OCTOBER 19, 2024 — In 2011, a 9.0 magnitude earthquake struck Japan, triggering a devastating tsunami and leading to significant loss of life in the Tōhoku region. Among those affected, the death rate for hearing-impaired individuals in the coastal prefectures of Iwate, Miyagi, and Fukushima was double that of those without hearing disabilities, highlighting a critical gap in tsunami warning communication, particularly for those who could not rely on auditory signals.
In response, discussions began about developing a visual method to effectively communicate tsunami warnings. The Japan Meteorological Agency (JMA) formed a “Study Group on Visual Communication of Tsunami Warnings, etc.” from October 2019 to February 2020. The group included experts from academia, representatives from organizations for the hearing impaired, and communication specialists. Their goal was to design a highly visible tsunami warning flag that would be accessible to a broad range of people, including those with hearing impairments, foreign nationals, and individuals with varying color vision.
The study group recommended a red-and-white checkered flag for tsunami warnings. This design is highly visible, less affected by color vision differences, and not easily confused with other beach flags, such as the “No Swimming” flag. The choice of red and white also aligns with international standards, particularly resembling the “U flag,” an international signal flag that signifies danger. There are no strict size requirements for the tsunami flag, but the short side of the flag should be at least 100 centimeters (approximately 3.28 feet) long to ensure visibility over a distance. The specific shade of red for the flag were also not strictly defined.

In June 2020, based on the study group’s findings, the JMA amended its regulations to officially recognize the red-and-white checkered flag as a visual communication tool for tsunami warnings. While the law does not mandate the use of these flags, it requires local governments to adopt the design if they choose to communicate tsunami warnings visually.
Before the adoption of the checkered tsunami flag, a 2012 survey revealed that local governments used various methods to visually communicate tsunami warnings. Orange flags were the most common, used by 27 municipalities, followed by red rotating lights in 24 municipalities and red flags in 21 municipalities. Six municipalities utilized the U-flag. However, these solutions had limitations, especially for those with color vision deficiencies or foreign nationals unfamiliar with local practices.

A one-year grace period was granted for local governments to transition to the new tsunami flag if they had previously relied on other visual signals. By June 2024, 284 out of 402 local governments with beaches had adopted the red-and-white checkered tsunami flag, representing 71% of those eligible.
It was notably used following the April 3, 2024 earthquake near Taiwan, when a tsunami warning was issued for Okinawa and the surrounding islands. Local authorities in Okinawa raised the tsunami flag as part of their warning system.
Sources:
- 津波フラッグについて – 日本ライフセービング協会
- 津波フラッグ – 気象庁
- 津波警報等の視覚による伝達のあり方(報告書)– 津波警報等の視覚による伝達のあり方検討会
- 「津波フラッグ」による津波警報等の伝達に関するガイドライン – 気象庁
Image: City of Oita official website