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    • CommentAuthorIllidan
    • CommentTimeJul 5th 2016
     
    Hey everyone. new user here.

    I have been working on a world in FT3. Really happy with it and have been tweaking. Focusing on things like axis tilt, albeido, etc to get the climate right.

    Many parts look good, but there is one thing that makes no sense to me, There isn't a single desert on my world. Maybe this is scientifically accurate given my settings, but it's settings are very close to earth-normal (but the globe in smaller and land takes up slightly more surface percentage than on earth)

    In order to get any deserts to appear I have to ratchet the rainfall so far down that the rest of the climates go into a fit and half the map seems to become tundra.

    My research indicates that about 1/3 of Earth's landmass is dessert, so I'm at a loss for how my word doesn't seem to have any. I've got a healthy mix of just about every other climate.

    I realize I can "paint" myself a desert, but that defeats the purpose here, because I'm trying to get the foundation of a world that is "scientifically accurate."

    Any thoughts/ideas?
    • CommentAuthorLoopysue
    • CommentTimeJul 5th 2016
     
    I too have noticed the lack of any really big Sahara type deserts, but I have also assumed that definition plays an important role here. For example, what some people call a desert, others might insist is savannah, or brush, or something else that similarly looses more moisture than it gains in a year through evaporation.

    This doesn't solve your problem, but is only a suggestion. How does your map look if you group the three driest climates together and call them collectively "desert"

    You might not be aware, but the estimation of 1/3 desert includes Antarctica, and only applies to the land surface, not the ocean, which covers 71% of the Earth's surface. Once you take those two factors into account the amount of yellow on your map might start to look a little more realistic.

    As for the lack of sweeping Saharas? Well, that might be down to the fact that very few of the FT3 worlds I've ever seen have continents that are as bulky as Africa, which is one huge continent. Fantasy worlds tend to have lots of coastline (or they just don't look interesting enough - lol), and anywhere near the coast is going to get at least a couple of inches more rain in a year than a place that's a couple of thousand miles inland as far as a computer program is concerned.

    If you end up having to paint on your deserts, pick areas that are shielded from oceans by mountain ranges, or which are trapped against a cold deep ocean current by mountains, like the Atacama Desert in Chile (which is one of the harshest deserts in the world despite being right next to the sea) - you having already decided for yourself how the ocean currents flow :)

    I have attached a map I sometimes stare at while I'm considering what to put where on my worlds.
      Climate regions of the Earth.jpg
    • CommentAuthorjslayton
    • CommentTimeJul 5th 2016 edited
     
    Posted By: Illidanbecause I'm trying to get the foundation of a world that is "scientifically accurate."

    FT's climate model is very limited in that it doesn't provide for heat transport via water or wind and also does not provide for moisture transport via wind. This means no rain shadow deserts behind mountains, no deserts due to distance from the ocean, and no deserts due to Hadley circulation. It's a major limitation of the software. I had always intended that the provided climate information be used just as a starting point, but lots of folks seem to have come to the conclusion that FT's climate model is somehow as accurate as climate models running on supercomputers (OK, a supercomputer at the time FT was written is a mid-level GPU today in terms of raw floating-point performance, but those parts of FT haven't been updated much since they were first written).

    I recommend reading http://www.fracterra.com/CGTutorial/index.html if you haven't already done so. It offers some suggestions for default values that should make it simpler to adjust FT's settings.

    The short technical reason for the limitations of FT's climate model is that everything in FT is point-evaluated, meaning that there isn't a truly global picture available in the computation engine.
    • CommentAuthorLoopysue
    • CommentTimeJul 6th 2016 edited
     
    Posted By: jslaytonFT's climate model is very limited in that it doesn't provide for heat transport via water or wind and also does not provide for moisture transport via wind. This means no rain shadow deserts behind mountains, no deserts due to distance from the ocean, and no deserts due to Hadley circulation.


    Hadley circulation - yes of course.

    Where the current appears to circulate (give or take a few offshoots and inflows) is called Hadley circulation. These are deep ocean currents, not surface ones, and they affect the entire global climate by heating or cooling large masses of surface water and the atmosphere directly above them. Interestingly, without the ice caps pouring heavy 'ice cold' water at just 4 degrees C into the world's deepest ocean trenches, the entire world would eventually become a baking desert, because there wouldn't be anything cooling the oceans down any more... a bit like running a car without any water in the radiator. Basically - you're in trouble if your world doesn't have at least a small ice cap at both poles.

    Posted By: jslaytonThe short technical reason for the limitations of FT's climate model is that everything in FT is point-evaluated, meaning that there isn't a truly global picture available in the computation engine.


    You really don't do yourself credit jslayton. Creating FT3 was a stroke of genius. There is simply no way people like me (who can't draw an imagined coastline for the life of them) would manage to cope all that well without it. And I really wouldn't say it was all that limited! It gives us an invaluable starting point to base our informed predictions of what might happen to those point calculated values over a 10,000 year period; taking into account the likely Hadley cells, the likely surface currents, the likely prevailing winds, and therefore the precipitation over time... it is complicated, but not impossible to 'see' a fairly realistic global climate pattern just by staring at the world on the screen for long enough. We users just have to be patient with our own thinking processes and work the magic of our imaginations.

    I'm sorry. I just had to say that. You don't seem to realise what a wonderful thing it is that you have created for us :-)
      ocean currents.jpg
    • CommentAuthorjslayton
    • CommentTimeJul 6th 2016
     
    Hadley circulation is atmospheric rather than oceanic and is more related to rainfall than temperature ( https://en.wikipedia.org/wiki/Hadley_cell ). The oceanic circulation is more important for temperature transport. FT doesn't do either, sadly.

    If you want to see how FT's engine diverges from real-world conditions, just load a height map of the earth into the beastie and marvel at wonders like the arctic Ireland (it is at the latitude of Moscow, after all, and only kept warm by close proximity to the warm remnants of the Gulf Stream) and the humid Sahara (dried out by a descending Hadley edge).

    My goal had been to provide meet ProFantasy's spec for a product while providing a rough starting point and tools to get the world to where folks wanted it to be. As a pure random generator, FT has a number of flaws (including only a single fractal function for world generation, no tectonics, no heat transport, truly hideous cratering, and so on). In its earliest incarnations, the editing tools were pretty bad. Even now, the defaults probably aren't the best. And it's a 32-bit program that tries to keep everything in memory, which limits the editing resolution. Over the last 20 years or so I have figured out solutions to most of the problems with FT, but in a lot of cases it's virtually impossible to fit those changes into the FT infrastructure without breaking existing worlds. I had a breaking change once already to fix a serious bug in the earliest FT versions and I'm not planning to do it again.

    But thank you for your kind words. I do expect that I'll be fielding the "where are the deserts" question for a while yet.
    • CommentAuthorLoopysue
    • CommentTimeJul 6th 2016
     
    Hadley cells? Yes I realised that about 6-7 hours after posting it! LOL. Never mind, its actually a similar principle - convectional currents affected by Coriolis force - but just a heck of a lot slower in water than air. I think the calculated estimate for how long a single molecule of water takes to complete the global conveyor belt of currents through the Earth's oceans is 1000 years.

    Maybe we should prepare a set answer to this question for future use?
    • CommentAuthorjslayton
    • CommentTimeJul 6th 2016
     
    Posted By: LoopysueMaybe we should prepare a set answer to this question for future use?

    That presumes that people search archives before asking questions...
    • CommentAuthorPharaohTet
    • CommentTimeSep 22nd 2018
     
    That presumes that people search archives before asking questions...


    Like I just did?
    • CommentAuthorLoopysue
    • CommentTimeSep 22nd 2018
     
    That tutorial is well worth a read ;)
  1.  
    So I see this comment come up a lot. I have done a ridiculous amount of experimentation with FT3, mostly trying to come up with different methods of getting legitimate deserts onto my world. I've learned all sorts of things about axial tilt, as well as all the stuff that affects climate.

    Before I continue on with a more general comment, I want to put up here one thing I came up with which I found intriguing. In doing the Israh tutorial, I noticed that the author often uses quite ridiculous numbers to achieve their effects, so I thought, why not try that with precipitation. Taking the earth data map provided with FT3, I focused on trying to get Africa to look like it does on the real world (because my world has a similar land mass). I settled on putting the precipitation amount at 0, and the random figure at 1000. This produced a reasonably similar Africa, but dried the Amazon rainforest out. What are you going to do?

    Anyway, the point is, using 0 precipitation and 1000 random will get you small deserts, ranging from decent deserts to mere strips of aridity. If you then play around with the setting, you'll be able to get those deserts to shrink or grow. One thing that's great about using this setting is you're also more likely to get evergreen rainforest, which is also generally lacking in the climate model. It does reduce temperate grassland quite a bit, unfortunately. One thing I did like about it is it put a desert in a place that really surprised me, actually along the equator. When I looked at it more closely, I realized that it was actually a reasonable place for a desert, since there was a lot of mountains in the region that would cast rainshadow. I liked that because the deserts weren't just in all the obvious places, just as they aren't on earth (Somalia/Ethiopia, for instance).

    The other difficulty with producing deserts is of course temperature, and I came up with an interesting idea based on axial tilt. From my research, I determined that January is 7% hotter than July, so I altered the sun setting in temperature to 1.035 and 0.965 to create a temperature map for both months. It doesn't sound like a lot, but it had a profound effect on the world's temperatures (5 C at the equator). I then varied the random category for precipitation to 750 in January and 1280 (I think) in July, reasoning that there would be more rain during the cold time of the year. It then occurred to me that for January you should really use the July map in the northern hemisphere and the January map in the southern.

    Then I had kind of a brilliant idea: why not create a dry map for the deserts of your world? You could maybe have 40 precipitation with the usual variation. Wherever this resulted in desert, you could use the values generated on the dry map and transfer them to a master map. You could do the same with the ITCZ , ocean currents, whatever.

    One final thing: maybe its just for my map, but I've actually found that the FT3 climate model is fairly accurate if you just look at which areas it predicts will be dry or wet, cold or warm. The trouble is that the range of values in both cases is too narrow. For instance, my world's temperature ranges from about -10 at the poles to around 29 on land at the equator. It should really be something more like - 58 to 34 (for regions where there is human habitation).