What are good resources for figuring out climates?

[Sayetsu]

I have Fractal Terrains 3, but I don't imagine the climate is "temperate forest" seemingly everywhere that's not mountainous...so how could I figure out climates for my world knowing, say, their geographical area/features and average rainfall and temperature? Thanks!

[jqavins]

I have Fractal Terrains 3, but I don't imagine the climate is "temperate forest" seemingly everywhere that's not mountainous...so how could I figure out climates for my world knowing, say, their geographical area/features and average rainfall and temperature? Thanks!

Search in the World Building subforum, and you'll find several old threads on the subject, with some good information from people who know lots more than I do. Temperature changes with latitude, obviously. Prevailing winds switch directions in latitude bands. Proximity to oceans and inland seas makes a big difference, being downwind of a mountain range tends to make deserts (but not always) and stuff like that.

I don't recall, in any of those threads or elsewhere, reading of software that would automate this, which is something I would love to have.

What if a long, tall, north-south mountain range, like the Rockies, were to cross from one prevailing wind band to another. Then the east side (or west) would be upwind in one region and downwind in the other. That could lead to potentially really interesting climate border regions. Or maybe not so interesting in the end. Hmm...

Anyway, if you'd like more responses to this, you should message an admin and ask to have the thread moved to World Building.

[Sayetsu]

I was rushing and didn't see that forum, heh. I'll try to figure out how to do that. Thanks!

[arkham618]

I have Fractal Terrains 3, but I don't imagine the climate is "temperate forest" seemingly everywhere that's not mountainous...so how could I figure out climates for my world knowing, say, their geographical area/features and average rainfall and temperature? Thanks!

http://web.archive.org/web/201306191..._cookbook.html

[Lvl 2 Expert]

Mountain ranges, as jqavins said, work wonders on your rain distribution. In front of them, seen from the prevailing wind direction, the climate is wet, behind them it's dry. Prevailing wind direction does not have to be the same for the entire map. For instance: in real world Europe much of the time there is a low pressure area hanging somewhere above Britain or the northern Atlantic ocean. A low pressure area on the northern hemisphere swirls wind around counterclockwise (this does not work with a bathtub, but it does with a low pressure area) while also swirling out lot of rainclouds, especially if the area is over water. This means that area's closest to the general location op the low pressure area, like Scotland, are wet with high winds varying in direction. Area's a bit further away, like the Netherlands, have a dominant wind direction and plenty of cloudy and sort of rainy weather, while a place further off or sitting behind mountains, like Spain, will possibly be drier. The result might look a bit like this. So, try to think up what the dominant weather systems could be. The hurricane breeding field southeast of the US are also a good example of a weather system that has a big impact on the larger region.

Also noticeable on that map linked under the word this is the rainy spot over southeast Belgium. Those are the Ardennes ("the Bulge"). Clouds typically hang at an altitude between 1 and 10 kilometers, these mountains are at their highest peaks under 700 meters tall, and still they have typical mountain weather. There can be rain for the entire day in one valley while it's dry in the next one and everything. What happens to the air at lower altitudes matter at higher altitudes.

Another factor can be sea currents, warm ones coming from the tropics or cold ones coming in from the Poles. These are typically pretty constant over large pieces of coast line (although things like el nino can thoroughly screw with them between years, so if that sounds cool maybe look into that kind of stuff). Sea currents mostly influence temperature, they don't have a big effect on humidity. So combined with the wind direction you can have an island with a single mountain and around it four climate zones: desert (downwind, on the side with the warm current), a more rainforest like region (upwind, upcurrent), a wet temperate zone (upwind, downcurrent) and a cool and dry place with plains (downwind, downcurrent).

Elevation of course plays a big part as well. Low lying areas downhill from large basins are where the rivers go and form delta's and swamps.

And then of course there is how close places are to the equator, assuming an earth-like spherical planet revolving around a sun. In fact, I'm going to assume a planet with seasons. That's because as you may know the imaginary line around the globe where the sun is directly overhead changes with the seasons, going up and down between the tropics of Cancer and Capricorn. This imaginary line gets a lot of rain, while places further away are more arid, as you can see looking at the places between Congo and the Sahara desert. Places close to those two tropics lines have a single rain season and a long dry season. Places in between them have two wet seasons. If they're not nearly on the equator, one of those dry seasons will be longer than the others. Places well outside of the tropics have summer and winter as many of us know them. In places close to the shore of with a dominant wind coming from the sea the seasonal changes are less drastic than in landlocked places.

All in all a lot of your map is still going to be temperate forest, but you might be able to distinguish between different types (a little bit similar to this maybe?) based on how wet and how warm you expect them to be.

[Yora]

I think there's really only two principles that need to be understood to make the climate reasonably believable: Maritime and continental climate, and rain shadows.

Well, maybe also that there tends to be a desert band that separates tropical forests from temperate forests, but that's not such a hard rule as there are also many other factors playing into it.

[Sayetsu]

@_@ So complicated...but probably worth it. Thanks.

[brian 333]

Earth's climate is unique to the Earth of today because of the distribution of land masses and oceanic currents. Our climate today is not the same as it was before the Panama Straits closed or when Mount Everest was Everest Knoll.

England is not currently under a massive glacier like Greenland's because the Gulf Of Mexico is (relatively) shallow, allowing it to heat up under the sun. When the Florida Straits eventually close and choke off the Gulf Stream in a few million years, Northern Europe will have a climate similar to Alaska's.

Smaller oceans and seas will make weather much more volatile, while larger oceans make for calmer weather. Why? Thermal conductivity. Water disperses heat much more efficiently and evenly while stone does not, creating hot spots and cold spots, which creates atmospheric turbulence. The rapid heating and cooling expierenced on land as the sun rises and sets does not happen on the ocean because stone only warms a few centimeters deep and cools rapidly when the sun sets, but water heats many meters deep and thus never gets as hot or cold as stone. Sit on a stony beach with your feet in a tide pool at noon and midnight to experience this effect.

It isn't necessarily true that mountains cause rainshadow deserts. Look what's downwind of the Andes mountains, for example. Of course, the Andes cross several climate bands and prevailing winds change as you travel their length, but all of South America's true deserts are on the ocean side of the mountains.

So, water depth, water volume, and oceanic currents play a massively huge role in any planet's climate. Even on Venus and Mars. Water can bring warmth to polar regions and cold to tropical zones. (Iceland and the Galapogos, for examples.) Air currents are secondary heat distributors at best.

[Sayetsu]

STOP IT. Kidding...but yeah, geez, I don't know how deep to go here. ._. Thanks, though.

[brian 333]

My advice to all world builders is to only sketch outlines. If you get too detailed you'll have generated information your players will never use and robbed your game of time devoted to fleshing out the immediate environment in which they travel.

So, don't worry too much about why your city is subjected to periodic intense fogs until players start to ask. Sketch out your world and put deserts, forests, glaciers, and volcanoes where you want them. You can always go back and retcon.


One example: I had a desert bumping into a forest in an early campaign map. It can happen...

My players returned to the area and protested when I started describing a vast grassland.

"Oh, that was because you guys were unaware that the region had a huge wildfire just before you got there. Now the grass has grown back."

[Lvl 2 Expert]

"Oh, that was because you guys were unaware that the region had a huge wildfire just before you got there. Now the grass has grown back."

That attitude is probably the best advice in this thread.

If you don't know how deep to go, start spending your time and energy on other stuff. If later on you wish you did it differently, no problem. (For a campaign, is a little different when you're writing a tv series or something.)

If you want to cheat, have a region that at least to you is kind of similar to a real area. Like say North America. Big slap of land, two coastlines, mountains down the middle, hot in the south, cold in the north. Need to know the climate in a northern place east of the mountains? Find a corresponding real city, look it up on Wikipedia and look at the climate section. Google a nearby nature reserve to get an idea of the environment. Bam, instant real feeling continent.

(And then add creepy ever-foggy forests, huge sand dune deserts and large inland swamps just because you feel like it.)

[Lleban]

STOP IT. Kidding...but yeah, geez, I don't know how deep to go here. ._. Thanks, though.

It can feel very overwhelming and there can be a lot of judgment calls. I think i might be a good idea to approach the issue in broad strokes so looking at the chart at the bottom of the climate cookbook that arranges zones relative to latitude is a good place to start.

Remember though you have the ultimate agency over what the climate of a particular area is and good luck XD.

[Sayetsu]

Along those lines, I just read there would be no Coriolis effect on my world: it's on the inside of a sphere and it's the "sun" - which is a two-dimensional disc bright on one side - that spins. How could I create different climates? <_> I thought about maybe making one pole generate heat and the other absorb it, but that could have weird effects....

[Knaight]

Along those lines, I just read there would be no Coriolis effect on my world: it's on the inside of a sphere and it's the "sun" - which is a two-dimensional disc bright on one side - that spins. How could I create different climates? <_> I thought about maybe making one pole generate heat and the other absorb it, but that could have weird effects....

That should create different climates all on its own. Consider a simplified model, with only three areas. There's the sun disk itself, there's a band around the sun disk that faces the flat surface dead on, and there's the area on axis that only faces the edge. The band around the sun disk is effectively equatorial, getting the most sun, with noon being a full blast of it. The on axis area gets extremely little sun, and is effectively a polar region.

This isn't spinning, so you can then figure out approximate wind conditions pretty easily. Effectively there are two major circulation cells, one to the top pole and one to the bottom from the equator as hot air, then back as cold air. Geography then affects much of the rest, and it's all pretty straightforward to roughly approximate.

[brian 333]

Fluids and gasses inside a container don't behave very differently inside a container than outside, except that the container bounces escaping molecules back in. If your sphere is spinning it will indeed produce coriolis winds. Perhaps they will be on their sides instead of vertical, (Terrestrial tornados start out that way and gravity stands them up,) but the storms occur because one air mass tries to go over or under another, causing the air to 'roll' in between the two layers very much like when your bedsheet rumples beneath a blanket when you slide it off the bed.

As long as your heat distribution is uneven air will heat unevenly and do its best to balance out, which creates winds. These winds, moving over a rotating spherical surface, will tend to wrap around when one end of the wind system is in a faster moving zone than the other. On Earth this differential is about 1000 miles per hour over the 6000 mile arc from the equator to the pole. But even if your sphere does not rotate in order to create stable wind patterns, you have described cold aress and warm, which by itself will drive winds. Depending on the intensity of the heat difference, you could have rare storms of mild nature to endless lashing storms between the fire and frost zones.

As you have stated it, I'm not certain how your sun works. It seems you imply it does not rotate relative to the sphere, creating two daylight zones divided by a twilight ring on the surfaces of the sphere facing the edge of the sun disc. The broad outline of such a system would be two permanent hot zones where the disc focuses its radiation and a permanent cold zone facing the disc's edge. This would force warm air to rise and try to spread out, drawing air in from all directions beneath this rising mass, creating lower air pressure in the circle around the massive heat plume which draws down air from higher up which draws air from the warm plume which rapidly compresses releasing moisture as it falls in the cold twilight zone from whence it is drawn in toward the plume. The two hemispheres would mirror one another, but the result even without rotation of the outer shell would be a warm air mass climbing over a cold one, (which is how tornadoes form,) and as the winds move inward along a curved surface, they will be forced into an ever-smaller front creating turbulence as air masses jostle and heat up. This might well organize into a giant circular wind pattern if mountains and seas don't break up the lower atmosphere into several sub-cells which could produce counter-rotating cells which, while not true coriolis storms, would look like them and act like them. Intensity depends on heat differential and water content.

Your stationary disc might illuminate on one face while the other goes dark, then the dark face could illuminate while the light side goes dark, creating days and nights with little change to the system described above except for a bit more atmospheric volatility.

However, you might consider a spinning solar disc with one face permanently lit and the other permanently dark. This would screw up the heat plume thing totally. You would have arctic zones which never thaw, but otherwise this might more closely mimic Earth's climate banding by more evenly distributing heat through a tropical zone.

A final note: gravity. The above was written assuming Earth-like gravity at all points on the inner surface of the outer shell.Diffferent gravity will create all kinds of different results.

[Sayetsu]

Brian 333: Yes, only the disc is spinning, but I assume it is like a spotlight in that the intensity gets stronger toward the center of the illumination. (That's how it works, right?) Would this create more varied climes? And no, the sphere isn't spinning, so I need to figure out another way to make wind. (Excuse me!)

Knaight: Would you please explain that model differently? I'm confused. Are you talking about the land or the disc (which is two-dimensional)?

[jqavins]

A stage spot light is designd to make a disk (or other shape) that's nearly uniform. A uniformly luminous disk would throw a pretty much uniform pattern within a beam perpendicular to it, and fade outside that spot much like a point source. A point source at the center of a sphere gives uniform illumination to the sphere's inside surface, rather than fading as it would when shining on a plane.

On the other hand, if you want a source that shines a diminishing amount of light at increasing positive and negative latitudes, well, you're the world creator and you can have what you like. We could even work out the beam geometry for you if you really care, but you can just say "This is what happens on the surface" and be done with it. Then take the weather from there, since this is a discussion about weather, not optics.

[VoxRationis]

(And then add creepy ever-foggy forests, huge sand dune deserts and large inland swamps just because you feel like it.)

As a native, I must speak up and say that the foggy forests are not "creepy." They're cool and pleasant and charming.

[Lvl 2 Expert]

As a native, I must speak up and say that the foggy forests are not "creepy." They're cool and pleasant and charming.

When nobody's hunting you, when the mist isn't an unnatural color of grey and doesn't seem to be alive and without the DM playing a loop of horror movie "there's something wrong with these children but you don't know what" music, sure. Then they are super pleasant and the way the light plays with the trees and the banks of mist is brilliant. But these are specifically creepy ever-foggy forests. Just like there's deserts and then there's specifically harsh deserts, where hallucinations born from dehydration become an issue roughly as soon as you step out of the shadows.

[Sayetsu]

Thread just derailed. xD Anyway, thanks, all.

[Knaight]

Knaight: Would you please explain that model differently? I'm confused. Are you talking about the land or the disc (which is two-dimensional)?

Sure. Lets talk about the two dimensional simplified case. You've got a short line in the middle of a circle the sides of which constantly emit light towards the circle (essentially this is a time average of the disk for any cross section containing the axis of the disk).

Now consider any point on the circle. Calling the short line AB and that point C, you can make a triangle ACB. The angle ACB to the disk changes depending on where on the circle you put it. The higher that angle, the more light (and thus heat) you get. The lower that angle, the less light (and thus heat) you get.

Getting into the exacting parts of the math gets into some ugly trig pretty quickly*. Instead, you can actually draw it out or just look at extreme cases. If you've got a point in line with the disk, the angle is 0. It's a cold spot, and it exists at both poles. If you've got a point in the middle, you get a higher angle. This is a hot spot, and it nicely corresponds with the equator.

You get a pretty familiar pattern, really. You just lose some of the complications to air cells caused by the Coriolis effect.

*It's not that bad really, but if math isn't your thing it's not likely that helpful, and that's the sense I'm getting.

[Sayetsu]

Yes, I've only had Calc I. I like the aforementioned "because this world" explanation. Thanks, though!

[Knaight]

Yes, I've only had Calc I. I like the aforementioned "because this world" explanation. Thanks, though!

It doesn't actually need any calc. If you define the line such that at x*=0 around the circle you're facing it perpendicularly, and thus at maximum sunlight S, you get a sunlight at any given point of S(abs(cos(x))). For the 3D case this extends to S(abs(cos(x)cos(y**))), but you lose the y term because of rotation. The easiest way to demonstrate this to yourself is to think of the point on the circle as static, replace the circle with a line to the center line's middle, then just rotate that.

So you don't get seasons (with a bit of axial tilt you totally can), but otherwise that looks pretty much exactly like what we see on Earth.

*Theta, but this isn't a piece of paper I'm writing on or the MS Word equation editor.
**Phi.

[brian 333]

Except that Trade Winds blow from the poles to the equator rather than from West to East.

One might presume this would lead to a colder climate, (cold air flows under warm,) but heat extraction will be the real problem. On Earth we lose the majority of our heat into space, (even with global warming.) On Hollow Sphereworld there must be a mechanism to prevent heat loss through the floor so the ground doesn't freeze, (insulation would also prevent any stars from cooking the world for a while,) but which enables heat loss from the atmosphere. Without such a scheme, the central sun-disc would just keep dumping heat into the atmosphere and the ground would suck it away, and at that point it's a matter of heat input minus heat output that determines if your world becomes a freezer or an oven.

My headcanonon for this is an underwater radiator system which pumps (relatively) warm water from the depths of the ocean to radiators on the outside via superconductors. Not only would strategically located radiators prevent oceans from overheating, they would also create cold spots which force water currents to flow. Theoretically such a system could direct currents, drawing warm surface water to polar zones, thus creating a warmer polar region and more volatile weather there.

Now we might consider what is in the neighborhood of our world. I have approached this as if the sphere was in interstellar space. It could as easily have a second atmosphere and orbit a sun, which opens another can of beans which I won't try to serve to you guys.

*edit*

My head just exploded with the possibilities:

This is a very low thrust spaceship on a thousand year journey, and the oceans and atmosphere on the outer surface are frozen, waiting for their arrival at a target star to warm them up. They will be sterile but filled with organic matter, having beome fertilizer for future colonization efforts. In this case, those who terraform and colonize the sterile outer surface will be practicing for their eventual colonization effort on worlds orbiting their target star. After that colony is established, Hollow Sphereworld refuels, repairs, and preps the outer surface for deep freeze, (instant insulation!) and then takes off for the next target star.

Or, the world is a zoo, containing the remnants of an endangered species called humanity.

Or it is a refuge or jail for political dissidents with guards to prevent their getting out or disseminating propaganda. Perhaps the jailors died off or abandoned their duty, or perhaps they are still there waiting...