🌧️ Chiba: Rain Warning Thresholds Lowered

❓ What is changing?

On September 29, 2026, the Japan Meteorological Agency (JMA) announced that, because Typhoon No. 25 caused levee breaches on some rivers in Chiba Prefecture, it will operate lowered warning criteria for heavy rain from that day until further notice. Newly covered are Narita City, Inzai City and Sakae Town, where the runoff index criteria are cut to 70% of the normal level. Where levees and embankments are damaged, rivers can hold far less water, so flooding can occur with rainfall that would normally cause no damage. Three products are affected: the Level 4 Heavy Rain Emergency Warning, the Level 3 Heavy Rain Warning and the Level 2 Heavy Rain Advisory. Chiba City and Yachiyo City have already been running provisional criteria at 80% of normal since August 21, and the three new municipalities are now added. With lower thresholds, the same amount of rain will trigger information earlier and at a higher level than before. The provisional criteria are also reflected in the five-color Flood Kikikuru and Heavy Rain Kikikuru risk maps, so residents can keep using them to narrow down which areas should evacuate. The JMA says it will continue checking the state of levees and the relationship between rainfall and disasters, and may revise the criteria as needed.

👥 Who is affected?

• ●Residents and workers in Narita City, Inzai City and Sakae Town, Chiba (newly set at 70%)
• ●Residents and workers in Chiba City and Yachiyo City (80% criteria continuing since Aug 21)
• ●Travelers using Narita Airport or staying at hotels and vacation rentals nearby
• ●People living in houses, apartments or dormitories along rivers or in low-lying areas
• ●Commuters who drive or take buses to logistics centers, farms and factories in these areas

🌏 Impact on foreign residents

The three newly covered municipalities host logistics centers and farms that employ many technical intern trainees, Specified Skilled Workers and international students, and the area around Narita Airport is full of foreign travelers. With lower thresholds, rain that used to stop at an advisory will now trigger a warning or Level 4 information. If you are not used to Japanese disaster alerts, it is easy to dismiss this as an overreaction — but where levees are broken, the risk really is higher. Do not treat it as a false alarm: always check the Kikikuru map colors and your municipality's evacuation information. Ask your employer, school or dormitory manager in advance what the rules are for commuting, going home and evacuating when a warning is issued. Travelers should also expect planned suspensions of trains and buses, which can disrupt access to Narita Airport.