The nation has entered the full-fledged rainy season this summer. Following the declaration of the rainy season in Jeju on the 12th, it was also declared in the southern and central regions on the 19th. Jeju’s rainy season began a week earlier than normal, while the southern and central regions started four to six days earlier, marking an 'early rainy season.'

On the afternoon of the 13th, citizens with umbrellas hurry along the road in front of Keimyung University's Seongseo campus in Daegu, avoiding the heavy rain. /Courtesy of News1

◇ In the past, the rainy season during early rainy seasons lasted 5-6 days longer than normal

There was a notable pattern of extended rainy seasons in the years with 'early rainy seasons.' An analysis of historical data from the Korea Meteorological Administration on rainy season start dates from 1973 to 2024 revealed that the average duration of the rainy seasons in years with early rainy seasons was 37.1 days. Among this, the number of days with actual rainfall was reported to be 20.6 days.

This is longer than the normal level. The average rainy season duration and number of rainy days by region were ▲central region 31.5 days (17.7 days) ▲southern region 31.4 days (17 days) ▲Jeju region 32.4 days (17.5 days). An early onset of the rainy season leads to a situation where the rainy season is 5-6 days longer than normal, and the number of rainy days is three days longer.

Of course, past patterns do not necessarily apply to this year's rainy season. A representative from the Korea Meteorological Administration noted, 'The stationary front that brings the rainy season is formed when warm air masses from the south meet cold air from the north. The longer the 'struggle of forces' between the two air masses lasts, the longer the rainy season will be, but whether the stationary front forms early is not directly related to the duration.'

On the morning of July 8th last year, officials and Buddhists at Gaewonsa Temple in Songcheondong, Andong, North Gyeongsang Province, are clearing debris and rocks that fell from the mountainside due to heavy rainfall. /Courtesy of News1

◇ What about this year? A pattern of 'polarization' with extreme rains and heatwaves is likely

It is difficult to predict the appearance of this year's rainy season, but it can be gauged from recent patterns. Firstly, 'extreme rainfall' has been increasing. Last year, strong rains exceeding 100 mm per hour occurred 16 times, the highest since 2010. A representative from the Korea Meteorological Administration explained, 'There is a trend of increasing frequency of heavy rains occurring in a short amount of time.' Countries nearby, such as Japan and Taiwan, which encountered the rainy season earlier than us, also suffered from heavy rainfall within a short period.

The phenomenon of extreme heat following heavy rainfall, termed 'polarization of the rainy season,' is also prominent. A representative from the Korea Meteorological Administration stated, 'The rainy season is expected to transition from the long-known 'period of continuous rain' to a 'polarized' period where heatwaves and heavy rains coexist.'

Meanwhile, according to the Korea Meteorological Administration, strong rains are expected from the evening of Friday the 20th to Saturday the 21st. In particular, heavy rainfall of 30-50 mm per hour has been forecasted, primarily in the central region. Rainfall of over 30 mm per hour means that even with windshield wipers operating at maximum speed, visibility will be significantly reduced. The rain will temporarily ease over the weekend, but it will later spread to the southern region and Jeju at the start of next week, expanding nationwide later in the week.