Prevent damage from heavy rain with forecasts on linear precipitation bands

Floods and landslides occur frequently during the rainy season, causing serious damage. It is vital to make effective use of disaster prevention information to prevent damage.

In recent years, attention has focused on “linear precipitation bands” as a cause of heavy rain. This is a phenomenon in which cumulonimbus clouds are generated one after another and cause heavy rain in the same place for a long time. Many deaths occurred during heavy rains in the Kyushu region in July last year, in western Japan in 2018 and other disasters.

The Meteorological Agency said that it will start in mid-June issuing “information on significant heavy rain” regarding linear precipitation bands. Under the system, the agency will quickly capture the conditions of rain clouds and the amount of rainfall, and announce the information if linear precipitation bands are detected.

Due partly to the influence of global warming, heavy rain damage caused by linear precipitation bands is becoming serious. By announcing information similar to that for typhoons, it is hoped that people will be more likely to take swift precautions.

However, the new warning does not include the all-important term “linear precipitation bands.” It is also difficult to distinguish it from the “information about a record-breaking deluge in a short period” warning that has been issued in the past in the event of heavy rain.

It is necessary to consider a concise and easy-to-understand method of disseminating such information.

Linear precipitation bands often occur in western Japan, where warm, moist air flows from the East China Sea and elsewhere. However, the ocean observation system is so weak that it is difficult to accurately predict the movement of rapidly developing cumulonimbus clouds.

Ideally, the system should be able to provide forecasts of weather conditions about half a day in advance. The Meteorological Agency needs to make efforts to strengthen its observation network, through such measures as increasing the number of observation ships, to establish highly accurate forecasts.

It is difficult to convey disaster prevention information. When Typhoon No. 19 hit Japan in 2019, the agency issued a warning, citing the 1958 Kanogawa Typhoon that caused extensive damage to the Tokai and Kanto regions. Some people are said to have misunderstood the warning, believing “other areas would be fine.”

It was also difficult to understand the difference between the “evacuation advisory” that municipalities issued to urge residents to evacuate, and “evacuation instruction,” which is more imminent. For that reason, in May, the central government abolished the “advisory” and merged it into “instruction.”

The more accurate the forecast and the more detailed the information becomes, the more likely it is that people will not run away until instructed. This year, the rainy season started from Kyushu to the Tokai region at an unusually fast pace. Efforts should be made to remain vigilant against heavy rain damage.

It is important to check the degree of danger at home and in the local community with hazard maps on a regular basis, and if necessary, take early evacuation action at your own discretion.

It is also advisable to have flexible plans, such as evacuating to acquaintances’ homes or hotels, in addition to such options as evacuation centers set up by local governments at public halls and schools.

— The original Japanese article appeared in The Yomiuri Shimbun on June 2, 2021.