I was inspired by
QIDb602's thread to make one on my own climate classification system that I created a while back.
TL;DR- basically a mashup of Köppen and Trewartha with a more nuanced precipitation threshold.
The main distinguishing feature or innovation of my system is that the semi-arid and arid climates are automatically assigned to a primary temperature regime (tropical, subtropical, etc.) The second major innovation is temperature-based subcategories for Tropical climates to better distinguish altitude levels and heat regimes.
I think it's important to create a climate classification system centered around human comfort and survivability, especially in a world that is facing rapid and unpredictable climate change in the foreseeable future.
First Letter- primary temperature letter (focused on coldest month). I used 10 C as a threshold for subtropical climates because it's already used to define growth seasons in subpolar and polar climates.
A = Tropical: all months > 18 C
B = Subtropical: all months > 10 C, coldest month < 18 C
C = Temperate: 4-11 months > 10 C, coldest month -3 C to 10 C
D = Continental: > 3 months > 10 C, coldest month < -3 C
E = Subarctic/Subalpine: <= 3 months > 10 C
O = Polar/Alpine: all months < 10 C
OT = Polar Tundra (at least 1 month > 0 C)
OF = Polar Ice Cap (all months < 0 C)
Second Letter- precipitation letter. The dry-summer and dry-winter thresholds are the same as Köppen's. I got the idea to change the tropical rainforest climate threshold from Bisfbath's Af/BSh thread.
For dry climates:
- R = arid (Gk. xeRos): actual precip. less than 0.5 of precip. threshold
- Z = semi-arid (Gk. aZaleos): actual precip. between 0.5-1.0 of precip. threshold
For tropical:
- f = rainforest: different from Köppen (<= 3 months <100 mm, instead of all months >60 mm)
- m = monsoon: same as Köppen (driest month greater than (100-(total/25)) mm)
- w = savanna: same as Köppen (driest month less than (100-(total/25)) mm)
- s = same as above but with summer dry season
For non-tropical:
- s = dry summer: (wettest month > 3 * driest month, driest month < 40 mm)
- w = dry winter: (wettest month > 10 * driest month)
- f = default: no other conditions are fulfilled
Third Letter- secondary temperature (focused on warmest month). I added a third letter for Tropical climates to distinguish between equatorial climates (which have virtually no seasonal temperature variation) and non-equatorial tropical climates, and to distinguish very hot tropical climates (>28 C) like those found in the Asian continent.
For tropical:
- A = very hot: coldest month > 22.5 C AND annual average > 28 C
- e = equatorial: average monthly temp range < 3 C
- E = very hot equatorial: equatorial if annual average > 28 C
- b = cool: annual average < 22.5 C [optional]
- a = default: does not fit any of the other categories
For non-tropical:
- a = hot-summer: hottest month > 22.5 C
- b = warm-summer: hottest month 10 C - 22.5 C
For subpolar/subalpine only:
- b = equatorial: coldest month > 6 C [optional]
- c = maritime: coldest month -3 C to 6 C
- d = continental: coldest month < -3 C
For polar/alpine only [optional]:
- m = mild: coldest month > -3 C
Precipitation threshold: adjusted for average annual temperature and seasonality. The threshold increases faster at higher temperatures due to higher potential evapotranspiration and increased risk of desertification.
Let threshold Q be a function of T and U where T = average annual temperature and U = (sun-high season precip)/(annual precip).
if (T < 10 C) {Q = 100 + 10*T}
else if (T < 20 C) {Q = 200 + 20*(T-10)}
else if (T < 30 C) {Q = 300 + 30*(T-20)}
else {Q = 400 + 40*(T-30)}
if (U < 0.1) {Q += 0}
else if (U < 0.9) {Q += 350*(U-0.1)}
else {Q += 280}
If the threshold Q < 0 then the climate is non-dry by default.
Optional "extreme" designation:
For tropical: >= 6 months average temp > 32 C, must fulfill conditions for third letter A or E
Created with the Red Sea and Persian Gulf regions in mind. Could feasibly appear in South Asia under extreme warming scenarios
For subtropical: >= 3 months average temp > 32 C
Created with the Greater Sahara region and West + South Asia in mind. Could feasibly appear in China under extreme warming scenarios
For subpolar/subalpine: coldest month < -35 C
Created with the Russian Far East in mind, hypothetical category for hyper-continental high-latitude climates
For polar/alpine: coldest month < -50 C, >= 3 months < -40 C
Created with Antarctica in mind, hypothetical category for continental ice sheets
Examples:
London: Cfb
New York City: Cfa
Beijing: Dwa
Dubai: ARa/ARA
Hong Kong: Bwa
Paris: Cfb
Shanghai: Cfa
Singapore: Afe/AfE
Sydney: Bfa
Tokyo: Cfa
Bangkok: AmA/AmE
Istanbul: Csa
Los Angeles: Bsa/BZa
Mexico City: Bwb
Moscow: Dfb
Madrid: Csa
Miami: Awa
Johannesburg: Cwb
Lisbon: Bsa
Montreal: Dfb/Dfa
Riyadh: [xtrm] BRa
Santiago: CZb/Csb
BONUS-
Lima: BRb
Vostok: [xtrm] OF
Yakutsk: [xtrm] Efd
Dallol: [xtrm] ARA
Hyderabad India: Awa/AZa
Hyderabad Pakistan: [xtrm] BRa/ARa