info-canicule/scripts/build-normales.mjs

#!/usr/bin/env node
// Calcule les normales mensuelles TN / TX par département sur la période WMO 1991-2020
// à partir des données quotidiennes Météo France (Q_<DEPT>_previous-1950-2024_RR-T-Vent.csv.gz).
//
// Output : src/data/normales.json
//   { "01": [{ month:1, tn:-1.5, tx:5.2, tnStd:3.1, txStd:4.2, n:1234 }, ..., 12], "02": [...], ... }
//
// Lancé manuellement (très long : 96 × ~4 MB download + parse).
// À relancer une fois par an, ou jamais — les normales 1991-2020 restent la référence WMO standard.

import { gunzipSync } from 'node:zlib';
import { writeFileSync, mkdirSync } from 'node:fs';
import { dirname, resolve } from 'node:path';
import { fileURLToPath } from 'node:url';

const __dirname = dirname(fileURLToPath(import.meta.url));
const OUT = resolve(__dirname, '../src/data/normales.json');
const BASE = 'https://object.files.data.gouv.fr/meteofrance/data/synchro_ftp/BASE/QUOT';
const PERIOD_START = 1991;
const PERIOD_END = 2020;

const DEPTS = [
  '01','02','03','04','05','06','07','08','09','10',
  '11','12','13','14','15','16','17','18','19','21',
  '22','23','24','25','26','27','28','29','2A','2B',
  '30','31','32','33','34','35','36','37','38','39',
  '40','41','42','43','44','45','46','47','48','49',
  '50','51','52','53','54','55','56','57','58','59',
  '60','61','62','63','64','65','66','67','68','69',
  '70','71','72','73','74','75','76','77','78','79',
  '80','81','82','83','84','85','86','87','88','89',
  '90','91','92','93','94','95',
];

async function fetchAndParse(dept) {
  // Météo France utilise "20" pour la Corse historique (avant split 2A/2B en 1976).
  // On affecte la même normale à 2A et 2B (climat sensiblement homogène à l'échelle mensuelle).
  const fileCode = (dept === '2A' || dept === '2B') ? '20' : dept;
  const url = `${BASE}/Q_${fileCode}_previous-1950-2024_RR-T-Vent.csv.gz`;
  const res = await fetch(url);
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  const buf = Buffer.from(await res.arrayBuffer());
  const text = gunzipSync(buf).toString('utf-8');
  const lines = text.split('\n');
  if (lines.length < 2) return null;
  const header = lines[0].split(';');
  const idxDate = header.indexOf('AAAAMMJJ');
  const idxTN = header.indexOf('TN');
  const idxTX = header.indexOf('TX');
  if (idxDate === -1) return null;

  const acc = Array.from({ length: 12 }, () => ({
    tnSum: 0, tnSquares: 0, tnN: 0,
    txSum: 0, txSquares: 0, txN: 0,
  }));

  for (let i = 1; i < lines.length; i++) {
    const line = lines[i];
    if (!line) continue;
    const cols = line.split(';');
    const raw = cols[idxDate];
    if (!raw || raw.length !== 8) continue;
    const year = parseInt(raw.slice(0, 4), 10);
    if (year < PERIOD_START || year > PERIOD_END) continue;
    const m = parseInt(raw.slice(4, 6), 10) - 1;
    if (m < 0 || m > 11) continue;
    if (idxTN !== -1 && cols[idxTN]) {
      const v = parseFloat(cols[idxTN].replace(',', '.'));
      if (Number.isFinite(v)) {
        acc[m].tnSum += v; acc[m].tnSquares += v * v; acc[m].tnN++;
      }
    }
    if (idxTX !== -1 && cols[idxTX]) {
      const v = parseFloat(cols[idxTX].replace(',', '.'));
      if (Number.isFinite(v)) {
        acc[m].txSum += v; acc[m].txSquares += v * v; acc[m].txN++;
      }
    }
  }

  return acc.map((a, m) => {
    const tnMean = a.tnN > 0 ? a.tnSum / a.tnN : null;
    const txMean = a.txN > 0 ? a.txSum / a.txN : null;
    const tnVar = a.tnN > 1 && tnMean !== null ? (a.tnSquares - a.tnN * tnMean * tnMean) / (a.tnN - 1) : 0;
    const txVar = a.txN > 1 && txMean !== null ? (a.txSquares - a.txN * txMean * txMean) / (a.txN - 1) : 0;
    return {
      month: m + 1,
      tn: tnMean !== null ? +tnMean.toFixed(2) : null,
      tx: txMean !== null ? +txMean.toFixed(2) : null,
      tnStd: +Math.sqrt(Math.max(0, tnVar)).toFixed(2),
      txStd: +Math.sqrt(Math.max(0, txVar)).toFixed(2),
      n: Math.min(a.tnN, a.txN),
    };
  });
}

const start = Date.now();
const all = {};
let done = 0;
for (const dept of DEPTS) {
  const t0 = Date.now();
  process.stdout.write(`[${++done}/${DEPTS.length}] ${dept}... `);
  try {
    const r = await fetchAndParse(dept);
    all[dept] = r;
    console.log(`ok ${(Date.now() - t0) / 1000 | 0}s`);
  } catch (e) {
    console.log(`FAIL ${e.message}`);
    all[dept] = null;
  }
}

mkdirSync(dirname(OUT), { recursive: true });
writeFileSync(OUT, JSON.stringify(all));
const dur = ((Date.now() - start) / 1000 / 60).toFixed(1);
const size = (JSON.stringify(all).length / 1024).toFixed(1);
console.log(`\nWrote ${OUT} (${size} KB) in ${dur} min`);