Annual rainfall is the wrong number for planning a trip. I pulled five years of monthly precipitation for 311 Chinese cities and asked a different question: how much of the year falls in the two wettest months?
The answer inverts the obvious ranking.
The setup
Beijing: 796 mm per year. Xiamen, on the Fujian coast: 1,572 mm — almost exactly double.
By annual total, Beijing looks safe and Xiamen looks risky. But Beijing takes 35% of its entire annual rain in July alone (280 mm), and 62% across July and August. Xiamen's wettest month is 242 mm, and its two wettest months are only 29% of its year.
One city has a rainy season you can avoid. The other has rain as a standing condition.
How I measured it
Data: Open-Meteo monthly precipitation, 2021–2025, aggregated per city. Filter: cities with at least 500 mm of annual rain — 311 survived.
-- per city: share of annual rain in the two wettest months SELECT city_slug, SUM(rain_mm) AS year, (SELECT SUM(rain_mm) FROM ( SELECT rain_mm FROM city_climate c2 WHERE c2.city_slug = c1.city_slug ORDER BY rain_mm DESC LIMIT 2 )) AS top2 FROM city_climate c1 GROUP BY city_slug HAVING year >= 500; Then top2 / year ranks the cities by concentration.
What came out
| City | Rain / year | Wettest month | Share of year | Two wettest months |
|---|---|---|---|---|
| Baoding | 863 mm | 309 mm (Jul) | 36% | 64% |
| Langfang | 868 mm | 308 mm (Jul) | 35% | 63% |
| Beijing | 796 mm | 280 mm (Jul) | 35% | 62% |
| Tangshan | 895 mm | 273 mm (Jul) | 31% | 60% |
| Xiamen | 1,572 mm | 242 mm (Jun) | 15% | 29% |
| Guangzhou | 1,955 mm | 403 mm (May) | 21% | 38% |
Five of 311 cities put more than 60% of their annual rain into two months. Eighteen clear 55%. Seventy-five stay under 35%.
The top five are all on the north China plain, and all concentrate into July–August. The evenly-rained cities are all southern coastal.
The month count that actually predicts your trip
Count months where rainfall passes 100 mm:
- Beijing: 2 (July, August). Outside those, the city is genuinely dry.
- Shanghai: 6
- Xiamen: 7
- Guangzhou: 7
If you are booking a two-week trip, a city with 7 wet months gives you a reasonable chance of dry weather in almost any month you pick. A city with 2 wet months gives you a binary choice: book July–August and get wet, or book anything else and get dry.
That is actionable. "1,572 mm per year" is not.
What I changed as a result
For the north China plain — Beijing, Tianjin, Hebei — I now treat July and August as a closed season for anything outdoors. Not because the city is wet, but because the fourteen days you would book are drawn from the 62%.
For the south, the rain is not a reason to avoid a month. It is a reason to plan around afternoons: Guangzhou and Xiamen rain hard and briefly, then clear.
The month-by-month table for all 359 cities is free to browse at sinostay — the same dataset behind the when-to-go scoring and the hotel index.
The general lesson
When you aggregate climate (or any real-world series) into a single annual number, you throw away the only thing a traveller can act on: variance. A mean is a summary, and summaries are where products go to die. Publish the distribution, or publish the concentration — but publishing the total is close to publishing nothing.
