Why it matters. It's a concrete example of how climate change is forcing scientists to rewrite the basic vocabulary they use to describe weather, not just the forecasts themselves.
Background. 'Jangma' is the East Asian summer monsoon as it affects Korea, traditionally running from late June through July and a defining feature of Korean summers. It is a household word tied to flooding, farming and daily life, so changing its scientific definition carries real public and cultural weight. The Korean Meteorological Society is the country's main professional body for atmospheric science, working alongside the government's weather agency (KMA).
What to watch next. Watch whether the Korea Meteorological Agency formally adopts these terms in its official forecasts and whether the rejected 'wet season' label resurfaces as the climate keeps shifting.
A New Definition for a Changing Climate
South Korea’s meteorological community has officially redefined the term jangma — the country’s summer rainy season — after the old definition increasingly failed to match reality. On June 5, the Korean Meteorological Society announced the change, separating the single word into three distinct concepts and broadening what counts as seasonal rain to reflect more erratic, intense and unpredictable summer downpours.
For decades, jangma was defined narrowly as rain produced by a stationary front — the boundary where warm, humid tropical air from the south meets cold, moist polar air from the north. But as Korea’s summers shifted, that definition stopped holding up.
Why the Old Definition Broke Down
Meteorologists say the seasonal rains no longer behave as they once did. The start and end of jangma have grown blurry; declaring it “begun” no longer guarantees continuous rain; and heavy downpours now strike outside the traditional window. The season has also become wildly inconsistent year to year — unusually short in some years, yet record-breakingly long in 2020.
Most strikingly, localized cloudbursts dumping more than 100mm of rain per hour — once rare in Korea — have become far more common. These shifts fueled calls to rethink the concept entirely.
What Actually Changed
The society now splits the idea into three terms:
- Jangma follows the standard dictionary meaning: “a phenomenon or weather pattern in which rain falls for many consecutive days in summer.”
- Jangma-cheol (the rainy-season period) is the meteorological concept — the stretch when the North Pacific high expands northward and conditions favor heavy rainfall over the Korean Peninsula.
- Jangma-bi simply means “rain that falls during the rainy season.”
The biggest shift: the rainy season is now defined by the conditions for rain, not whether rain actually falls. In other words, it can be “the rainy season” even during a dry spell. The cause of the rain has also been broadened from “stationary front” to “various mechanisms” — including mid-latitude low-pressure systems and convective storms — though rain from typhoons is excluded. Experts also dropped reference to the Okhotsk Sea high, saying its very existence is unclear.
The Debate Behind the Decision
The revision followed more than two years of discussion led by the government-designated Jangma Specialized Research Center, drawing on expert input and public surveys. Some had pushed to replace jangma with the more universal term “wet season” (ugi), but the society declined. Son Seok-woo, the center’s director and a Seoul National University professor, said the prevailing view was that “replacing the rainy season with ‘wet season’ is premature.”
Kim Cheol-hee, president of the Korean Meteorological Society and a professor at Pusan National University, said the update should “improve scientific understanding of jangma amid a changing climate and ease social communication,” reducing the recurring annual disputes over what the rainy season actually is.
