So much good stuff on geography and physics in such a short time!
More geography considerations:
More concerning than rivers flowing through deserts is how does there manage to be a desert in the first place?
Consider: STerra is like Earth. The sun rises in the East. The (albeit cylinder shaped) planet spins anti-clockwards. Weather systems move West ==to=> East.
Mahrlect, I hadn't thought of that. I guess I just kind of assumed that rain fronts would come from the sea. Rain from the east woudl get stopped by the mountains. Rain from the west would gradually exhaust itself over the land. But I suppose by that logic, the much larger continent West Colassia, especially Fumaya would be bone dry.
SCIENCE!
...needs to explain this.
Real science. Weather fronts endlessly flow toward the East on Earth because of the Coriolis Effect. CE is caused by the spherical shape of Earth. On a cylinder world ...no Coriolis Effect ??
I guess I can go back to Greek mythology. Egypt is a desert because Helio's reckless son drew the sun chariot too close to Egypt and scorched it. So I'm going to lean into that. Rain shadows from mountains and land masses has some impact but when elementals ran amok, the areas where fire elementals attacked in force because arid environments forever. Because of the ambient fire elemental energy, rain falls from the sky less often. Because crossing bodies of water is difficult and painful for fire elementals, deserts near the sea are pretty rare.
I guess since the East Colassian mountains represent the marching line of a bunch of earth elementals I should through in a couple small volcanoes where the desert and mountains meet because that is what happens when earth elementals and fire elementals mix according to my own established lore. Maybe the most active and predictable volcano can be claimed in Magicland. Volcano based forges are fantastic for crafting magic items.
This could also give nations near the mountains more access to igneous and metamorphic rock.
Real science. Weather fronts endlessly flow toward the East on Earth because of the Coriolis Effect. CE is caused by the spherical shape of Earth. On a cylinder world ...no Coriolis Effect ??
I guess no Coriolis Effect. Also, I don't think Nami the Chaotic Neutral goddess of weather would want weather to be that predictable, though she would still be limited by elemental forces because it would take more work for her to cause precipitation in areas with a lot of ambience tied to the elemental force of fire.
I do love the science lessons on the Coriolis Effect.
The Coriolis effect isn't caused by the Earth's shape, but by its rotation.
So as long as your cylinder rotates, there will be a coriolis effect.
I assume your cylinder rotates along the axis that goes through the flat surfaces?
I'm undecided to if the world spins or if the world is stationary while the sun, moon and stars rotate around the cylinder. So assuming is not a good idea.
So option one is that the cylinder of Scarterra doesn't move. Khemra and Zarthus steer the sun and moon around the world and the constelations lazily drift around the sky like detrius on the sea.
Option two is that the sky is more or less a static entity and Scarterra moves and spins, possibly fueled by the elementals in the center of the earth like hamsters on a wheel.
On the top and bottom of the cylinder there is also a Coriolis force, it bends your path in the same way it would on a flat, round, spinning plate.
There is no top or bottom to consider (happily) (?) everything beyond a barrier at the top (or bottom) of the world is: THE VOID
Any thoughts on the direction of prevailing winds?
Well said Pendrake! You remembered something from my far more than 22 word cosmic backstory!
Hmmm, I guess since the Void acts as a heat sink that would make the predominant wind cycles be north to south as the poles pull heat towards themselves. The equator would not only be the warmest, but it would be the least windy. That actually works twice because I already established that people born and raised near the poles tend to have Air infuence in their inherit traits.
Now, that's VERY basically how weather works.
I'll try and think about how that would apply to a cylinder. Most of it will probably still apply.
Since the very basic description is actually fairly complicated that explains why people think the weather is random because random often means "Affected by things beyond our understanding). I was born and raised in the American midwest where we can move from using the heater to running the air conditioner and make over and again. That's kind of why I made the weather deity Chaotic Neutral.
I will admit that me living far away from mountains and the ocean makes weather less predictable. When I spent time near mountains or the sea you could almost set your watch by when it starts raining.
Neve the less Nami is mildly interesting in providing weather that is beneficial to mortals but for the most part she alters the weather when she gets bored. That's not to say the other deities have no power over the weather. The deities can influence the weather in small ways with effort. Any cleric can learn weather magic, not just Nami though they do this seldom because Nami's priests and priestesses have a difficulty break when using the weather control power.
A lot of weather and geological forces are the results of elemental forces. Especially when elementals ran amok during the first Unmaking.
The ebb and flow from the tide marks areas where earth and water elementals fought.
Most mountain ranges are the remnants where large numbers of earth elementals marched in straight lines.
Deserts are the result where fire elementals stamped an area with their essence which makes rain fall difficult there.
I guess air elementals would inadvertantly creating prevailing wind currents but to be honest, I generally envision fewer air elementals joining the massive riots than the other three elemental types.
I guess the gist of it is Nami does what she wants but elemental forces can make certain weather easier to force. If Nami wants to make it rain in the desert or snow in the summer she has to work harder to make the weather stick.
Rivers often follow the paths of water elementals who crossed on land though rivers are less influenced by elementals. They existed before the unmaking. Mera helped direct rivers to provide water for thirsty creatures. Mera is the god of the sea but I haven't figure out how much influence she has over the sea. I do know she tries to make ocean currents easy to travel on because she is so nice and that Greymoria loves to sabotage her and make the sea and water in general more dangerous. Greymoria's followers frequently drown their victims.
Finally the Void acts likes a heat sink on the poles because the Void has Turoch's essence and it wants to consume all life. The Barrier that holds the Void at bay weakens every year on the anniversary of Turoch's death and then is strengthened as the Nine repair it. This creates Summer and Winter.
So I guess the main impacts on prevailing weather patterns are
1) The meddling of millions of elementals during the First Unmaking.
1a) Fluctuations when lesser disruptions of magic energy create small numbers of rogue elementals.
2) Proximity to the poles/Void and the fluctuations in the Barrier to the Void
3) When Nami gets bored and tries disrupting things for fun
3a) When the rest of the Nine countermand Nami's control of the weather to help their favored mortals.
4) Something with the ocean currents?
I probably will get an idea for ocean when I get around to making a parallel cosmology for merfolk and all the other sea creatures.
I don't see gravity having an effect. Scarterras kind of runs on a mythological basis. Mythology explains things that change. Lots of mythologies explain how the sun rises and sets, why the seasons change, why different areas have different climate, why the leaves fall off of trees. Gravity is constant so there are few myths about it. I'm not aware of any ancient myths about why things fall down, that's just taken for granted. Like rocks. A lot of myths involve rocks but very few myths question why rocks are there. One of my favorites is when a rock teaches a shaman the secret of building sturdy homes out of stone in exhange for the shaman teaching the rock how to fly (by making stone arrow heads).
Enough tangent on rocks. Sadly the story above relies on an animistic world and I don't see animism being a good fit for my RPG world. If I created a setting with lots of relatively weak gods instead of nine very powerful gods I probably would use animism (the idea that everyone and everything has an assocaited spirit) as a base aspect of reality. I guess it's a lot easier to make myths when the sun, mountains, and river are all sentient beings.