cattle and pig farming. The elevated areas in Northern Germany also have been traditional sheep pastures, which is some nice local color to add.
Though I am not sure how well pigs would actually work, given that they have very similar food requirements to humans. They can be used to turn food that is edible but people don't want to eat into a different type of food, but it's still a net loss in food overall.
I also can see a revival of sugar beets for sweets and apples as the main resource to make alcohol. :smallbiggrin:

I've been thinking about how one would make gunpowder. Since black powder is lower power than smokeless powder, it should work with modern rifles (though perhaps requiring manual cycling) and you can reuse the brass cartridge from old ammunition. I wasn't sure where you'd get pottasium nitrate for black powder that hasn't already been mined in this part of the world, but turns out the traditional source is just bird poop. Since we're only looking at a few thousand rifles in active circulation, an annual harvesting of the local mutant seagull breeding grounds should provide a sufficient supply. :smallbiggrin:
(No clue where you would get the sulfur from, but eh...)

[thorr-kan]

Not quite what you are envisioning, but if you want weird, post-apocalyptic flooding, you could do worse than Superhero Necromancer Press's "The Rainy City" series of zines. It's a rainy, flooded city surrounded by endless ocean. When the waters rise and you flee the world's end, you end up there eventually. Everybody ends up there eventually.

For earth, there's flooding map at: https://www.floodmap.net/?z=2&e=45. Set it to 4500m and look at Tibet/China. Plateau of Leng anyone? Anyone?

For impact events, there is: https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/, the Earth Impact Effects Program.

If want to limit yourself to old-fashion nuclear weapons, there is: https://nuclearsecrecy.com/nukemap/, the NUKEMAP.

And finally, just for historical interest: https://www.measuringworth.com/, How Much Was What Worth When?

[Quertus]

Let me open with the question I’m sure my players would ask first: are there any gun factories - or, more importantly, bullet production sites - in your unflooded map? (Plus, of course, the requisite resources?)

Given rubber decomposition issues, I’ll ask about facilities and resources to produce rubber, too.

And… even if those areas are “too hazardous” for humanity, could your lizard mutants operate them?

Are there any… important psychological changes in the lizard mutants? Could mixed societies exist? Could there be PC lizard mutants, or an “all lizard” game? Or are they inherently genocidal towards all pink-skins, despite being sentient beings?

With things flooding slowly, it seems that an awful lot could be salvaged ahead of time. I would think that “industry” would be a fairly high priority to relocate, but I could be mistaken.

With things flooding slowly, I expect that most of humanity would flee inland, not fritter around on the moving target that is the coastline.

Can oceanic oil rigs acclimate to a 90m sea level differential? If not, how long would it take to refit them?

With the toxic waste and red rains, I imagine sea food would be mutated, toxic, and dead. So, 10-year-old rotting radioactive toxic mercurial mutant fish not sounding very appealing, and decades old canned goods not sounding much better, what do people actually eat? Albatross?

If there’s fuel farms, I’m guessing “real farms” answers the food question, but… 1) at what point is there enough “plenty” that “fuel” takes priority over “food”; 2) can this produce be processed into “fuel”; 3) can vehicles operate exclusively off plant fuel?

What nations would geographically (ie, ignoring the red rain, or the lack of global markets) be largely unaffected by the flooding?

Those are my initial reasons to question whether your world will look the way you imagine.

Is your objective to ask, “what world do I get by introducing this apocalypse”, or “what apocalypse do I need to introduce to get this world”?

[Palanan]

Originally Posted by Yora
But I'm not sure how much fumes they give off and how much of the heavy metals can be dissolved by water running over it during heavy rain.

Water which drains into the rivers and thence to the seas, thus increasing the radioactivity and heavy-metal toxicity of the world’s oceans.


Originally Posted by Yora
I am also not sure how big the impact of chemical spills into the sea will be, given the amount of water in the oceans.

The impact is already immense in the present day, but it’s not always easy for any one person to see, and the entities responsible for individual incidents often do their best to prevent any coverage. There are massive oil spills that take place on the seafloor around drilling rigs that escape public notice because no one’s there to film them.

And that’s just today’s impacts. The next time you’re in a large home-improvement store (maybe OBI or Bauhaus?) take a look at the pest-control aisle. If it’s anything like stores in the US, it’ll have a floor-to-ceiling stockpile of pesticides, fungicides, baits and poisons, all of them concentrated and toxic.

Multiply that by the tens of thousands of similar stores around the world that are within 90 m of current sea level. “The solution to pollution is dilution” was the catchphrase back in the 1960s, but we’ve learned since then that it simply doesn’t work. Toxins leaching into flooded coastal waters from the US Gulf Coast and Atlantic Seaboard will be drawn into what’s left of the Gulf Stream and brought directly to the North Sea.

This is to say nothing of the pollution leaching from hundreds of thousands, if not millions, of drowned vehicles in the flooded regions, plus countless garages and service bays, bus fleets and depots, railyards and airports, not to mention tens of thousands of gas stations and hundreds of Superfund sites. That’s just in the US, and all of that will be joining the Gulf Stream as well.


Originally Posted by Quertus
With things flooding slowly, I expect that most of humanity would flee inland, not fritter around on the moving target that is the coastline.

This is a very First World perspective. Most of the people affected globally will not be living in First World countries, and many of those people simply won’t have the resources to easily relocate hundreds or thousands of miles inland. And many of them won’t see a need to, simply from an urgent focus on living day-to-day. If they’re surviving on the coastline, they’ll move with the coastline.

.

[Eldan]

And the various german mining areas near the Rhine, which are going to flood. Old coal mines, and the waste from coal plants.

[Quertus]

This is a very First World perspective. Most of the people affected globally will not be living in First World countries, and many of those people simply won’t have the resources to easily relocate hundreds or thousands of miles inland. And many of them won’t see a need to, simply from an urgent focus on living day-to-day. If they’re surviving on the coastline, they’ll move with the coastline.

.

Uh, pardon my stupidity (said in all seriousness), but I kinda thought a) the initial “we’ll safeguard and stockpile boats” was a rather “first world” response; b) most of the countries on the map of “where this will take place” were “first world”; c) “just keep moving for high(er) ground” was a mindset that could exist independent of country of origin; d) “survival on the (moving) coastline” is dubious because “the glowing fish be dead” and there ain’t no farms (what ain’t already claimed) for the vagrant coastal wanderers to survive off of.

My confusion was with the premise that, after flooding that wiped out the majority of supporting ship faring infrastructure (docks, shipyards, you name it), most of humanity would now be concentrated near the new coast.

[Yora]

A pure sea level rise disaster would probably look quite different from the typical nuclear apocalypse scenarios in the genre. Which is why I came up with a deadly airborne infection carried by the wind around the whole world to kill off most of the population quickly.

In a pure flood scenario, I think the original number of drowning deaths would be fairly low. When the water is rising by a meter per week, people will run. I think the real killer would be starvation. Not only is all the coastal farmland gone, pretty much every major port will be gone too. And probably the vast majority of major cities and much of the rail infrastructure. Similarly, most heavy industry sites are close to the transportation infrastructure, and what remains will be cut off from many of their vital suppliers.
As a mostly uneducated rough estimate, I think the global food production would drop by 90%, and possibly a lot more than that. I don't know how much organized salvage and relocation would be possible to get done in that situation.
If you had 10 meters in 100 years, the situation would of course be very different than 100 meters in two years.

[Yora]

A new question to all of you regarding settlements and wilderness.

Using real elevation maps of Denmark and northern Germany and setting the new sea level to where I think the islands look nice (at +80m), I ended up with six main islands and a bunch smaller ones with a total area of about 6,000 km². Roughly comparable to the Balearic Islands or half the size of Northern Ireland. Since I want to make the sizes of settlements and factions be plausible with the amount of wilderness between them, I did a quick calculation applying a population density like Sweden, Bhutan, or New Guinea, which came out as a total of 120,000 people.

That seems quite a lot.

With 12 factions, that would be 10,000 people on average. Make just a tenth of these fighters, and that would still be quite considerable forces numbering hundreds to a few thousand people. Have settlements with a thousand people on average and there would be 120 of those.
Now Sweden has apopulation of 10 million, but 4 million of those live in the three largest cities alone. I'd guess it's like that in most sparesely populated countries. If we ignore those and apply the population density of the remainder, we'd get something like 70,000 people for those 6,000 km² islands. Still quite a lot.

Ultimately this comes down to a choice of preference. But what are your thoughts on this? Do you think any kind of balance between open wilderness, settlement frequence and sizes, and faction scales has more merits for campaign purposes than others?

[Quertus]

Oh, does “boiling water” actually kill normal “irl” spores? Just curious how obvious (and how prone to failure) this technique should be.


A pure sea level rise disaster would probably look quite different from the typical nuclear apocalypse scenarios in the genre. Which is why I came up with a deadly airborne infection carried by the wind around the whole world to kill off most of the population quickly.

In a pure flood scenario, I think the original number of drowning deaths would be fairly low. When the water is rising by a meter per week, people will run. I think the real killer would be starvation. Not only is all the coastal farmland gone, pretty much every major port will be gone too. And probably the vast majority of major cities and much of the rail infrastructure. Similarly, most heavy industry sites are close to the transportation infrastructure, and what remains will be cut off from many of their vital suppliers.
As a mostly uneducated rough estimate, I think the global food production would drop by 90%, and possibly a lot more than that. I don't know how much organized salvage and relocation would be possible to get done in that situation.
If you had 10 meters in 100 years, the situation would of course be very different than 100 meters in two years.

Are there any places on your map where one couldn’t just walk from the old shore to the new shore (or further), even traveling at the 3e standard “half speed to forage as they go” (whether that represents “pick berries”, “raid abandoned Walmart”, or “kill people and take their stuff”) inside, say, a month?

I don’t think global food production will be hot as hard as you think - at least, not by the flooding alone. But, given that shipping food is likely a thing of the past, what you need to look at IMO is local food production - and this will generally be true of each locale.


A new question to all of you regarding settlements and wilderness.

Using real elevation maps of Denmark and northern Germany and setting the new sea level to where I think the islands look nice (at +80m), I ended up with six main islands and a bunch smaller ones with a total area of about 6,000 km². Roughly comparable to the Balearic Islands or half the size of Northern Ireland. Since I want to make the sizes of settlements and factions be plausible with the amount of wilderness between them, I did a quick calculation applying a population density like Sweden, Bhutan, or New Guinea, which came out as a total of 120,000 people.

That seems quite a lot.

With 12 factions, that would be 10,000 people on average. Make just a tenth of these fighters, and that would still be quite considerable forces numbering hundreds to a few thousand people. Have settlements with a thousand people on average and there would be 120 of those.
Now Sweden has apopulation of 10 million, but 4 million of those live in the three largest cities alone. I'd guess it's like that in most sparesely populated countries. If we ignore those and apply the population density of the remainder, we'd get something like 70,000 people for those 6,000 km² islands. Still quite a lot.

Ultimately this comes down to a choice of preference. But what are your thoughts on this? Do you think any kind of balance between open wilderness, settlement frequence and sizes, and faction scales has more merits for campaign purposes than others?

I guess that depends on just what level of “action hero” the PCs are supposed to be, and how much encounters with masses of NPCs should play out like Mad Max, or Water World.

Personally, IMO, with people thinking in terms of modern population densities, but without modern infrastructure and medicine to back it up? I think that normal, mundane communicable diseases could have wiped the population down to whatever smaller size you prefer, even before the spore related deaths and lizard rat swarms.

Oh, speaking of retaining population: what’s required to make “mandatory” medicines, like… blood pressure meds, or insulin? Is everybody with such a condition likely already dead?

Or, more generally, what will the governments - especially those on the “play area” your map covers - prioritize? Even ignoring failures, what will they try to maintain?

EDIT: if we’re worried about losing rubber hoses and petrol, we’re looking at old-school subsistence farming. So, 90+% of your population needs to be farmers, or something. No “3% of the population feeds the community” any more.

[TeChameleon]

How much of the world map have you looked at for the 80-90m sea level rise, Yora?

Because looking at North America, there would be enormous swathes of farmland completely untouched by the rising seawaters, and a big chunk of the populace wouldn't be particularly disturbed by them either. Yes, you'd lose enormous numbers, but you'd still have (at a very, very rough guesstimate) at least half the population of Canada and the USA unbothered by the waters, including the overwhelming majority of the farmers.

There's also the fact that the Rocky Mountains form a natural barrier to airborne pathogens- Alberta, on the Eastern side of the Rockies, is in the 'rain shadow'. Combine a rich agricultural, protected area with significant reserves of oil and natural gas in that same area, a capital that is well clear of the ocean, and Canada could end up being somewhat less post-apocalyptic than the rest of the world :smalltongue:

[Yora]

If supply of fertilizer and farming equipment breaks down almost completely, there would still be a lot of food that can be produced in such regions. But I would suspect only a fraction of what it is now. Maybe a third, a quarter, or even less. That food would also have to be consumed locally and couldn't be delivered to food importing regions at previous capacities.
99% of all people starving to death seems unlikely. But 80% or even 90% before things find a new equilibrium doesn't seem too far fetched to me.

Which is why I think a plausible global depopulation scenario also needs to have a killer plague on top of that. Then you can cut the world population down to a hundreth or a thousandth.

[Eldan]

In modern times, you really just need air and electrical power to make fertilizer, then you can set up a Haber-Boscch process. That's how almost all nitrogen fertilizer is made. Eventually, you want phosphorus, too, but you can get that from urine.

I'd just ignore the US for this. THeir farmland and much of their industrial base will be basically untouched.

[Quertus]

If supply of fertilizer and farming equipment breaks down almost completely, there would still be a lot of food that can be produced in such regions. But I would suspect only a fraction of what it is now. Maybe a third, a quarter, or even less. That food would also have to be consumed locally and couldn't be delivered to food importing regions at previous capacities.
99% of all people starving to death seems unlikely. But 80% or even 90% before things find a new equilibrium doesn't seem too far fetched to me.

Which is why I think a plausible global depopulation scenario also needs to have a killer plague on top of that. Then you can cut the world population down to a hundreth or a thousandth.

Well, that’s the trick: different areas will be hit differently.

Least affected will be areas that are self-sufficient: they have (for example) oil, refineries, and plastic & tire factories, all connected by roads above the flood zone. But anything that they’re dependent upon imports - specifically, imports from across the pond? That’s where they’ll have to adapt, or their systems will fall apart.

On a micro scale, there’s plenty of “farmers” who will starve to death. That is, “specialist” farmers (corn farmers, pig farmers, whatever) might have “food”, but they’ll lack nutritional variety. Without (local) trade, they’ll starve as surely as anyone else.

Truly self-sufficient farms and communities might be nearly unaffected. I can see North America… following the Fallout script, actually: the US and Canada merging, draconic “anti-travel” laws being enforced to conserve oil while ports are desperately rebuilt. I imagine that, even in this state of affairs, like the Ministry at Hogwarts, the US would continue trying to meddle in world affairs as long as possible.

Actually… if I were in charge of this post apocalyptic US, I would “order” (make “food delivery” contingent upon) mass migration from cities to the country, to have “all hands on deck” doing farm work manually, to conserve gas for transporting produce, and for the (army and) navy.

The plague adds a bit of a twist. Are there WHO… um… “bases” on the surviving portion of your map? Because I imagine that “experts on disease” (and corresponding facilities) would be something my players would focus on in this scenario.

Of course, how useful those will be for how long, as society collapses, will vary. Nations that can quickly convert their power grid to wind or similar (or who aren’t dependent upon coastal nuclear reactors or imports for their power in the first place) might keep their WHO powered until the plague makes “power line fixer” (inside joke) a dangerous profession.

Without modern tools, I’m assuming we’d be back to subsistence farming, with 90+% of the population (regardless of how many or how few that is) involved directly in food production (farming, hunting, fishing, transporting, whatever). Which is somewhat independent of “how many of them can fight”. In fact, in a zombie apocalypse scenario (or “mutant animal” scenario or whatever), I imagine that, in most settlements, *most* of the citizens would be combatants. And, with the population shrinking, but the number of guns remaining the same, it would be unwise to assume that any of them are unarmed.

So… hmmm… the “mightiest” nation might well be the one for whom “modern farming” is something that requires them 0 imports, because they can then afford to have the bulk of their citizens doing something other than farming. Such a nation could have a trained army, industry, universities - whatever they chose to do with their 97% “surplus” manpower.

(EDIT: were I in charge of such a “has modern farming” nation/community, reproducing would be job 1 for the survivors.)