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Thread: How do I Climates/Rainfall/Temperature

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    Question How do I Climates/Rainfall/Temperature

    So, I just want to start out by saying that I really really admire the level of depth that the World of Gotha people go to with their mapmaking. And I'm now really wanting to be able to do this with my maps (hopefully without the use of fractal terrains cause I'm not terribly happy with any of those landshapes). What I'm wanting to do is imitate the style for the rainfall and also the level of detail with the climates on these maps in particular...

    Climate
    Rainfall
    Temperature

    I have photoshop as well, so if I could use that to do this, that would be even better. I'm just not 100% sure on how I would go about this.

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      waldronate is offline
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    If you don't like the shapes in Fractal Terrains, you can edit them ( Tutorial for Cartographer’s Guild offers some suggestions ). FT has some severe limitations in its climate model, but it's still useful for what it does.

    An important starting point to getting that level of detail for your climates is getting that level of detail in rainfall and temperature (to a first approximation, climate type is equal to a table with temperature on one axis and rainfall on another - http://www.ridgenet.net/~jslayton/climateinfo.gif has the table that FT uses). Temperature is very approximately related to axial tilt and altitude, modified by the effects of ocean and air currents (it's those last two that FT is missing). Rainfall is very approximately related to water temperature, distance from water bodies, and air currents to carry the moisture (again, FT falls flat on the air currents stuff).

    If you can get the basics of your terrain laid out, Resources for worldbuilding - geography, climate offers some suggestions for getting the rest of it.

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    Awesome. Thank you so much for the resources. I'll give FT another shot (because it is really useful when I'm not being picky). It just looks like FT just needs to have a lot of tweaking done in order to get it to look alright.

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      waldronate is offline
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    Quote Originally Posted by Paramenides View Post
    It just looks like FT just needs to have a lot of tweaking done in order to get it to look alright.
    I've learned a lot over the last 13 years since FTv1 hit the shelves.

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    I have been working on my map climate zone lately. I hope this might help you

    Biomes classification:
    most used I think: Köppen climate classification - Wikipedia, the free encyclopedia
    also useful : Holdridge life zones - Wikipedia, the free encyclopedia

    I still don't completly understand how the wind direction influence precipitation.
    For example, in summer, Chili is supposed to receive winds from the Pacific ocean. It seems to me that it is supposed to rain, but it's dry. While it north est america, where I live, the wind come from the western plains but it's humid. I don't understand this.
    I also wonder how to tell where the "strom corridor" will be in my world, mostly hurricanes but also tornadoes.

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    Quote Originally Posted by Azelor View Post
    I have been working on my map climate zone lately. I hope this might help you

    Biomes classification:
    most used I think: Köppen climate classification - Wikipedia, the free encyclopedia
    also useful : Holdridge life zones - Wikipedia, the free encyclopedia

    I still don't completly understand how the wind direction influence precipitation.
    For example, in summer, Chili is supposed to receive winds from the Pacific ocean. It seems to me that it is supposed to rain, but it's dry.
    Chile is a very long narrow country, bordered on one side by one of the highest mountain ranges in the world. This dramatically affects its climate. In the north, the prevailing winds are the SE Trade Winds, which means they come across the Atlantic, bringing rain to the Amazon Basin and northern Argentina. Here, Chile lies in the rain shadow of the Andes, and is very dry - the Atacama Desert is the driest on earth. However further south the prevailing winds switch to the westerlies, bringing rain from across the Pacific. As a result the centre and south of Chile has very high rainfall, while it's dry on the other side of the Andes in southern Argentina.


    Quote Originally Posted by Azelor View Post
    While it north est america, where I live, the wind come from the western plains but it's humid. I don't understand this.
    The prevailing winds for NE USA are the westerlies, as you say, and all else being equal, North America should be relatively dry east of the Rockies. However there's a local anomaly which dramatically changes this; the Gulf Stream. This is a water current in the Atlantic. The northern equatorial current comes across the Atlantic, where the gently curved coast of the USA acts like a big scoop, sweeping the current north up the coast. The outward flaring shape in the north then directs the current back out across the Atlantic. This has a profound effect on the climate of both North America and Europe.

    All regions experience winds that don't adhere to the prevailing wind direction. This is because air circulates around high and low pressure areas, thus the local wind direction is dependent on the position of the low or high. As the weather system moves through the area (in the direction of the prevailing winds), the local wind direction changes, in exactly the same way that wind direction reverses as a hurricane passes overhead.

    If you imagine a weather system like a giant spinning disc, it is travelling around the world based on the prevailing winds, but the disc itself is also spinning. If it's spinning clockwise, the wind direction at 12 o'clock is westerly, the wind direction at 3 o'clock is northerly, the wind direction at 6 o'clock is easterly, and the wind direction at 9 o'clock is southerly. As you can see, depending on where exactly the weather system passes through, the wind could be coming in any direction.

    As weather systems sweep west-to-east over the coast of the NE United States, the "backswing" of the system is going in the opposite direction, east-to-west, thus it creates onshore winds as it passes over. Because the Gulf Stream dramatically increases the water temperature off the eastern coast of North America, that backswing collects a huge amount of water off the ocean and drops it on the coast as it comes past.


    Quote Originally Posted by Azelor View Post
    I also wonder how to tell where the "strom corridor" will be in my world, mostly hurricanes but also tornadoes.
    Storms are driven by the same consideration. Tornadoes are a product of severe thunderstorms, and thunderstorms are created where warm and cold air mix. So-called "Tornado Alley" has such devastating tornadoes and thunderstorms because of geography. It's unusual on earth in that you have a huge relatively flat expanse of land that extends from polar latitudes in Canada right down to the tropics. Cold air sweeps off the arctic and heads south, while water-laden air off the Gulf of Mexico sweeps north.

    Unusually, there are no mountain ranges to interrupt these two air flows. As a result the water remains in the warm air as it travels hundreds of kilometers, and the cold air continues to surge south uninterrupted. When these two hugely powerful wind forces collide the result is, literally, electric.

    The only other places on earth that have such a potent mix of warm and cold air are over oceans, such as the Indian Ocean, so we don't notice the violent storms and waterspouts there as much.

    Hurricanes are different again. Hurricanes are actually the local name for a cyclonic storm, which are known by different names in different parts of the world; hurricane, tropical cyclone, and typhoon. The cause of these incredibly powerful storms isn't completely understood, but primary factors are the earth's coriolis force (which gives weather its spinning motion), atmospheric humidity, and high ocean temperature. Thus they only form in a narrow band through the tropics on either side of the equator.

    Cyclones form right through this band both in the northern hemisphere and southern hemisphere, but most of the powerful cyclones are limited to two basins; the NW Pacific and the Atlantic. A theorised reason for this is a phenomenon called the Tropical Wave. This is caused by atmospheric disturbances in Northern Africa. The prevailing winds carry the hot, extremely dry air west across the Atlantic. This region, being subtropical and tropical, is normally very humid, and as the wave passes tropic air sweeps back in. This sudden change from dry to humid air creates very unstable atmospheric conditions, spawning violent downpours, thunderstorms, and the perfect conditions for creating cyclonic storms.

    Where you find these factors on your own world, that's where you'll get this phenomena.
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    Thank you for your answer, very instructive. I did not notice the wind direction was different in southern and northern Chile or that the climate was so different. It make sense that water block most of the rain and not the wind.

    It is said that in january, high pressure zone are located in the north landmasses. While in july they become low pressure zone because high temperature usually mean more pressure. And it's the opposite in the south. I also know that having more landmass in an hemisphere make it hotter so this will impact wind direction. Like Asia dragging the tropical weather and heavy rain toward India... I suppose water flow with the same rule than air exept that it can't cross over land.

    I heard that having an open ocean in the south without obstacles made the earth climate more unstable, why is that so ? The way I see it, it's more unstable that way but it probably mean that colder and hotter water get mixed together wich in turn create rainfall wich is good for life. What impact would it have to have no countinuous belt in the south? Or elsewhere in a fantasy world.

    May I have your opinion concernig the main wind direction of my world map ? I would really apreciate it. The world of Ilvakor
    It's pretty rough but I might do a better version when the climates are settled. And of course, the world is not complete since I still don't know what lies on the est. There will probably be a continent in a northern latitude smaller than the one in the west and possibly others but even smaller. The most important being in the extreme south maybe in the middle of the map.

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    Quote Originally Posted by Azelor View Post
    It is said that in january, high pressure zone are located in the north landmasses. While in july they become low pressure zone because high temperature usually mean more pressure. And it's the opposite in the south.
    Kind of, high pressure systems, or anti-cyclones, are warm, while low pressure systems or depressions are cold. Obviously with the shift of seasons each hemisphere is warmer or colder, and therefore is dominated by high or low pressure systems, but you still get both at all times of the year.


    Quote Originally Posted by Azelor View Post
    I heard that having an open ocean in the south without obstacles made the earth climate more unstable, why is that so ? The way I see it, it's more unstable that way but it probably mean that colder and hotter water get mixed together wich in turn create rainfall wich is good for life. What impact would it have to have no countinuous belt in the south? Or elsewhere in a fantasy world.
    Well, the Antarctic Circumpolar Current (ACC) is pretty important, although it's not fully understood what its impact is on the earth. It certainly makes the southern hemisphere a lot colder than it would otherwise be, which is white Antarctica is so much colder than the Arctic. The ACC is also thought to be a major driver of Thermohaline circulation, which is responsible for the ocean's currents, and the convergence zone between the ACC and sub-polar waters causes an upwelling of nutrients leading to a huge surge in the phytoplankton population which acts as a giant carbon sink, absorbing the equivalent of about 12.8 million tonnes of CO2 a year.


    Quote Originally Posted by Azelor View Post
    May I have your opinion concernig the main wind direction of my world map ? I would really apreciate it. The world of Ilvakor
    It's pretty rough but I might do a better version when the climates are settled. And of course, the world is not complete since I still don't know what lies on the est. There will probably be a continent in a northern latitude smaller than the one in the west and possibly others but even smaller. The most important being in the extreme south maybe in the middle of the map.
    It's a bit hard to really make any judgement about prevailing winds without knowing where your map fits into your globe. If you could mark some lines of latitude (like the polar circles, tropics, and equator) it would be possible to offer some feedback.

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      Azelor is offline
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    I admit it might not be claer because I did not follow any sort of convention to do it. The green line in the middle is the equator while the red lines are the tropics. Each black line is represent 15 degree of latitude.

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    Quote Originally Posted by Azelor View Post
    I admit it might not be claer because I did not follow any sort of convention to do it. The green line in the middle is the equator while the red lines are the tropics. Each black line is represent 15 degree of latitude.
    Ah, I must be stupid, I only actually looked at the first picture and didn't see the others!

    Your wind patterns more or less match, except for a single error (assuming an earth-like planet) which is that your ridges are in the wrong place. The subtropical ridges are on the tropics, but they're actually at 30 degrees. You should also move your second ridge (which is between 75 and 90 degrees) to directly over the pole.

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