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In recent years, record-breaking torrential rain has been increasing during the rainy season. The Japan Meteorological Agency and local governments are urged to make efforts to disseminate appropriate information so that people living in hazardous areas can begin evacuating as soon as possible.
The linear precipitation band is a phenomenon that has been attracting attention as a cause of disasters such as floods and landslides. Moist air from the ocean generates a succession of cumulonimbus clouds that dump strong rainfall over a short period of time, in a band of 50 to 300 kilometers.
In July 2020, torrential rain that hit Kyushu caused the Kuma River running through Kumamoto Prefecture to overflow, leading to the deaths of 88 people. Torrential rain in western Japan in 2018 also left widespread damage in various areas. It has been pointed out that heavy rainfall has been linked to global warming, so vigilance must be maintained from now on as well.
Last year, the JMA introduced a system to issue information on significant heavy rainfall to call for caution when the formation of a linear precipitation band is confirmed. However, when this information was issued, heavy rain had already begun to fall, so local governments and residents were limited in what they could do to deal with the situation.
In response to such a circumstance, a new system will be introduced in June to forecast half a day in advance the formation of a linear precipitation band.
It is commendable for the JMA to be willing to go one step further to make the forecast, having a sense of urgency about linear precipitation bands, which cause major damage almost every year.
Many residents may feel hesitant to evacuate in the middle of heavy rain late at night. If forecasts are issued during the daytime, local governments will be able to evacuate at an earlier time those residents who will be in imminent danger.
In the first place, localized phenomena such as linear precipitation bands are difficult to predict. Even throughout the world, little research has been conducted on them, and the detailed mechanism of their formation has not been fully elucidated.
To realize the forecasting system quickly, the agency said it has strengthened observations of water vapor at sea with the cooperation of private vessels, and it has also made use of supercomputers among other equipment.
The accuracy of the new forecasting system is not yet sufficient, so forecasts may end up incorrect for the time being. It is important for residents to take actions to protect themselves by combining forecasts with information such as that provided by local governments.
The JMA said it is planning to narrow the scope of its forecasts from wide areas to prefectural and municipal units. The agency is urged to work to provide more accurate forecasts.
Natural disasters often occur over a wide area. Therefore, cooperation between relevant government bodies including the JMA and local governments is essential. Disaster prevention information, including forecasts of linear precipitation bands, must be shared and disseminated to residents in an easy-to-understand manner that will lead to prompt evacuations.
