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

[Charerg]

I ended up messing around with writing a GIMP plug-in in Python and updated my old climate script. The new version is largely adopted from Azure's script and works in a similar fashion: the plug-in processes the source maps on a pixel-by-pixel basis. Since this one uses many of GIMP's in-built functions, it's not as efficient as Azure's script, and the processing time is quite long. On the other hand, it now has a nice progress bar that shows how far along the script is from completing. While this is a GIMP plug-in, I'm not 100% sure that it works without installing Python. Anyway, here are the instructions:

Installation:
Place the plug-in in the appropriate folder (usually /Program Files/GIMP 2/lib/gimp/2.0/plug-ins). If uncertain, you can check Edit->Preferences->Folders->Plug-ins to see where the plug-ins are stored. Once in the right folder, the plug-in should be available (you can use Filters->Script-Fu->Refresh Scripts so you don't have to restart GIMP). You should now have the script available under the Image tab:

Activation.PNG

Restrictions for using the script:
- This has been written for and tested in GIMP 2.10
- The image needs to be RGBA (RGB with an Alpha channel) with 8-bit Integer precision

Layer naming restrictions:
The temperature/precipitation layers need to have exactly the following names (the script searches for them by name):

JanTemp
JulTemp
JanPrec
JulPrec

Layer colouring restrictions:
The temperature and precipitation categories need to have exactly the following colours (with the ocean tiles coloured in a separate colour, not transparent as in prior versions of the script):

Temperature zones:

 

Temp Category	R	G	B
Severely Hot	160	0	65
Very Hot	210	60	80
Hot	245	110	65
Warm	250	175	95
Mild	255	225	140
Cool	230	245	150
Cold	170	220	165
Very Cold	100	195	165
Severely Cold	50	135	190
Deadly Cold	95	80	160

The temperature zones in a slider:
TempSlider.png

Precipitation zones:

 

Prec Category	R	G	B
200+ mm	210	200	250
100-200 mm	190	170	240
50-100 mm	150	130	220
25-50 mm	90	80	160
10-25 mm	240	235	160
0-10 mm	235	0	140

The precipitation zones in a slider:
PrecSliderAzel.png

Ocean tiles:

 

R	G	B
155	205	230

Sample Map:
Here is a sample climate map using source maps generated from WorldClim's 1970-2000 dataset:

Source maps:

 

JanPrec.png

JulPrec.png

JanTemp.png

JulTemp.png

Generated climates:
GenClimates.png

The plug-in can be found in the attachments. Feel free to provide any feedback if you have trouble using it. Note that the new script has been set up not to generate any Cc climates, and uses a gradual aridity threshold (unlike the previous versions, which used a stepped threshold as in most publications of Köppen maps).


Update (28/10/20):
- Now supports off-colour pixels (they are assumed to have 0 °C temperature and 1,0 mm precipitation)
- Fixed a bug where the script could paint the ocean in the wrong colour if opacity was set at less than 100%

Big thanks to Coggleton for reporting the issues with the script, this update should solve the problems related to off-colour pixels.

[Coggleton]

Restrictions for using the script:
- This has been written for and tested in GIMP 2.10
- The image needs to be RGBA (RGB with an Alpha channel) with 8-bit Integer precision
---
The temperature and precipitation categories need to have exactly the following colours (with the ocean tiles coloured in a separate colour, not transparent as in prior versions of the script):

Thanks - this looks like it will be quite helpful for me! One question- you mention the various colors need exact RGB values. What about the L,C, and h values? I'm not too familiar with GIMP and other color values besides RGB, so this might just be my ignorance showing.

[Charerg]

Thanks - this looks like it will be quite helpful for me! One question- you mention the various colors need exact RGB values. What about the L,C, and h values? I'm not too familiar with GIMP and other color values besides RGB, so this might just be my ignorance showing.

LCH (and HSV) are only alternative ways of defining a colour. If you change the Hue or Saturation for example, the program adjusts RGB values accordingly.

[Josh Foreman]

Feel free to provide any feedback if you have trouble using it. Note that the new script has been set up not to generate any Cc climates, and uses a gradual aridity threshold (unlike the previous versions, which used a stepped threshold as in most publications of Köppen maps).

First of all, THANK YOU for making this! This is exactly what I was hoping someone would develop. Second of all, I'm well versed in Photoshop, but never used GIMP before, and I'm having problems with some of the basics of your instructions, which I feel like must have been a continuing and evolving conversation spread over these 50-something pages. Is there a post I can search for that might help with the basics? Such as: How to make sure my image is RGBA? (I added an Alpha Channel, but I'm not sure if that's what does it?) What kind of image should my source be? Black continent with white water? Land on a separate layer? When you say the layers have to be specific colors do you mean a layer that's completely filled with that RGB? I was able to run the script, but it was looking for layers that weren't there. I feel like I'm close, but missing something fundamental. Thanks for any help you can provide!

[Charerg]

First of all, THANK YOU for making this! This is exactly what I was hoping someone would develop. Second of all, I'm well versed in Photoshop, but never used GIMP before, and I'm having problems with some of the basics of your instructions, which I feel like must have been a continuing and evolving conversation spread over these 50-something pages. Is there a post I can search for that might help with the basics? Such as: How to make sure my image is RGBA? (I added an Alpha Channel, but I'm not sure if that's what does it?) What kind of image should my source be? Black continent with white water? Land on a separate layer? When you say the layers have to be specific colors do you mean a layer that's completely filled with that RGB? I was able to run the script, but it was looking for layers that weren't there. I feel like I'm close, but missing something fundamental. Thanks for any help you can provide!

If all of the source layers (JanTemp, JanPrec, JulTemp and JulPrec) have an alpha channel, you should be good to go. You can see if a layer has an alpha channel by looking at the layers tab, layers without an alpha channel have their names bolded:

alpha_vs_non-alpha.PNG

To see how the source maps should look like, take a look at the "sample map" section of the instructions in my prior post. You can also test the script using the source maps provided in that section: all you need are those four layers and you should be able to activate the script succesfully and produce the climate map.

[Josh Foreman]

To see how the source maps should look like, take a look at the "sample map" section of the instructions in my prior post.

Ah, maybe I'm misunderstanding what this plugin is actually meant to be accomplishing. I thought it would take a fictional world map I've made and determine Koppen climate zones. But based on the WorldClim's 1970-2000 dataset inputs you've got there, I'm guessing the colors are driving the data for your plugin? And I don't know how to generate those colors on my fictional planet except by vague, under-educated guesses. Do you know of any resources to help me with that part that must come before using your plugin?

[Charerg]

Ah, maybe I'm misunderstanding what this plugin is actually meant to be accomplishing. I thought it would take a fictional world map I've made and determine Koppen climate zones. But based on the WorldClim's 1970-2000 dataset inputs you've got there, I'm guessing the colors are driving the data for your plugin? And I don't know how to generate those colors on my fictional planet except by vague, under-educated guesses. Do you know of any resources to help me with that part that must come before using your plugin?

Yes, namely this tutorial. The first post on the first page has links to all the different sections (figuring out oceanic currents, wind patterns, temperatures and precipitations for a fictional world). Only the last part (generating the climates) is automated .

[Josh Foreman]

Only the last part (generating the climates) is automated .

I see. THanks for clarifying. And if you're taking requests.... make a Python script that does all that other stuff too!

[Charerg]

I see. THanks for clarifying. And if you're taking requests.... make a Python script that does all that other stuff too!

There have been some efforts along those lines, mostly from AzureWings. But that's a much greater undertaking than just taking in the temp and precip data and churning out the climates. Myself, I haven't made any serious attemps at creating a script that could arrive at a plausible temperature or precipitation map from just a land-ocean map as input (or even a DEM). But considering that you'd essentially have to create a simplified climate simulator, more-or-less, with maybe some user-fed parameters (like how warm the planet is relative to Earth), the processing time could become an issue pretty quickly (even my most recent script takes quite long to go through a map).