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Thread: The Köppen–Geiger climate classification made simpler (I hope so)

  1. #1
    Guild Expert Azelor's Avatar
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    Default The Köppen–Geiger climate classification made simpler (I hope so)

    I see that lot of people have a hard time with their climates when they are creating their world. I'm not an expert, but I'm trying to make it simpler when it come to the climatic zones.

    I used this as the main source of information : Köppen climate classification - Wikipedia, the free encyclopedia
    But also other pages and some scientific articles. The information is there (most of it) but it's not very easy to understand. The first part I did was to collect the info on the wiki and also elsewhere to get a clear definition for each climatic zone: what it is but also where to place them: where they are the most likely to appear. It ended in something relatively complex and a long document.



    note : My main goal was to find if there was a link between the climate and population density. And if so, to find what density would be for one specific climate.
    I realized I had a serious issue with a state with similar climate to India and somewhat similar size but the population was about only 9 millions people. I did not make sense and I had no answers how to get population density numbers right.
    I also happened to have no clear idea on where to place the climates. That's why I'm doing this, and hopefully I can work on the second part after this one is finished.

    Click image for larger version. 

Name:	koppen classification graph.pdf 
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    Last edited by Azelor; 08-24-2015 at 05:13 PM. Reason: File contain too many mistakes, will be back

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    Guild Member Gracious Donor Iggy's Avatar
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    I tried to open the file but OpenOffice tells me it's damaged. Does that document come in any other format?

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    Guild Member Gracious Donor Iggy's Avatar
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    OpenOffice Writer can read and write .doc files just fine. Except for this one.

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    Guild Adept Pixie's Avatar
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    I've read the whole thing, it is helpful indeed Azelor.

    Being a science teacher and an amateur climatologist/geologist (in fact, an amateur world-builder), I can follow all of it pretty easily. Dunno how less science savvy folks will manage it, but it doesn't seem complicated.
    I think it is a very valuable add-on to the tutorial I (we) are currently building.

    It made me think of one more climate map that would be very useful: a cross-reference between rain pattern and temperature, to make a two-colored map separating areas where evapotranspiration is greater / lower than precipitation. This could perhaps be helpful (do you think it would be helpful?)

    Picking up the word usage in my tutorial, what do you think of this?
    Lower precipitation than evaporation (DRY seasons)
    Very Hot + Moderate/Low/Dry
    Hot + Low/Dry
    Warm + Dry
    Roughly equal precipitation to evaporation (MODERATE seasons)
    Very Hot + Wet
    Hot + Moderate
    Warm + Low
    Mild + Low
    Cold + Dry
    Very Cold + Dry
    Higher precipitation than evaporation (WET seasons)
    All remaining combos

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    Guild Apprentice Corvus Marinus's Avatar
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    Breaking down the meaning of each of the letters is really helpful in understanding the details of the system. And I think Part II: Climate Zones will be very useful; it's a lot clearer than Wikipedia. The formulas in Part I, for me (not very science-literate), do not translate into immediate usefulness in worldbuilding; but I can easily take Part II and use it to "proof" my map after it has gone through Pixie's system.

    If I am still around when you have a final draft, I will happily check it for spelling/grammar/formatting, if that is something you'd appreciate.

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    Guild Expert Azelor's Avatar
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    Quote Originally Posted by Pixie View Post
    I've read the whole thing, it is helpful indeed Azelor.
    Good to know.

    Were you considering a map or some info graphic like this one : http://powerfulinfographic.com/wp-co...parency-11.jpg
    I don't know about the idea. There is a relation between temperature and minimum precipitations to avoid desertification. Did you know that the Sahara would need between 3000mm and 6000mm of rain per year to become a moderate climate similar to Spain? That's a lot of water and it's just the minimum.

    There is a part in the guide where I talk about yearly precipitation not seasonal. The problem with the classification is that it compares the driest month with the wettest without taking in consideration if the driest month is really dry. Sometimes, it's not the case. It's considered dry only because the wet month receive a lot more rain. So the letters s and w are more or less valuable here. At the equator, at least we know that under 60mm it's considered dry.



    edit : this ! http://en.wikipedia.org/wiki/Aridity_index

    and this : http://upload.wikimedia.org/wikipedi...dity-index.png

    I'm now using this from the Trewartha wikipedia page: BW and BS mean the same as in the Köppen scheme, with the Köppen BWn climate sometimes being designated BM (the M standing for "marine"). However, a different formula is used to quantify the aridity threshold: 10(T − 10) + 3P, with T equaling the mean annual temperature in degrees Celsius and P denoting the percentage of total precipitation received in the six high-sun months (April through September in the Northern Hemisphere and October through March in the Southern).
    If the precipitation for a given location is less than the above formula, its climate is said to be that of a desert (BW); if it is equal to or greater than the above formula but less than twice that amount, the climate is classified as steppe (BS); and if the precipitation is more than double the value of the formula the climate is not in Group B. Unlike in Köppen's scheme, no thermal subsets exist within this group in Trewartha's, unless the Universal Thermal Scale (see below) is used.
    Last edited by Azelor; 08-24-2015 at 01:26 PM.

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    Guild Expert Azelor's Avatar
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    Hey, I got some numbers!

    Replacing this :

    • If less than 30% of annual precipitation occurs in the summer : Annual precipitation (mm) < 20 × average annual temperature (°C)
    • If more than 70 % of annual precipitation occurs in the summer: Annual precipitation (mm) < 20 × average annual temperature + 280
    • Else : Annual precipitation (mm) < 20 × average annual temperature + 140
    o If annual precipitation is < 50 % of the threshold = BW: desert climate
    o If annual precipitation is between 50 and 100 % = BS: steppe climate

    by this:

    if the annual precipitation (in centimetres)

    are Greater than R= humid
    are Smaller than R but greater than R/2= semi-arid
    are Smaller than R/2= arid

    R=2 x T if rainfall occurs mainly in the cold season (s=summer dry)
    R=2 x T + 14 if rainfall is evenly distributed throughout the year (f)
    R=2 x T + 28 if rainfall occurs mainly in the hot season. (w= winter dry)
    (T= mean annual temperature)
    Last edited by Azelor; 08-24-2015 at 01:21 PM.

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    Guild Adept Pixie's Avatar
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    Hmm, this complicates things a little bit. But at the same time, it helps. It helps because now we can get a workflow that will yield more accurate climate maps and it complicates because that workflow will be a little more messy now.

    I tried to build a humidity map based on this info and on the scheme I mentioned earlier. It doesn't fit with climate predictions made like I suggested in the other thread in some places - namely, areas classified as savanna/monsoonal close to the tropics now seem Arid (desert?) all throughout the year and steppes at higher latitudes now have a properly Humid season, making them maritime/mediterranean.

    Azelor, you have definitely raised a point that can't be overlooked. I will need to review my stuff Thanks for that (or not! no, seriously, thanks for that)

  9. #9
    Guild Expert Azelor's Avatar
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    You also need to be cautious with the numbers. For example, Jaipur is classified a steppe but receive a little more than R. Inside one climate one can see huge differences. Lisbon (Csb) is a Mediterranean climate but R=4 it's pretty wet. While Los Angeles (Csa) is barely above 1. It's not always clear because categories includes a broad range of possibilities.

    I like these formulas because they take into account that precipitation have a different impact depending when it fall.
    Logically, if precipitation evaporate at a slower rate in winter, the water (or snow) will stay longer in the environment and thus will have a bigger impact on nature. In theory.

    Two cities receive the same amount of precipitation for the year. City A is summer dry and City B is winter dry. Over the course of the year, which of the two cities will be the driest?




    areas classified as savanna/monsoonal close to the tropics now seem Arid (desert?) all throughout the year and steppes at higher latitudes now have a properly Humid season, making them maritime/mediterranean.
    plausible, but having a wet season does not always make the steppes a maritime/mediterranean climate. Only if they are not too far from the water.

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    Guild Adept Pixie's Avatar
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    Quote Originally Posted by Azelor View Post
    I like these formulas because they take into account that precipitation have a different impact depending when it fall.
    Logically, if precipitation evaporate at a slower rate in winter, the water (or snow) will stay longer in the environment and thus will have a bigger impact on nature. In theory.
    Yeah, that's the basic reasoning I think. That's what made me review the whole process - I am now going combo by combo, it becomes a huge table.
    5 january temperature levels x 6 january rain levels x 5 july temperatures x 6 july rain levels.... 900 entries.
    The original idea is to simplify climate prediction, 900 entries isn't simplifying. Still a work in progress...

    Quote Originally Posted by Azelor View Post
    Two cities receive the same amount of precipitation for the year. City A is summer dry and City B is winter dry. Over the course of the year, which of the two cities will be the driest?
    Did I say I am a science teacher? This is easy, when most of the rain falls in winter, moisture is available for longer. Thus, the location with rain in the summer is the driest.
    However... plants metabolism is very dependent on sunlight, so the location with rain in summer may have more vegetation cover as both factors for plant growth coincide, and a dry hot summer requires plants adapted to drought, which normally means smaller leaves and slower growth rate.

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