Aristotle said:
I was working on a planet with no true oceans. A planet that was mostly land. I was thinking of making it small, say about the size of mars, so it would have roughly the same land surface area as the Earth. My concern was that I didn't want it to be a desert world or an ice ball, and those seem to be the most likely choices for the planet I am describing. I was hoping to find some science to explain why my world is the way it is. Of course the science doesn't need to be overly deep. It's a fantasy world and I'm fine with "it's magic" being the final verdict.
on first look my thought was that a high ammount of volcanism would be needed to maintain the planet at a temperate level. there are some problems with high volcansim to low/ocean area though - the biggest one is of oxygen generation, the second largest being of co2 removal.... but we'll skip that for now, this is a kind of nitpicky detail that would get really annoying to try and figure out for a game.
Aristotle said:
I was looking at including 4 primary biomes (there would be rivers, forests, and such in each as appropriate). There would be a large desert area with no seasonal change other than hot days and cold nights. I was guessing the best place for this was a pole (likely leaning towards the sun). There would be a vast grassland/savannah dominating a large portion of the world. It would be covered in seas of grass from two to six feet tall. It would be warm year round, with an annual wet season (possibly a cascading wet season since the area is so big?) that floods the lower plains. Then there would be a swamp area (swamps, bogs, everglades, or whatever) with a great deal of shallow standing water. And lastly there would be a large forbidding rainforest region. It would be warm year round with a short season of high heat. It would be littered with lakes and streams fed by near continuous rainfall.
the problem with the ammount of rainfall you are describing is the lack of oceans to generate all the arial moisture - for a good solid raincloud, you need heat and standing water in the same place.
my suggestion here is to look at a map from the book Blue Mars, by Kim Stanley Robinson - it showss a possible result of a martian terraforming effort, where the surface is approximatly 70% land area, and 30% ocean. mars, in this case, is neither warm nor wet, but it is viable for life.
how to change this up? there's a couple of different (though, honestly, not-really game affecting ways) things you could do:
1) put your planet closer to the sun than mars is - earth-like distance is perfect for an active hydrosphere
2) go back in time - the planet should be younger!
3) give mars a more iron-rich and dense core, and make that core still spin (as earth's) to generate a magnetic feild - this will decrease ambient radiation (not by too much), and stimulate plate tectonics (so that you get high volcanism).
Aristotle said:
Mountains and canyons are common throughout all 4 areas. Earthquakes are frequent and volcanic activity is fairly regular in remote locations. Rivers, some much larger than anything we have on Earth, can be found in all areas. There are many small and large rivers in and near the jungle and swamp areas. Fewer in the grasslands (except during the wet season), and only a couple in the desert. I figure many of them start in the mountains and the rainforest, and most of that water makes it's way to the swamp region, collecting minerals and becoming more and more brackish as it goes until it finally becomes unusable near the swamp area.
at this point i'd really tell you to go read the mars trilogy by kim stanley robinson, if you have time.
honestly, rather than trying to scientificaly explain it, i'd go with an "it's magic" and remember the important differences between a mars-type world and an earth-type:
the horizons will be signifigantly closer.
gravity will be less - jumps will be easier, falling damage less
the atmosphere will be thicker at higher altitudes - gravity doesn't hold the air down so much
