East Asia: Annual rainy season underway in the region through at least August /update 1

Event

East Asia's annual rainy season will continue through at least August, bringing an elevated potential for flooding and landslides/mudslides regionwide. The rainy season typically begins to impact eastern mainland China, Taiwan, and Okinawa Prefecture in Japan, in May. 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. The rainy season occasionally deviates from this range due to complex interactions with the atmosphere, regional oceans/seas, and landmasses.

Hazardous Conditions
Heavy downpours, flooding, and landslides could affect business, transport, and utility services across East Asia throughout the 2023 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 their banks 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 areas.

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.

Transport
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.

Health
The threat of disease outbreaks cannot be discounted during the monsoon season. 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.

Advice

Monitor local media for updates and advisories on weather conditions. Confirm all transport reservations (air, ground, and maritime) prior to travel. Make allowances for possible supply chain disruptions throughout the rainy season, particularly in areas affected by flooding and or/landslide events.

Avoid low-lying areas near streams, rivers, and other bodies of water, such as reservoirs and coastlines, due to the threat of flooding. Do not drive on flooded roads. Exercise caution in elevated terrain due to the threat of landslides and mudslides. Charge battery-powered devices when electricity is available; restrict the use of cellphones to emergencies only during periods of severe weather. Take precautions against insect- and waterborne diseases. Keep any necessary medications in a waterproof container.

Resources

China Meteorological Administration
Japan Meteorological Agency