Climate Finder

Copyright Richard Runyan © 2014

Edited by Aaron Smalley for The Guild Companion

"For there to be an As climate type, there will have to be an incredible natural phenomena for such to occur, such as a high elevation mountain range, which causes a "rain shadow" effect."

Climate Finder

Although not exhaustively authoritative, this document can aid in determining a locale's climate. This will only work for a world that is very Earth-like. The year should have 12 months, each month with 29-32 days, each day with twenty-four 3600-second hours. If your world's year is significantly shorter or longer than this, then this document will not work. Likewise, it will not work if the world's day is significantly shorter or longer. The world should also have a summer and a winter season in the temperate zones with an Orbital Obliquity similar to the Earth (22° to 25°). The table below shows what is classified as the summer and winter seasons for the Northern Hemisphere on Earth.

Season Months
Summer April, May, June, July, August, September (183 days)
Winter October, November, December, January, February, March (182 days)

Of course, the seasons for the Southern Hemisphere would be reversed as shown above.

If you use a different calendarial system for your world, simply divide the year as equally as possible into summer and winter seasons, as shown in the table above.

Helpful Data

Although it is not truly needed, it is helpful to have the data as listed below.

  • Mean Annual Precipitation (MAP) in millimeters
  • Mean Annual Temperature (MAT) in °C
  • Mean Monthly Temperature of Hottest Month in °C
  • Mean Monthly Temperature of Coldest Month in °C
  • Number of months Mean Monthly Temperature ≥ 10°C
  • Mean Monthly Precipitation of Driest Month in millimeters
  • Mean Monthly Precipitation of Driest Winter Month in millimeters
  • Mean Monthly Precipitation of Wettest Winter Month in millimeters
  • Mean Monthly Precipitation of Driest Summer Month in millimeters
  • Mean Monthly Precipitation of Wettest Summer Month in millimeters
  • Which Season (summer or winter) does the Driest Month Occur (ONLY Savannahs)
  • Dryness Factor (ONLY B climates and see Dryness Factor below)
  • Elevation of locale in meters (ONLY Highlands)

The reason the data listed above is not truly needed is because you can go through the steps in this climate finder, answering each question as desired. Simply record the answer for each question.

Dryness Factor

This is only needed for the B climate types. You will need the Mean Monthly Precipitation in millimeters for all twelve months, then use the below to calculate the Dryness Factor. MAT = Mean Annual Temperature (in °C).

  • Total the precipitation for each season(summer and winter).
  • Divide the summer precipitation by the Mean Annual Precipitation.
    • If answer is ≥0.7, then Dryness Factor = 2 × MAT + 28.
  • Divide the winter precipitation by the Mean Annual Precipitation.
    • If answer is ≥0.7, then Dryness Factor = 2 × MAT.
  • Otherwise, Dryness Factor = 2 × MAT + 14.

Highlands

  • Is the elevation of the locale ≥ 2300 meters (7546 feet)?
    • If No, go to Polar Section.
    • If Yes, is the Mean Monthly Temperature of the hottest month > 0°C?
      • If No, then climate is HF (Highland Frost or Highland Ice Cap).
      • If Yes, then climate is HT (Highland Tundra).

Polar

  • Is the Mean Monthly Temperature of the hottest month ≤ 10°C?
    • If No, go to Arid Section.
    • If Yes, is the Mean Monthly Temperature of the hottest month > 0°C?
      • If No, then climate is EF (Polar Frost or Polar Ice Cap).
      • If Yes, then climate is ET (Polar Tundra).

Arid

  • Is the Mean Annual Precipitation < (10 × Dryness Factor)?
    • If No, go to Is Tropical? Section.
    • If Yes, continue below.
  • Is the Mean Annual Precipitation < (5 × Dryness Factor)?
    • If No, is the Mean Annual Temperature ≥ 18°C?
      • If No, then climate is BSk (Cool Steppe).
      • If Yes, then climate is BSh (Hot Steppe).
    • If Yes, is the Mean Annual Temperature ≥ 18°C?
      • If No, then climate is BWk (Cool Waste).
      • If Yes, then climate is BWh (Hot Waste).

Is Tropical?

  • Is the Mean Monthly Temperature of the coldest month ≥ 18°C?
    • If No, go to Is Cold? Section.
    • If Yes, go to Tropical Section.

Tropical

  • Is the Mean Monthly Precipitation of the driest month ≥ 60mm?
    • If No, go to next question.
    • If Yes, then climate is Af (Tropical Wet).
  • Is Mean Monthly Precipitation of driest month ≥ (100 × (Mean Annual Precipitation − 25))?
    • If No, go to next question.
    • If Yes, then climate is Am (Tropical Monsoon).
  • In which season does the driest month occur?
    • If Summer, then climate is As (Dry Summer Savannah).
    • If Winter, then climate is Aw (Dry Winter Savannah).

Special Note: Although there are very few As (Dry Summer Savannah) climate regions here on Earth, it does not mean such cannot occur on another world, especially a magical world. See Savannah Climates (As, Aw) below for further information.

Is Cold?

  • Is the Mean Monthly Temperature of the coldest month > −3°C?
    • If No, go to Cold Temperate Section.
    • If Yes, go to Warm Temperate Section.

Cold Temperate

  • If… (MUST meet ALL 3 below):
    • 1) Mean Monthly Precipitation of driest winter month > Mean Monthly Precipitation of driest summer month
      • AND
    • 2) Mean Monthly Precipitation of wettest winter month > (Mean Monthly Precipitation of driest summer month × 3)
      • AND
    • 3) Mean Monthly Precipitation of driest summer month < 40mm
      • If Yes to all 3, then first two letters are Ds, and go to Cold Temperate Summer Type Section.
      • If No, go to next question.
  • If… (MUST meet ALL 2 below):
    • 1) Mean Monthly Precipitation of driest summer month > Mean Monthly Precipitation of driest winter month
      • AND
    • 2) Mean Monthly Precipitation of wettest summer month > (Mean Monthly Precipitation of driest winter month × 10)
      • If Yes to all 2, then first two letters are Dw, and go to Cold Temperate Summer Type Section.
      • If No, then first two letters are Df, and go to Cold Temperate Summer Type Section.

Cold Temperate Summer Type

  • If Mean Monthly Temperature of hottest month ≥ 22°C, third letter is a.
  • If Mean Monthly Temperature of hottest month < 22°C AND (number of months Mean Monthly Temperature ≥ 10°C) is ≥ 4, third letter is b.
  • If (number of months Mean Monthly Temperature ≥ 10°C) is < 4 AND Mean Monthly Temperature of the coldest month ≥ -38°C, third letter is c.
  • Otherwise, third letter is d.

Warm Temperate

  • If… (MUST meet ALL 3 below):
    • 1) Mean Monthly Precipitation of driest winter month > Mean Monthly Precipitation of driest summer month
      • AND
    • 2) Mean Monthly Precipitation of wettest winter month > (Mean Monthly Precipitation of driest summer month × 3)
      • AND
    • 3) Mean Monthly Precipitation of driest summer month < 40mm
      • If Yes to all 3, then first two letters are Cs, and go to Warm Temperate Summer Type Section.
      • If No, go to next question.
  • If… (MUST meet ALL 2 below):
    • 1) Mean Monthly Precipitation of driest summer month > Mean Monthly Precipitation of driest winter month
      • AND
    • 2) Mean Monthly Precipitation of wettest summer month > (Mean Monthly Precipitation of driest winter month × 10)
      • If Yes to all 2, then first two letters are Cw, and go to Warm Temperate Summer Type Section.
      • If No, then first two letters are Cf, and go to Warm Temperate Summer Type Section.

Warm Temperate Summer Type

  • If Mean Monthly Temperature of hottest month > 22°C, third letter is a.
  • If Mean Monthly Temperature of hottest month < 22°C AND (number of months Mean Monthly Temperature ≥ 10°C) is ≥ 4, third letter is b.
  • Otherwise, third letter is c.

Savannah Climates (As, Aw)

Here on Earth, there are no As climate types, except in very small localized regions caused by a "rain shadow" effect due to mountains. The interior southwestern quadrant of the large island of Hawai'i has an As climate due to the trade winds coming from the northeast during the summer months with most, if not all, moisture falling on the northeastern faces of Mauna Kea and Mauna Loa.

Hawaii As Zone

The As indicates that it is the summer season that is the driest. However, this is very unlikely since it is the ITCZ (Inter-Tropical Convergence Zone) which dictates the wet and dry seasons in tropical savannahs. During the summer season in the tropical savannah regions, the ITCZ will be bringing in moisture, thus causing the summer season to be wet. Obversely, during the winter season, the ITCZ will be on the other side of the equator, causing the winter season to be the dry season.

The only other region on Earth that has an As climate (as far as I know) is on the island of Sri Lanka, due to the "rain shadow" effect of its highlands. During the monsoon season in Myanmar and Thailand, the northeastern quadrant of Sri Lanka is an As climate.

Sri Lanka

Thus, although it may not be completely impossible for there to be an As climate type, it is so improbable, it may as well be impossible. For there to be an As climate type, there will have to be an incredible natural phenomena for such to occur, such as a high elevation mountain range, which causes a "rain shadow" effect. Otherwise, you will be required to create a world that is entirely fantastical in nature where the laws of nature do not exist. Also, notice that the As row in the table below is highlighted in red to indicate it is a highly improbable climate type. Not impossible, just highly improbable.

Longer/Shorter Years

Unfortunately, I have no suggestions for a world's year that is significantly longer or shorter than the above listed suggestion of 12 months, with each month having 29-32 days, each day equal to twenty-four 3600-second hours. I am currently working on a method to help in calculating for a year/month/day that are significantly longer/shorter. Until then, the only advice I can give is to research such on your own. Just make sure to use university/science web sites for your information. Wikipedia is not completely reliable, since anyone with an account can change a Wikipedia page. But, you can use the list of References and External Site Links at the bottom of each page (if there are any) for more reliable information. Specifically, look for links to Journal Articles and university/science websites.

Longer/Shorter Days

The only suggestion I can offer here is to remember that the slower the world's rotation (longer day) means that the diurnal temperature range (DTR) will be greater. Obversely, the faster the world's rotation (shorter day) means that the DTR will be smaller. For example, if the Earth rotated once every 36 hours, its DTR may be about 270 to 310 °K instead of its normal 280 to 295 °K. If Earth rotated once every 18 hours, the DTR may only be 285 to 290 °K. Please note that these DTRs have not been calculated and are best guesstimates.

Climate Codes Descriptions

Letters Description Rule
1st 2nd 3rd
A Tropical Tcold ≥ 18°C
f     - rainforest Pdry ≥ 60mm
m     - monsoon Not(Af) & Pdry ≥ 100mm − MAP÷25
s     - savannah, dry summer Not(Af) & Psdry < 100mm − MAP÷25
w     - savannah, dry winter Not(Af) & Pwdry < 100mm − MAP÷25
B Arid MAP < 10 × Pthreshold
W     - waste (desert) MAP < 5 × Pthreshold
S     - steppe MAP ≥ 5 × Pthreshold
h         - hot MAT ≥ 18°C
k         - cold MAT < 18°C
C Temperate Thot ≥ 10°C & 0°C < Tcold < 18°C
s     - dry summer Psdry < 40mm & Psdry < Pwwet ÷ 3
w     - dry winter Pwdry < Pswet ÷ 10
f     - no dry season Not(Cs OR Cw)
a         - hot summer Thot ≥ 22°C
b         - warm summer Not(a) & Tmon10 ≥ 4
c         - cold summer Not(a OR b)
D Cold Thot ≥ 10°C & Tcold ≤ 0°C
s     - dry summer Psdry < 40mm & Psdry < Pwwet ÷ 3
w     - dry winter Pwdry < Pswet ÷ 10
f     - no dry season Not(Ds OR Dw)
a         - hot summer Thot ≥ 22°C
b         - warm summer Not(a) & Tmon10 ≥ 4
c         - cold summer Not(a OR b OR d)
d         - severely cold winter Not(a OR b) & Tcold < −38°C
E Polar Climate Thot < 10°C
T     - tundra Thot > 0°C
F     - frost Thot ≤ 0°C
H Highland elevation ≥ 2300 meters
T     - tundra Thot > 0°C
F     - frost Thot ≤ 0°C

Climate Codes Descriptions Table Notes

  • Highland climate is a new climate class that uses the same rules as Polar Climate, except elevation is the primary rule. It has yet to gain full acceptance, but it is slowly being accepted by most climatologists.
  • Tcold = temperature of the coldest month
  • Thot temperature of the hottest month
  • Tmon10 = number of months above 10°C
  • MAT = mean annual temperature
  • Pdry = precipitation of the driest month
  • Pthreshold = precipitation threshold, which varies according to the following rules:
    • if 70% of MAP occurs in winter, then Pthreshold = 2 × MAT
    • if 70% of MAP occurs in summer, then Pthreshold = 2 × MAT + 28
    • otherwise Pthreshold 2 × MAT + 14
  • Psdry = precipitation of the driest summer month
  • Pwdry = precipitation of the driest winter month
  • Pwwet = precipitation of the wettest winter month
  • Pswet = precipitation of the wettest summer month
  • MAP = mean annual precipitation

Climate Color Codes for Cartography

Notes: Hover cursor over a table row and it will be highlighted. The colors listed below are only a suggestion. Whatever color schema you choose is your choice. Color Codes are listed in RGB (0 to 255), CMYK (0% to 100%), and HTML hexicode values.

Climate
Code		 Color (RGB) Color (CMYK) Color
Hexicode		 Color
Example
R G B C M Y K
Af 0 51 0 80 51 89 66 003300  
Am 0 102 0 88 34 100 28 006600  
As 0 153 0 84 13 100 3 009900  
Aw 0 204 0 73 0 100 0 00cc00  
BWh 204 0 0 13 100 100 4 cc0000  
BWk 153 0 0 24 100 100 25 990000  
BSh 204 153 0 21 39 100 1 cc9900  
BSk 153 102 0 33 57 100 18 996600  
Cfa 0 255 0 63 0 100 0 00ff00  
Cfb 102 255 102 50 0 90 0 66ff66  
Cfc 153 255 153 37 0 59 0 99ff99  
Csa 255 140 0 0 55 100 0 ff8c00  
Csb 255 174 0 0 36 100 0 ffae00  
Csc 255 207 0 1 17 99 0 ffcf00  
Cwa 102 255 140 49 0 69 0 66ff8c  
Cwb 102 255 174 47 0 51 0 66ffae  
Cwc 102 255 207 45 0 33 0 66ffcf  
Dfa 0 0 153 100 98 5 6 000099  
Dfb 0 0 204 93 86 0 0 0000cc  
Dfc 0 0 255 88 77 0 0 0000ff  
Dfd 51 51 255 83 74 0 0 3333ff  
Dsa 102 0 255 75 78 0 0 6600ff  
Dsb 153 0 255 62 80 0 0 9900ff  
Dsc 204 0 255 45 82 0 0 cc00ff  
Dsd 255 0 255 27 82 0 0 ff00ff  
Dwa 0 102 255 81 61 0 0 0066ff  
Dwb 0 153 255 70 34 0 0 0099ff  
Dwc 0 204 255 63 0 0 0 00ccff  
Dwd 0 255 255 52 0 13 0 00ffff  
ET 204 204 204 19 15 16 0 cccccc  
EF 255 255 255 0 0 0 0 ffffff  
HT 153 153 51 43 29 100 5 999933  
HF 204 204 102 23 10 75 0 cccc66  

Universal Temperature Codes

Although not used or accepted extensively, some climatologists do use the below thermal codes to add a final pair of letters to the climate codes. These letter codes will replace the third letter for the BS, BW, C, and D climates.

Example: Where I used to live in Wilmington, NC is classified as a Cfa climate type. Using the below, this would be changed to Cfhl, indicating very hot summers and mild winters.

Example: When I lived in Albuquerque, NM is classified as a BSk climate type. Using the below, this would be changed to BShk, indicating very hot summers and cool winters.

Notice, the above climate classification system does not use the Universal Thermal Code system since it is still too new and has yet to actually be implemented. Below is the most current (as of 2010) definition of this thermal code system.

Code Description Mean Average
Celsius Range		 Mean Average
Farenheit Range		 Season C & D Climate
3rd Letter
(avg.)
Min Max Min Max Summer Winter
i severely hot ≥ 35 ≥ 95 summers
h very hot 28 34.9 82.4 94.8
a hot 23 27.9 73.4 82.2 a
b warm 18 22.9 64.4 73.2 b
l mild 10 17.9 50 64.2 winters c
k cool 0.1 9.9 32.2 49.8 a
o cold -9.9 0 14.2 32 b
c very cold -24.9 -10 -12.8 14 c
d severely cold -39.9 -25 -39.8 -13 d
e excessively cold ≤ -40 ≤ -40

Flowchart

Small Climate Finder Image

References

"Köppen climate classification." 01 December 2010. Wikipedia. 11 December 2010 (http://en.wikipedia.org/wiki/Köppen_climate_classification). Only used as portal to two below PDF documents.

Kottek, M., J. Grieser, C. Beck, B. Rudolf, and F. Rubel (2006). "World Map of the Köppen-Geiger climate classification updated". 11 December 2010 (http://koppen-geiger.vu-wien.ac.at/pdf/kottek_et_al_2006_A4.pdf).

Peel, M. C. and B. L. Finlayson and T. A. McMahon (2007). "Updated world map of the Köppen-Geiger climate classification". 11 December 2010 (http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf).

McKnight, Tom L. and Darrel Hess. "Climate Zones and Types". Physical Geography: A Landscape Appreciation. Ninth Edition. Pages 210-259. Upper Saddle River, NJ: Pearson Prentice Hall, 2008. ISBN: 0-13-223901-9.

The Weatherbase. Online Database. (http://www.weatherbase.com/).

International Panel on Climate Change (IPCC). Website and Online Data Distribution Center. (http://www.ipcc.org/ & http://www.ipcc-data.org/maps/).

NASA-JPL. Climate Change.

NOAA. Climate Center.

NOAA. National Climatic Data Center.