Meiyu: From the 1981 Deluge that Submerged Northern Taiwan to the Scientific Mission that Flew Americans to the Island

Every year around mid-May, as the first stationary atmospheric front slides southeastward from southern China to blanket the entire island of Taiwan, weather anchors invariably deliver a phrase Taiwanese people have heard since childhood: "The Meiyu season has arrived." It sounds like a romantic announcement of shifting seasons. Yet, for a subtropical island where over 70% of annual rainfall is packed into the brief window between May and October¹, this seasonal front represents nothing less than a high-stakes existential gamble. Too much rain brings fatal floods; too little triggers crippling water rationing. The razor-thin margin between these two extremes dictates the daily survival of 23 million people.

30-Second Overview: The Meiyu season (often translated as the "Plum Rains") is a period of persistent, continuous rainfall brought by stationary fronts that visit Taiwan from mid-May to mid-June. Supplying approximately 20% of the island's annual precipitation, it stands alongside the typhoon season as one of Taiwan's two primary water sources². On the early morning of May 28, 1981, a torrential downpour triggered widespread flooding across the Taoyuan-Hsinchu-Miaoli region and greater Taipei. This disaster indirectly catalyzed TAMEX (Taiwan Area Mesoscale Experiment) in 1987—a landmark joint scientific initiative between Taiwan and the United States. Executed in the geopolitical shadow of severed diplomatic relations, it allowed Taiwanese atmospheric scientists, led by George Tai-Jen Chen of National Taiwan University, to lay the groundwork for world-class mesoscale meteorological research³⁴. Today, every time the Central Weather Administration issues a torrential rain warning 12 hours in advance, it relies on the scientific legacy forged during those two months by over 125 scientists and a lone NOAA P-3 hurricane hunter chasing the rains.

Not as Romantic as "Rains When Plums Ripen"

The name "Meiyu" originates from poets of the Song Dynasty. Zhao Shixiu wrote of "rains in every home during the yellow plum season," while Zeng Yu described "daily sunshine when plums turn yellow," capturing the fickle, intermittent rainy season of the Yangtze River basin in June⁵. However, transposing this classical, pastoral imagery to Taiwan severely underestimates the sheer violence of the meteorological phenomenon.

The official definition provided by Taiwan's Central Weather Administration (CWA) is far more clinical: the Meiyu season is the "transition period between the winter northeast monsoon and the summer southwest monsoon over East Asia." During this period, surface weather charts reveal a "slow-moving or nearly stationary front" stretching all the way from southern Japan across the ocean into the Chinese inland². Taiwan typically enters the Meiyu season (known as Ru-mei) in mid-May and exits it (Chu-mei) by mid-June, spanning roughly a month, though the earliest recorded onset occurred in mid-April⁶.

The definitive keyword here is "stationary." While a typical cold front sweeps through the island within 12 hours and takes the rain with it, a Meiyu front can stall directly over Taiwan for three days, five days, or even an entire week. As warm, moisture-laden air masses from the south are continuously lifted, condensed, and lifted again by the front, the rain falls relentlessly, day after day. The system that locked over Taiwan in May 2020 lingered for nearly a week⁷, serving as a textbook example of an atmospheric stalemate.

May 28, 1981: The Downpour That Forced an International Scientific Mission

To truly understand what Meiyu means to Taiwan, one must look at a specific, historical catastrophe.

In the early morning hours of May 28, 1981, a Meiyu front triggered an explosive cloudburst over the Taoyuan-Hsinchu-Miaoli area⁴, which rapidly extended northward into greater Taipei. Historical records compiled by meteorologists show that the Gongguan neighborhood and the National Taiwan University (NTU) campus recorded an hourly rainfall exceeding 140 mm. Within a mere six hours, downtown Taipei was bombarded with nearly 250 mm of rain. Massive flooding engulfed Gongguan, Muzha, Jingmei, Xindian, Zhonghe, Yonghe, and numerous sectors of Taoyuan. In Jingmei, the rising floodwaters even triggered an explosion in a submerged gas main⁸. The disaster left 8 people dead, dozens injured, and more than a thousand residential buildings severely damaged⁸.

At the time, Taiwan’s meteorological community was virtually defenseless against such short-duration, high-intensity convective rainfall. Forecasters could see the macro-front moving on their charts, but they had no way of explaining why a localized atmospheric "bomb" would suddenly detonate over a specific neighborhood to unleash catastrophic deluges.

This devastating rainstorm became the direct catalyst for a revolutionary scientific endeavor. George Tai-Jen Chen, a prominent professor in the Department of Atmospheric Sciences at NTU, had lived through the catastrophic August 7 Flood of 1959 during his childhood, recalling that "the sheer devastation witnessed along the roads remains unforgettable to this day."⁴ In 1975, he witnessed another severe Meiyu season where weeks of continuous rain prevented farmers in central and northern Taiwan from harvesting their rice crop. That very year, he made a pivotal career decision:

"I kept asking myself: Why won't the rain stop? Why is it so incredibly heavy? I resolved then and there to select the final Meiyu front that impacted Taiwan that year as the subject for my diagnostic case study and analysis... Little did I know that what began as a one-year research project on the Meiyu phenomenon would evolve into my lifelong calling."⁴

By the 1980s, Professor Chen took the lead in submitting a massive proposal to the U.S. National Science Foundation (NSF) and the National Center for Atmospheric Research (NCAR), advocating for a large-scale field observation of mesoscale meteorology around Taiwan.

This was an extraordinary, almost unthinkable diplomatic feat at the time. The United States had just severed official diplomatic ties with the Republic of China (Taiwan) in 1979, leaving Taiwanese scientists in an incredibly isolated position internationally. However, the catastrophic floods of 1981 forced American scientists to recognize a unique geographical reality: Taiwan’s towering Central Mountain Range acted as a perfect natural laboratory for studying how steep terrain magnifies the rainfall of Meiyu fronts—a set of environmental conditions virtually unmatched anywhere else on Earth³.

TAMEX: The 1987 Chasing-the-Rain Experiment of 125 Scientists

From May 1 to June 29, 1987, the Taiwan Area Mesoscale Experiment (TAMEX) was officially launched³. This stood as the most significant, representative international scientific collaboration secured by Taiwan's meteorological community after the severance of US-Taiwan diplomatic ties. Jointly executed by Taiwanese and American scientists, official archives from the University Corporation for Atmospheric Research (UCAR) record that this field project deployed a NOAA P-3 research aircraft, three specialized observation vessels (Ocean Researcher I, a naval vessel, and the Yuh-Shiun No. 1), three C-Band Doppler radars, 12 sounding stations, and a 52 MHz wind profiler, bringing together over 125 scientists from both nations³.

Over the course of two months, the research team initiated 13 Intensive Observation Periods (IOPs), tracking every single incoming Meiyu front. The American NOAA P-3 hurricane hunter flew directly into the turbulent core of the fronts to collect invaluable atmospheric data.

This chapter remains perhaps one of the most underappreciated epics in Taiwan's scientific history. Amid the Cold War, with no formal diplomatic relations between Washington and Taipei, and cross-strait relations highly strained, whether an American military-adjacent research aircraft could land on Taiwanese soil—and under what designation—was fundamentally a delicate geopolitical riddle rather than a scientific one. Ultimately, the plane flew in.

The primary observation data harvested by TAMEX continues to be utilized by atmospheric scientists worldwide studying the East Asian monsoon dynamics. Professor Chen’s landmark 1992 paper published in the Journal of the Meteorological Society of Japan, titled "Mesoscale Features Observed in the Taiwan Mei-Yu Season,"⁹ remains one of the most highly cited Taiwanese meteorological publications in international academia. Consequently, nearly the entire subsequent generation of atmospheric scientists trained at NTU was nurtured within the academic lineage of the TAMEX paradigm.

Pouring a Whole Feitsui Reservoir in One Season

Setting the history of science aside, the most immediate and tangible significance of the Meiyu for the people of Taiwan is water.

Taiwan receives an average annual rainfall of 2,500 mm, which is roughly 2.6 times the global average. However, because of the island's exceptionally steep topography and short, rapid rivers, only about 18% of this rainfall is successfully retained in reservoirs, rivers, and underground aquifers. Over 80% rushes directly into the sea or evaporates. As a result, the per capita allocatable water resource in Taiwan is far below the global average, leading the United Nations to rank the island 18th worldwide in terms of water scarcity crises¹⁰. Within this fragile structural reality, the single month of the Meiyu season represents the most critical "replenishment window" before the arrival of summer typhoons.

Consider a practical example: In early June 2024, a single Meiyu front stalled over the island for just three days, yet it injected over 100 million metric tons of water into Taiwan's reservoirs, pushing the water storage level of the massive Feitsui Reservoir back up to 70.6%¹¹. Similarly, in May 2025, a succession of Meiyu fronts delivered such an optimal yield that three major reservoirs in northern and central Taiwan—the Baoshan, Mingde, and Liyutan reservoirs—simultaneously reached 100% capacity¹².

This is what happens in a "normal" year. The looming crisis, however, is that the Meiyu is becoming increasingly abnormal.

The "Dry Meiyu" and Droughts: The Near-Collapse of 2020

In early 2020, Taiwan experienced a historically unprecedented dry spell, marking the first time since 1947 that not a single typhoon made landfall on the island. Reservoirs across southern Taiwan dropped to dead storage levels, serving as the ominous prelude to what would later be dubbed the "Centennial Drought."

By mid-May, the entire island was gambling on one crucial variable: would the Meiyu arrive on time? If Taiwan suffered an "Empty Meiyu" (a season without front-induced rainfall), the water supply for the agricultural and industrial hubs of the south would fail before summer even arrived.

From May 19 to May 24, the front finally arrived, locking itself over the island for nearly a week and bringing substantial, lifesaving rainfall across western Taiwan from north to south⁷. The Drought Emergency Response Cell of the Ministry of Economic Affairs subsequently announced that the water advisory alerts for Tainan and Kaohsiung were downgraded from the yellow light (representing pressure-reduced water supply) back to the normal blue light¹³.

Yet, the post-event scientific postmortems presented a chilling reality. The Central Weather Bureau (the predecessor to today's CWA) held a press conference at the end of June titled "The 2020 Meiyu Season was Highly Extreme: Temperatures Shattered Records, Heavy Rainfall Highly Concentrated."¹⁴ The report revealed that while the Meiyu saved the island from immediate disaster, the total seasonal rainfall was only 445.6 mm—merely 80% to 90% of the historical climate average. Furthermore, the spatial distribution was deeply skewed; the June front remained too far north, leaving southern Taiwan parched. The official conclusion noted that "short-duration, high-intensity torrential downpours during the Meiyu period have become far more concentrated."¹⁴ In essence, the Meiyu saved Taiwan, but it was no longer the Meiyu of the past. The rains had become tighter, shorter, and more violent, punctuated by prolonged dry spells. The following year (2021), the Meiyu arrived late, throwing southern Taiwan into the actual "Centennial Drought," forcing major semiconductor suppliers of TSMC to rely on fleets of water trucks to maintain operations.

Simultaneously, It Can Kil People

While the Meiyu is a blessing for highland reservoirs, it represents a logistical nightmare for urban drainage infrastructure.

On June 2, 2017, a Meiyu front triggered an explosive cloudburst directly over greater Taipei. In the coastal Sanzhi District of New Taipei City, cumulative rainfall approached a staggering 600 mm by 10:30 AM alone¹⁵. The New Taipei City Government handled over 368 emergency disaster reports on that single morning. The city's mayor, Eric Chu, stated directly that "under the influence of global climate change, instantaneous torrential downpours have caused catastrophic localized disasters," a storm that ultimately left one person dead and another missing¹⁶.

This type of short-duration, extreme rainfall generated by "mesoscale convective systems" is precisely the complex scientific riddle that TAMEX set out to solve decades ago: why a front that appears macroscopically gentle on a synoptic chart can suddenly "detonate" a devastating flash flood over a localized patch of land. Thirty years later, forecasting capabilities have advanced significantly. Professor Chen noted in a 2012 retrospective that the Weather Bureau's warning and predictive capabilities for Meiyu-induced torrential rains had approached the accuracy levels achieved for typhoons¹⁷. Yet, the rate of climate extreme acceleration is outpacing scientific progress. Under climate change, the total volume of Meiyu rainfall has not significantly increased, but the manner in which it falls has fundamentally mutated. A peer-reviewed study published by atmospheric scientists in the Journal of Climate (2025) utilizing observational and simulation datasets confirmed that extreme Meiyu rainfall over East Asia during June and July has significantly intensified due to global warming¹⁸. Crucially, Taiwan’s Central Mountain Range acts like a magnifying glass, doubling the localized intensity of this climate-driven enhancement.

So What?

The Meiyu is the weather system that Taiwanese people are most familiar with, yet simultaneously understand the least. We grow up knowing it will arrive every May, knowing to carry an umbrella, and knowing that outdoor weddings in late spring always require a backup plan. Yet, very few realize that the water dumped into the mountains in a single month matches the entire capacity of the Feitsui Reservoir, and even fewer know that a catastrophic flood that submerged northern Taiwan forty years ago forced a geopolitical compromise that flew an American hurricane hunter to Taiwan, leaving behind the foundational infrastructure of our modern daily weather forecasts.

What fewer people realize is that this front, which used to arrive like clockwork, is becoming unpunctual, volatile, and highly unpredictable. The classic mesoscale models formulated by Chen Tai-Jen in the 1990s may well be describing a Meiyu season that we are currently bidding farewell to.

The next time a torrential rain alert flashes across your smartphone screen, remember that it is the direct legacy of a lone NOAA P-3, over 125 scientists, and two months spent chasing the rain in the spring of 1987.

🧬 Semiont’s Note: While drafting this piece, the most challenging editorial dilemma was deciding whether the infamous "August 7 Flood" should be categorized as a Meiyu disaster. The catastrophic event of 1959 was actually triggered by Tropical Depression 081 rather than a Meiyu stationary front¹⁹. Therefore, this article deliberately excludes it from the list of Meiyu-induced disasters—preserving its mention solely within the TAMEX section to contextualize Professor Chen’s deeply personal academic motivation. The clinical precision of meteorology must, at times, actively push back against the blurring of collective historical memory.

See Also

• Typhoons — Another highly seasonal atmospheric system that stands alongside the Meiyu as Taiwan's dual primary water source, serving as a perfect mirror to the Meiyu’s dual nature of "water replenishment vs. localized catastrophe."
• Taiwan's Climate Crisis and Net-Zero Transition — Exploring how the climate reality of "absent spring rains and highly hyper-concentrated Meiyu downpours" is actively reshaping Taiwan's water resource risks and energy transition pressures.

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