How Does Climate Change Affect Changma Precipitation
Will this increase in precipitation be evenly distributed over time?
The answer is no.
There is a change in the characteristics of Changma in frequency and intensity.
For the primary rainy season, from 22 June to 1 August, the amount of rainfall in the post-2000 period is greater than that in the pre-2000 period, whereas the number of rainy days remains similar throughout the entire period. This indicates the increase in rainfall in the rainy season is due to more frequent occurrence of heavy rainfall events. The total amount of rainfall with an intensity greater than 30mm/h, defined as extreme precipitation that may cause flash floods, increased by 52% during the Changma period over the 60 years. The frequency of the extreme rainfall exceeding 30 mm/h presents a slight increase during this period.
extreme (>30 mm) hourly rainfall during JJAS (light colours) and Changma (dark colours) averaged for South Korea stations from 1961 to 2020
(Do et al.,2023)
How will hourly extreme rainfall increase due to Climate Change?
It is clear that Changma season is not only characterized by widespread steady rainfall, but it also frequently brings heavy, localized downpours and extreme rainfall events. Therefore, extreme rainfall events are one of the key characteristics of Changma.
To understand the impact of climate change on summertime hourly extreme rainfall (HER) events over South Korea, a comparison was made between historical (2001-2005) and future periods (2091-2095) under two scenarios of low emissions(SSP1-2.6), high emissions(SSP5-8.5). The results show significant increases in future HER frequency and intensity, especially in July.
The frequency increases about 2 times for SSP1-2.6 and about 3.7 times for SSP5-8.5 scenarios. For the intensity, future projections show high precipitation amounts above the 99.90th percentile, with increases of about 14% under SSP1-2.6 and 60% under SSP5-8.5 compared to the historical period. Overall, the future projection models show that climate change will substantially increase extreme rainfall frequency and intensity, confirming the fundamental shift in the Changma's hazardous characteristics.
* 99.90th percentile: an extreme rainfall event that only occurs 0.1% of the time over a specified historical period (approx. 30.0mm)
Spatial distribution of HER frequency at each ASOS station in July
(Seo et al.,2025)