Taiwan's Climate

30-second overview: Taiwan receives 2,500 mm of rain annually — 2.5 times the global average — yet simultaneously ranks among the world's top 20 water-stressed nations. This contradiction is the first key to understanding Taiwan's climate. The rain is not insufficient; it is too concentrated, too violent, and too quickly gone — just like everything on this island, always extreme.

Too Much Rain, and Still Running Dry

On the same day, it can be 30°C on the Taipei plain, and a two-hour drive toward the Central Mountain Range reveals nine centimeters of snow on Hehuanshan. Taiwan's climate is not merely complex — it is compressed. Nearly every climatic zone found across the earth's major latitude bands is stacked together on this 400-kilometer-long island.

Taiwan's mean annual rainfall is 2,500 mm, but 80% of that falls in the six-month window from May to October.¹ The Central Mountain Range channels rain into the mountains, which then rushes rapidly out to sea — there is no way to hold it. Combined with high population density and water-intensive agriculture, the per-capita freshwater allocation falls far below the global average, forcing Taiwan onto a water-scarcity watchlist alongside desert nations.

This paradox — abundant rain that is nonetheless insufficient — is the core of Taiwan's entire water resource crisis and explains why the drought of 2021 shocked the entire island.

An Anomaly on the Tropic of Cancer

Nearly everywhere the Tropic of Cancer crosses, the landscape is desert or semi-arid: the Sahara, the Arabian Peninsula, northern Mexico. Taiwan, incongruously perched on this line, is lush and dense with life, its species diversity ranking among the world's highest. Three forces conspire to explain this: mountain, sea, and monsoon.

At the island's center stands a spine with more than 100 peaks exceeding 3,000 meters; the highest, Yushan at 3,952 m, is even the tallest mountain near the Tropic of Cancer anywhere in the world.² This mountain ridge intercepts the moisture arriving from the Pacific, forcing it upward, cooling it, and precipitating it as rain. In winter, the northeasterly monsoon sweeps southward from Siberia laden with cold air; meeting the Xueshan Range and Central Mountain Range, it releases itself fully on the windward side at Yilan. By the time it rounds the mountain and reaches Hsinchu, the moisture is exhausted — only accelerated wind remains as it crosses the Taiwan Strait. This is the origin of the folk saying "Hsinchu wind, Yilan rain" (竹風蘭雨) — four characters that capture the magic a landscape works on climate. Yilan records more than 200 rainy days per year, with mountain areas receiving up to 5,500 mm annually; Hsinchu's winter is the windiest in Taiwan, yet almost never sees rain.³

Summer reverses everything: the southwesterly monsoon sweeps northward from the Indian Ocean and South China Sea carrying heat — this time the southwest faces the wind, while Taitung on the eastern side becomes a domain of the warm foehn. Whenever a typhoon crosses, Taitung on the eastern coast often sees foehn temperatures above 40°C — not from direct sunlight, but from hot air being forcibly compressed and descending from the mountains to the west.

✦ "Nearly every climatic zone found across the earth's major latitude bands is stacked together on this 400-kilometer-long island."

The Four Seasons: Not What the Textbooks Say

Taiwan's "four seasons" is a polite description. A more accurate account would be: plum rain, typhoons, the northeasterly monsoon, and a brief winter — four climatic events taking turns in command, with occasional weeks that might be called "spring" or "autumn" inserted between them.

From mid-May to mid-June each year, the plum rain front stalls near Taiwan, delivering sustained rainfall that replenishes reservoirs with a large volume of water. Plum rain accounts for 15–20% of annual precipitation, and agriculture depends on it to irrigate the first rice crop. But the plum rain is an unpredictable supplier — sometimes raining continuously for three weeks, sometimes never arriving at all; the latter, known as a "dry plum rain season" (空梅), is a warning sign of the drought to follow.

July through September is the heart of typhoon season. An average of three to four typhoons strike Taiwan directly each year, delivering rainfall that accounts for 30–40% of annual precipitation. In Taiwan, typhoons are not only a disaster — to some extent they also serve as a "forced replenishment mechanism" for reservoirs. In years without typhoons, reservoir levels often begin falling dangerously by autumn.

From October onward, the northeasterly monsoon takes command, and Taiwan enters a "wet north, dry south" pattern that persists until the following spring. January in Tainan is almost rainless; January in Taipei is grey and drizzly. "Once you cross the Zhuoshui River, the weather is like a different world" is a common perception among people from central Taiwan.

When winter reaches Hehuanshan, snow accumulation can exceed nine centimeters. That same day, the lowlands may still be a clear 15°C winter afternoon. Taiwan's elevation compresses its climatic zones, allowing you to see, on the same island and the same afternoon, a tropical coastline and snow-covered mountains.

Typhoon Morakot: August 8, 2009

In 2009, a few numbers overturned everything previously understood about Taiwan's climate.

The 24-hour cumulative rainfall at the Alishan weather station: 1,403 mm. Taiwan's mean annual rainfall: 2,500 mm. In other words, Alishan received more than half a year's worth of rain in a single day.⁴ During the period Typhoon Morakot was over Taiwan (August 6–10), the total cumulative rainfall at Alishan exceeded 2,884 mm — surpassing Taiwan's mean annual rainfall and approaching world rainfall records.⁵

These numbers are the backdrop. The story lies in the village of Hsiaolin in Jiaxian Township, Kaohsiung County.

1. 2009/08/08 15:30 — Typhoon Morakot's center approaches Taiwan; torrential rain continues
2. 2009/08/09 05:00 — On the northeast side of Hsiaolin Village, Xiandou Mountain, which had not been subject to human development, develops multiple rupture zones after continuous heavy rain
3. 2009/08/09 06:09 — A massive landslide blocks the Nanzi Xian River, forming a barrier lake that immediately collapses
4. 110 seconds later — The flood destroys the eighth and ninth bridges; over 100 households vanish from the map
5. Final count — 491 people missing; the 9th to 18th neighborhoods of Hsiaolin Village are buried under debris⁶

This is not simply a story of human negligence or inadequate disaster prevention. Investigations by The Reporter found that the dip-slope geology of Xiandou Mountain, combined with extensive fracturing of the rock mass caused by Taiwan's vigorous orogenic activity, meant extreme rainfall provided only the final catalyst.⁷ Climate, geology, topography — Taiwan's geographic conditions combined at their worst to produce the most severe typhoon disaster since the Floods of August 7, 1959: 681 deaths, 18 missing.

Curator's note
The most heartbreaking aspect of the Hsiaolin Village event is not the disaster itself, but that the geological conditions of Xiandou Mountain were already there: "There had been previous landslides; a considerable accumulation of loose colluvium had already built up." This mountain was not "destroyed" by Morakot — it simply finally received enough rain. Climate extremity means that the threshold of "not yet enough, not yet collapsing" is being crossed more and more easily.

The Drought of the Century: 2021

In the summer of 2020, the subtropical high-pressure system produced its strongest and most sustained anomaly since 1949. The Pacific high pinned Taiwan down; typhoons skirted around it; the plum rain ended early; summer's replenishment failed entirely.⁸

The following winter, spring rains also failed to arrive on schedule. By spring 2021, Taiwan's major reservoirs had fallen to historic lows. Tsengwen Reservoir held less than 5% of its capacity. The water sources for Hsinchu Science Park (竹科), Taiwan's most important technology hub — Paoshan Reservoir and Paoshan Second Reservoir — were also precarious. 2021 was called the "drought of the century," the most severe drought since complete records began in 1947.⁹

Agriculture was caught in the middle. Tea bushes in Gukeng, Yunlin, could not produce new buds, dramatically reducing the spring tea harvest; green plum production in Taoyuan, Kaohsiung, was estimated to drop by half; agricultural losses across Nantou, Yunlin, and Chiayi added up to more than NT$200 million.¹⁰ The farmers' saying "living off the sky" became a most blunt reality in the spring of 2021.

The situation at Hsinchu Science Park (竹科) was more alarming. Semiconductor manufacturers, including TSMC, are among Taiwan's largest water consumers; the water scarcity put the entire technology industry on edge. The government deployed water tanker trucks to supplement factory water supplies while emergency crop-failure payments were made for more than 50,000 hectares of farmland, redirecting irrigation water to industrial and residential use.

The resolution of the century drought ultimately came through several waves of plum rain front beginning in late May 2021, followed by a typhoon in July. The year's greatest crisis was, once again, ended by climatic events themselves.

Contested perspective
The drought of the century highlighted deep structural contradictions in Taiwan's water resource allocation: agriculture accounts for over 70% of total water usage in Taiwan, yet agriculture is typically the first to be sacrificed in a water shortage crisis. Farmers say "there is no water, but we still need to eat"; industry says "give the water to us and the GDP we create gives back more." The same drought, different parties, different injustices.

The Climate Change Bill

Over the past 100 years, Taiwan's mean temperature has risen approximately 1.6°C — a rate higher than the global average increase over the same period. More troubling is sea level: Taiwan's sea level is rising at twice the global average rate, climbing at 3.4 mm per year over the past 20 years.¹¹ If warming continues, by 2050 approximately 900,000 people in Taiwan may be affected by sea level rise, with around 1,131 square kilometers of land at risk of inundation.

At the same time, in 2022 the U.S. NOAA issued a warning that Taiwan was facing its largest coral bleaching crisis in 20 years. Taiwan's coral reef ecosystems are renowned for their richness, but persistently rising seawater temperatures are causing coral to lose their symbiotic algae, gradually bleaching and dying.¹²

What most concerns meteorologists is the trend toward extremity: wet seasons wetter, dry seasons drier; typhoons may decrease in number but increase in intensity. Events like Morakot — "more than a year's worth of rain in two days" — may become more frequent. The 2021 drought of the century may become the new normal rather than the exception.

Taiwan's meteorological observation history began in 1896, when Japanese officials borrowed a local earth-god temple (福德廟) in Hengchun as a temporary station and set up instruments to take measurements.¹³ The people of that era did not know that these numbers, 130 years later, would become evidence for something still unknown.

Curator's note
Taiwan's climatic paradox ultimately reads like a warning: an island receiving 2.5 times the global average rainfall becomes, because of terrain too steep, population too dense, and too few reservoirs, a place that runs out of water. Then its typhoons drop more rain than the annual average in two days. Then comes a full year where typhoons all swerve away and reservoirs run dry to bare rock. Taiwan's climate is not gentle — it only looks that way most of the time.

References

• Taiwan's annual rainfall is 2.54 times the world average — Central Weather Administration Climate Encyclopedia (primary source)
• Characteristics of drought disasters in Taiwan — Climate Change Disaster Risk Adaptation Platform (primary source)
• Hsiaolin Village — Wikipedia (with index of original news sources)
• That Night: How the Large-Scale Collapse and Compound Disaster Caused the Hsiaolin Village Tragedy — The Reporter
• Historical Extreme Climate Disaster Events in Taiwan — Climate Change Disaster Risk Adaptation Platform (primary source)
• 2021 Taiwan Drought and Water Crisis — Wikipedia
• When the Century Drought Becomes Normal — Our Island (PTS)
• Analysis of Sea Level Rise Impact on Taiwan Under Global Warming — Greenpeace Taiwan
• History of Hengchun Weather Station — Central Weather Administration (primary source)
• Taiwan's Sea Level Rise Twice the Global Average — Environmental Information Center
• Analysis of the Causes of the 2020–2021 Century Drought in Taiwan — Atmospheric Sciences Research and Application Database (academic)
• Tropic of Cancer, Taiwan's highest mountain on the Tropic — Wikipedia