In my attempt to work on a method based on Pixie's tutorial I came up with the idea of recreating the climates of Earth using the tutorial to see what needed improvement.
What model could be better than Earth?
The source of the data is include in these pictures.
Real world data:
The elevation map.
Temperatures for January and July. No data for Antarctica.
Precipitation for January and July.
The rest of this post is not mandatory for the tutorial.
How to determine if one area is dry ? Using Excel
I changed the precedent formula to this from the Trewartha Wikipedia page:
2(10(T − 10) + 3P)
with T equalling 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 evaporation is smaller than the average precipitation = humid
if evaporation is bigger than the average precipitation but smaller than the max = steppe
if evaporation is bigger than max = desertThus if one area has an average temperature of 35°C : severely hot + severely hot (probably impossible on Earth) the default minimum precipitation required to assure it's humid is 10(35 − 10) + 0 = 250
Then, we add the % of yearly precipitation falling in the 6 hottest months and multiply by 3. If it fall evenly during the year, the % is 50. So ... 250 + 3(50) = 400
But we still need to multiply by 2, to get 800.
So if precipitation are under 800, it's not humid.
Details:
The average yearly temperature is based on the fact that January and July are always the coldest/hottest months and that the temperature change at a constant rate at each month (of course, it's not like that in real life). Thus, in order to get the yearly average temperature I make the average of the lowest and the highest. As simple as that.
For the precipitation, in order to have the yearly precipitations, I make the summation of the precipitations for summer and winter (by previously multiplying the precipitation of January and July by 6).
Each temperature combo has a different aridity threshold but many do share the same numbers because it's based on the average temperature. Once we have the individual threshold for each (250 for severely hot + severely hot),
we need to figure how much rain each precipitation combination will give and how they are sprayed during the year.For example, a very wet area receive between 100 and 200 mm of rain in summer but less than 10mm in winter. I need to find the average precipitation here. To do that : min + max/2
min = (6*100mm) + (6*0mm)
min = 600mm
Max=1260mm
600+1260/2 = 930mm that's the average yearly precipitation for one of the 36 rain combinations.
When we have all the 36 averages, we need to find out the T from the formula. Average summer precipitation/ total precipitation.
Total= avg summer + avg winter
avg for a particular season = min+max/2
The example above would give : (100+200)/2 + (0+10)/2
or just divide 930 by 6 = 155
Now (100+200)/2= 150mm falling in summer (July)
so 155/150 = 97% of the precipitations fall in the summer
Thus the total of the Threwartha formula is 2(10(T − 10) = 800
and we add 800+3P = 800 + 3(97)
= 1091mm , that is the precipitations required to keep the place humid.
All that give us the requirements for severely hot + severely hot but just for 1 or the 36 rain combo...
When all the combos are done, we need to do it for the other temperature combinations ( some will share the same numbers)
IF THIS IS NOT CLEAR, I WILL POST THE TABLE MADE WITH EXCEL. It's not quite huge as it look.
With that table, we compare the numbers with the previous table (the one indicating the total yearly precipitation, to find when a temperature combination is humid, steppe, or desert.
When that is done, it gives me a nice huge table with 3600 little square full of colors!
Next, it's with Photoshop. Ideally this process from here can be automated with actions/scripts. That's the step 7 of Pixie's tutorial. A brief description:
What the script does:
-It start by making some dummy layers and adjustments to the different maps for technical reasons in order to be able to select all possible combinations.
-Select the different temperature combination and create a new layer for each.
-Using the temperature layer, he regroup them to create the major temperature zones from Koppen: A,Ca,Cb,Cc,Da,Db,Dc,Dd, tundra and ice caps. The last two don't need to take in consideration the precipitation, so they are done at this stage.
-Select the different rain combination and paint them in black on one layer each.
-Regroup the rain combo with all that share the same characteristic for when a specific temp combo is arid/or not.
Most of the rainy combo will always stay wet no matter how hot they are, I put them aside on a specific layer
Others are selected one by one (or several if they share same characteristics) and then, intersect them with the temperature combination that are not humid in order to separate them on a new layer. So, the part that was not selected should be made of only humid
climate. When we are done with this, we can put the remaining areas with the always wet layer created earlier.
-Now we know where the desert, steppe and humid climate are. We can separate the cold from the hot arid climate or not because I don't think it's really a big deal.
-Taking the wet climates, we intersect the layer with the temperature groups (A,Ca,Cb...) and create a new layer for each. Or we could just delete the arid part based on the arid layers, but it's the same result.
-When it's done, we still have to figure whether it's summer dry, winter dry or normal. Normal (f) have no dry season and it's when the precipitation for each season is no further than 1 category apart. For example: Category 5: over 200mm and Category 4: 100-200mm.
I made a simple table for this and it's nothing complicated. Winter dry have very low precipitation in their dry season, often lower than the lows of summer dry.
-With these w,s and f layer, we separate the temperature groups into Cfa,Csa.Cwa,Cfb...
Now we have the actual climates
-Some corrections to the map seems inevitable. Some deserts are surrounded by humid climate with no transition. Usually it's because the transition would occur inside the driest precipitation category. But since I'm using the average, there is only one value abd the transition is sometimes impossible. We need to add the steppe generally outside of the desert. I will come back to this later but the process is not perfect and still need some tweeking.
The result, I had to make the map 20% smaller to make it fit:
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