302 lines
15 KiB
JavaScript
302 lines
15 KiB
JavaScript
// Köppen climate classification using the "worldbuilding pasta" band-based
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// methodology. Two-season (summer/winter) data is used as a proxy for
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// warmest/coldest month values.
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//
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// Approach:
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// Step 1 – Temperature bands (tropical → temperate → continental → tundra → ice cap)
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// Step 2 – Arid zones (B) dry in both seasons → desert core + steppe fringe
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// Step 3 – Precipitation subtypes within each band (A / C / D details)
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//
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// IMPORTANT: The simulation labels "summer" and "winter" are NH-centric
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// (NH summer = June-Aug, NH winter = Dec-Feb). For each cell we determine
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// the LOCAL warm/cold season from temperature and use that to assign the
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// correct precipitation pattern (s/w/f). Without this, Mediterranean (Cs)
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// and monsoon (Cw/Dw) climates are hemisphere-flipped.
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import { smoothstep } from './wind.js';
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/**
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* Köppen class definitions: ID → { code, name, color [r,g,b] 0-1 }.
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*/
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export const KOPPEN_CLASSES = [
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{ code: 'Ocean', name: 'Ocean', color: [0.29, 0.44, 0.65] }, // #4a6fa5
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{ code: 'Af', name: 'Tropical rainforest', color: [0.00, 0.00, 1.00] }, // #0000FF
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{ code: 'Am', name: 'Tropical monsoon', color: [0.00, 0.47, 1.00] }, // #0077FF
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{ code: 'Aw', name: 'Tropical savanna', color: [0.27, 0.67, 0.98] }, // #46AAFA
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{ code: 'BWh', name: 'Hot desert', color: [1.00, 0.00, 0.00] }, // #FF0000
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{ code: 'BWk', name: 'Cold desert', color: [1.00, 0.59, 0.59] }, // #FF9696
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{ code: 'BSh', name: 'Hot steppe', color: [0.96, 0.65, 0.00] }, // #F5A500
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{ code: 'BSk', name: 'Cold steppe', color: [1.00, 0.86, 0.39] }, // #FFDB63
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{ code: 'Cfa', name: 'Humid subtropical', color: [0.78, 1.00, 0.31] }, // #C8FF50
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{ code: 'Cfb', name: 'Oceanic', color: [0.39, 1.00, 0.31] }, // #64FF50
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{ code: 'Cfc', name: 'Subpolar oceanic', color: [0.20, 0.78, 0.00] }, // #32C800
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{ code: 'Csa', name: 'Hot-summer Mediterranean', color: [1.00, 1.00, 0.00] }, // #FFFF00
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{ code: 'Csb', name: 'Warm-summer Mediterranean', color: [0.78, 0.78, 0.00] }, // #C8C800
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{ code: 'Csc', name: 'Cold-summer Mediterranean', color: [0.59, 0.59, 0.00] }, // #969600
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{ code: 'Cwa', name: 'Humid subtropical (monsoon)', color: [0.59, 1.00, 0.59] }, // #96FF96
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{ code: 'Cwb', name: 'Subtropical highland', color: [0.39, 0.78, 0.39] }, // #63C764
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{ code: 'Cwc', name: 'Cold subtropical highland', color: [0.20, 0.59, 0.20] }, // #329633
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{ code: 'Dfa', name: 'Hot-summer continental', color: [0.00, 1.00, 1.00] }, // #00FFFF
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{ code: 'Dfb', name: 'Warm-summer continental', color: [0.22, 0.78, 1.00] }, // #37C8FF
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{ code: 'Dfc', name: 'Subarctic', color: [0.00, 0.49, 0.49] }, // #007D7D
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{ code: 'Dfd', name: 'Extremely cold subarctic', color: [0.00, 0.27, 0.37] }, // #00465F
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{ code: 'Dsa', name: 'Hot-summer continental (dry summer)', color: [0.90, 0.50, 1.00] }, // #E680FF
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{ code: 'Dsb', name: 'Warm-summer continental (dry summer)', color: [0.70, 0.35, 0.85] }, // #B359D9
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{ code: 'Dsc', name: 'Subarctic (dry summer)', color: [0.50, 0.20, 0.65] }, // #8033A6
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{ code: 'Dsd', name: 'Extremely cold subarctic (dry summer)', color: [0.35, 0.10, 0.45] }, // #591A73
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{ code: 'Dwa', name: 'Hot-summer continental (monsoon)', color: [0.67, 0.69, 1.00] }, // #ABB1FF
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{ code: 'Dwb', name: 'Warm-summer continental (monsoon)', color: [0.43, 0.47, 0.78] }, // #6E77C8
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{ code: 'Dwc', name: 'Subarctic (monsoon)', color: [0.29, 0.31, 0.78] }, // #4A50C8
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{ code: 'Dwd', name: 'Extremely cold subarctic (monsoon)', color: [0.20, 0.00, 0.53] }, // #320087
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{ code: 'ET', name: 'Tundra', color: [0.70, 0.70, 0.70] }, // #B2B2B2
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{ code: 'EF', name: 'Ice cap', color: [0.41, 0.41, 0.41] }, // #686868
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];
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// Lookup table: KOPPEN_CLASSES code → ID (built once at import time)
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const CODE_TO_ID = {};
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KOPPEN_CLASSES.forEach((c, i) => { CODE_TO_ID[c.code] = i; });
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/**
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* Classify each region into a Köppen climate type using the worldbuilding-
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* pasta band-based methodology.
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*
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* @param {object} mesh - SphereMesh
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* @param {Float32Array} r_elevation - per-region elevation (<=0 = ocean)
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* @param {object} tempResult - { r_temperature_summer, r_temperature_winter } (0-1 → -45..+45 C)
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* @param {object} precipResult - { r_precip_summer, r_precip_winter } (0-1 p95-normalized)
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* @returns {Uint8Array} r_koppen - per-region class ID (index into KOPPEN_CLASSES)
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*/
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export function classifyKoppen(mesh, r_elevation, tempResult, precipResult) {
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const n = mesh.numRegions;
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const r_koppen = new Uint8Array(n);
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const tSummer = tempResult.r_temperature_summer;
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const tWinter = tempResult.r_temperature_winter;
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const pSummer = precipResult.r_precip_summer;
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const pWinter = precipResult.r_precip_winter;
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for (let r = 0; r < n; r++) {
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// ── Ocean ──
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if (r_elevation[r] <= 0) {
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r_koppen[r] = 0;
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continue;
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}
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// ── Convert normalised values to physical units ──
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// Ts/Tw are NH summer/winter proxies — NOT necessarily local warm/cold
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const Ts = -45 + Math.max(0, Math.min(1, tSummer[r])) * 90;
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const Tw = -45 + Math.max(0, Math.min(1, tWinter[r])) * 90;
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const Thot = Math.max(Ts, Tw); // warmest month proxy (°C)
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const Tcold = Math.min(Ts, Tw); // coldest month proxy (°C)
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const Tann = (Ts + Tw) / 2;
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// "Shoulder-month" temperature: approximate the temp 2 months before
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// peak summer. With only 2 seasons we interpolate 2/6 of the way from
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// peak toward cold. Used for the humid-continental / subarctic split
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// and for the tempLetter 'b' criterion (4+ months >= 10°C).
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const Tshoulder = Thot - (Thot - Tcold) * (2 / 6);
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// ── Hemisphere-aware local seasons ──
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// Determine which simulation season is this cell's LOCAL warm season.
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// NH cells: sim summer = local summer. SH cells: sim winter = local summer.
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const localSummerIsSim = Ts >= Tw;
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// Precipitation: each season value ∈ [0,1] represents ~6 months.
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// Scale to approximate mm for that half-year.
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const Ps = Math.max(0, pSummer[r]) * 1000; // NH summer half-year mm
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const Pw = Math.max(0, pWinter[r]) * 1000; // NH winter half-year mm
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const Pann = Ps + Pw; // annual mm
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// Local summer/winter precipitation (hemisphere-corrected)
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const PsummerLocal = localSummerIsSim ? Ps : Pw;
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const PwinterLocal = localSummerIsSim ? Pw : Ps;
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const PsMonthLocal = PsummerLocal / 6; // avg monthly precip in local summer
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const PwMonthLocal = PwinterLocal / 6; // avg monthly precip in local winter
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// Estimate driest individual month from the 6-month average.
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// A 6-month dry-season average of 40mm might contain months ranging from
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// 10mm to 70mm. The stronger the seasonal contrast (wet vs dry half-year),
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// the more peaked the distribution within each half-year, so the driest
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// month is further below the half-year average.
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// Factor: at equal seasons (ratio=1) → driest ≈ 0.7× average
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// at strong monsoon (ratio=5+) → driest ≈ 0.35× average
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const seasonRatio = Math.max(PsMonthLocal, PwMonthLocal) / (Math.min(PsMonthLocal, PwMonthLocal) || 1);
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const driestFraction = 0.60 - 0.35 * smoothstep(1, 4, seasonRatio);
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const Pdry = Math.min(PsMonthLocal, PwMonthLocal) * driestFraction;
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// ================================================================
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// STEP 1 – TEMPERATURE BANDS
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// ================================================================
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// Band codes: 'A' tropical, 'C' temperate, 'D' continental,
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// 'ET' tundra, 'EF' ice cap
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// Sub-bands for temperate: 'hotSummer' (>=22°C) vs 'coolSummer'
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// Sub-bands for continental: 'humidCont' (Tshoulder>=10) vs 'subarctic'
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let band;
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let tempSubBand = ''; // 'hotSummer'|'coolSummer' for C; 'humidCont'|'subarctic' for D
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if (Thot < 0) {
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// Ice cap: warmest month < 0°C
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band = 'EF';
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} else if (Thot < 10) {
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// Tundra: warmest month 0-10°C
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band = 'ET';
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} else if (Tcold >= 18) {
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// Tropical: coldest month >= 18°C
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band = 'A';
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} else if (Tcold >= 0) {
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// Temperate: coldest month 0-18°C AND warmest >= 10°C
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band = 'C';
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tempSubBand = Thot >= 22 ? 'hotSummer' : 'coolSummer';
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} else {
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// Continental: coldest month < 0°C AND warmest >= 10°C
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band = 'D';
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tempSubBand = Tshoulder >= 10 ? 'humidCont' : 'subarctic';
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}
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// ── Short-circuit polar types ──
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if (band === 'EF') { r_koppen[r] = CODE_TO_ID['EF']; continue; }
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if (band === 'ET') { r_koppen[r] = CODE_TO_ID['ET']; continue; }
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// ================================================================
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// STEP 2 – ARID ZONES (B)
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// ================================================================
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// The blog approach: areas "dry in both seasons" become desert by
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// default, with steppe as a transition on the edges.
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//
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// We use the standard Köppen aridity threshold (which encodes the
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// idea of evapotranspiration exceeding precipitation) to decide B,
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// then split desert vs steppe.
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//
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// h/k is determined by mean annual temperature (standard Köppen):
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// Tann >= 18°C → hot (h)
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// Tann < 18°C → cold (k)
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//
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// summerFrac uses LOCAL warm-season precipitation (hemisphere-corrected)
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// because the threshold encodes evapotranspiration which peaks in
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// the warm season regardless of hemisphere.
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let Pthresh;
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const summerFrac = Pann > 0 ? PsummerLocal / Pann : 0.5;
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if (summerFrac >= 0.7) {
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Pthresh = 20 * Tann + 280;
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} else if (summerFrac <= 0.3) {
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Pthresh = 20 * Tann;
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} else {
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Pthresh = 20 * Tann + 140;
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}
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Pthresh = Math.max(0, Pthresh);
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if (Pann < Pthresh) {
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const isHot = Tann >= 18; // standard Köppen: h if mean annual temp >= 18°C
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if (Pann < Pthresh * 0.5) {
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// Desert
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r_koppen[r] = isHot ? CODE_TO_ID['BWh'] : CODE_TO_ID['BWk'];
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} else {
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// Steppe (transition fringe)
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r_koppen[r] = isHot ? CODE_TO_ID['BSh'] : CODE_TO_ID['BSk'];
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}
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continue;
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}
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// ================================================================
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// STEP 3 – PRECIPITATION SUBTYPES WITHIN EACH BAND
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// ================================================================
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// ── Determine s / w / f precipitation pattern ──
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// All comparisons use LOCAL summer/winter so the pattern is correct
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// in both hemispheres.
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// Our "monthly" values are 6-month averages, not individual months —
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// this smooths the driest/wettest month contrast, so thresholds are
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// relaxed vs. standard Köppen (which uses actual monthly extremes).
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// s = dry local summer: summer month < 50mm AND < 1/2 winter month
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// w = dry local winter: winter month < 1/4 summer month
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// (relaxed from standard 1/10 because 6-month averages compress contrast)
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// f = no dry season
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let precipPattern;
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const localSummerDrier = PsummerLocal < PwinterLocal;
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if (localSummerDrier && PsMonthLocal < 50 && PsMonthLocal < PwMonthLocal / 2) {
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precipPattern = 's';
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} else if (!localSummerDrier && PwMonthLocal < PsMonthLocal / 3) {
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precipPattern = 'w';
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} else {
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precipPattern = 'f';
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}
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// ── Determine temperature sub-letter (a / b / c / d) ──
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// a: warmest month >= 22°C
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// b: warmest < 22°C but 4+ months >= 10°C (proxy: Tshoulder >= 10°C)
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// c: fewer than 4 months >= 10°C, coldest >= −38°C
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// d: coldest < −38°C (extreme continental, only for D)
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let tempLetter;
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if (Thot >= 22) {
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tempLetter = 'a';
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} else if (Tshoulder >= 10) {
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tempLetter = 'b';
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} else if (Tcold >= -38) {
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tempLetter = 'c';
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} else {
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tempLetter = 'd';
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}
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// ── Band A: Tropical ──
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if (band === 'A') {
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// Blog approach:
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// very wet both seasons → Af (tropical rainforest)
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// wet both seasons → Am (tropical monsoon)
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// wet one season, dry other → Aw (tropical savanna)
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//
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// Translated with thresholds:
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// Af: driest month >= 60 mm
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// Am: Pann >= 25*(100 - Pdry) (i.e. enough total rain to sustain forest
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// despite a short dry spell)
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// Aw: everything else
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if (Pdry >= 60) {
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r_koppen[r] = CODE_TO_ID['Af'];
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} else if (Pann >= 25 * (100 - Pdry)) {
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r_koppen[r] = CODE_TO_ID['Am'];
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} else {
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r_koppen[r] = CODE_TO_ID['Aw'];
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}
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continue;
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}
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// ── Band C: Temperate ──
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if (band === 'C') {
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// Blog approach:
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// dry local summer → Mediterranean (Cs)
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// remaining hot-summer → humid subtropical (Cfa / Cwa)
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// remaining cool-summer → oceanic (Cfb / Cwb / Cfc / Cwc)
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const code = 'C' + precipPattern + tempLetter;
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const id = CODE_TO_ID[code];
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if (id !== undefined) {
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r_koppen[r] = id;
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} else {
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r_koppen[r] = CODE_TO_ID['Cfb'];
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}
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continue;
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}
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// ── Band D: Continental ──
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if (band === 'D') {
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// Blog approach:
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// humid continental (Tshoulder >= 10°C) = Dfa/Dfb/Dsa/Dsb/Dwa/Dwb
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// subarctic (Tshoulder < 10°C) = Dfc/Dfd/Dsc/Dsd/Dwc/Dwd
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//
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// Ds zones appear near Mediterranean regions; Dw zones appear
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// near regions with strong monsoon effect (far ITCZ excursion).
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const code = 'D' + precipPattern + tempLetter;
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const id = CODE_TO_ID[code];
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if (id !== undefined) {
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r_koppen[r] = id;
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} else {
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const fallback = 'Df' + tempLetter;
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r_koppen[r] = CODE_TO_ID[fallback] || CODE_TO_ID['Dfc'];
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}
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continue;
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}
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}
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return r_koppen;
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}
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