East Asia: Annual rainy season underway in the region through at least August

East Asia's annual rainy season will continue through at least August, increasing the risk of regional flooding and landslides/mudslides. The rainy season typically begins in May in eastern mainland China, Taiwan, and Okinawa Prefecture in Japan. Its effects gradually spread to the north and east, encompassing the entire region, including the rest of China, the rest of Japan, North Korea, South Korea, and Russia's Primorsky Kray by mid-June through at least August.

Heavy downpours, flooding, and landslides could affect business, transport, and utility services across East Asia throughout the rainy season. Localized disruptions could persist well after hazardous events have concluded; it could take days or weeks for floodwaters to subside and for authorities to clear landslide debris. Rural communities and informal settlements often suffer the greatest damage and casualties during such events due to poor infrastructure.

This potential for flooding is highest in low-lying communities near watercourses in recognized floodplains. Rivers such as the Heilongjiang, Huaihe, Liaohe, Pearl, Songhuajiang, Yangtze, Yellow in China, Han, Nakdong, Yeongsan, and Geum in South Korea, Tumen, Yalu, Taedong, and Bukhan in North Korea, and Tone, Isikarin, Sinano, Kitakami, Kiso in Japan as well as their tributaries, could overflow during periods of intense rainfall. Flash floods, which often occur with little to no warning, can threaten communities downstream of major rivers or dams in the event of infrastructural failure. Urban flooding is possible in areas with poorly maintained or inadequate drainage systems, while storm surges may trigger flooding in coastal areas. Landslides and mudslides are possible in hilly and mountainous regions.

Tropical systems, including tropical depressions, storms, and cyclones, pose an additional threat during the rainy period. Storms associated with the season occasionally form in the North Pacific Ocean, South China Sea, or the Philippine Sea; these weather systems sometimes track over South Asia and can become very destructive. Tropical systems usually prolong or aggravate disruptions already caused by monsoon rainfall.

Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters. In the event of flooding, localized business disruptions may occur in low-lying areas; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.

The threat of disease outbreaks during the monsoon season cannot be discounted. Backflow from drains mixed with floodwaters can become trapped in open areas when inundations recede. These stagnant pools often become a breeding ground for mosquitoes and bacteria, increasing insect- and waterborne diseases. Exposure to contaminated water from inundated industrial sites, sewer systems, and septic tanks also poses a significant health threat.