Heavy rain special warning "cancel" to "switch" To call for warning of flooding 16:17 on June 16

Last year's Typhoon No. 19 was a flood of rivers after the special warning for heavy rain was lifted. In response to this, the Ministry of Land, Infrastructure, Transport and Tourism and the Japan Meteorological Agency have expressed the "release" of the special warning as "switching" and also indicate the possibility that the water level will rise up to 24 hours ahead in large rivers such as the Tone River and the Abukuma River. Information was announced, and even after the peak of heavy rain had passed, people would be wary of flooding.

In Typhoon No. 19 last October, there were a number of cases where rivers flooded after the Meteorological Agency canceled the special warning for heavy rain. There were many people returning home from.

The special warning that calls for maximum caution is not intended for river flooding, and the issue was how to convey the danger of flooding that occurs at a time lag after the special warning was canceled.

In response to this, the Ministry of Land, Infrastructure, Transport and Tourism and the Japan Meteorological Agency amended the term “release” of the special warning to “switch” to the warning, and if the water level is rising in approximately 300 rivers managed by the state, We will announce new information "River Flood Information" that shows the forecast.

When switching the special warning, in addition to showing a forecast of the water level increase up to 6 hours ahead, it means that the 14 large rivers such as the Tone River and Abukuma River will show the water level up to 24 hours ahead.

When presenting information, the Ministry of Land, Infrastructure, Transport and Tourism and the Meteorological Agency jointly hold a press conference to explain which rivers are at risk of flooding, and to be alert to river flooding even after the peak of heavy rainfall. , I call it strongly.

Target is a nationally managed river

"Information about river flooding" is information newly announced by the Ministry of Land, Infrastructure, Transport and Tourism and the Meteorological Agency to convey the risk of flooding even if the heavy rain special warning is switched to the heavy rain warning. The target is the "Flood Forecasting River" managed by the national government, which has 298 water systems and 298 rivers nationwide.

In the information, we will announce the current water level situation and forecast of the water level up to 6 hours ahead at the reference observation point.

Furthermore, for 11 rivers and 14 rivers with a particularly large catchment area, such as the Tone and Ara rivers that flow in the Kanto region, the Abukuma river that flows in the Tohoku region, and the Agano river that pours in Niigata prefecture, in addition to forecasting the water level up to 6 hours ahead, We will announce the expected rise in water level from half a day to 24 hours ahead based on cases etc.

However, "information on river inundation" is announced for large rivers managed by the national government, and not for small and medium rivers managed by prefectures.

For small and medium-sized rivers, it is necessary to check the "flood risk information" and "water level information" announced by the prefectures, and the "flood risk distribution" that can be found on the website of the Meteorological Agency, etc.

Time lag between heavy rain peaks and river floods

Last year's Typhoon No. 19 released information to inform the occurrence of floods in eight rivers after the heavy rain special warning was lifted, and it is once again highlighted that there is a time difference between the peak of heavy rain and the inundation of large rivers. It was

The eight rivers are the Yoshida River in Miyagi Prefecture, the Abukuma River upstream in Fukushima Prefecture, the Ishida River in Gunma Prefecture, the Jirao River in Tochigi Prefecture, the Kuji River in Ibaraki Prefecture, the Tokugawa River in Saitama Prefecture, the Koshibe River in Saitama Prefecture, and the Chikuma in Nagano Prefecture. It's a river.

The difference in the time to release the special warning and the information that the flood occurred was 9 hours and 20 minutes in the upper Abukuma River, followed by 8 hours and 20 minutes in the Tokugawa and Koshibe rivers, and about 4 hours in the Yoshida river Later, the Chikuma River is about two and a half hours later.

On the other hand, in a questionnaire conducted by the Japan Meteorological Agency for 300 people who took evacuation behavior at that time, about 30% of people said, "Because we learned that the heavy rain special warning was lifted, we thought that it was a safe situation It has been pointed out that the cancellation of the special warning was mistaken for relief information.

Water level rise time difference Case of Tone River

The rise in water level after the peak of heavy rain, which was a problem for Typhoon No. 19 last October. Let's take a look at the situation at the time on the Tone River, which flows through a wide area of ​​the Kanto region.

In Gunma and Tochigi prefectures, which are the upper reaches of the Tone River, the rainfall from the beginning of the rainfall was over 400 mm at each observation point.

In Ibaraki Prefecture, which is located downstream, the heavy rain special warning was canceled at 2:20 am on October 13.

At this time, at the observatory upstream of the Tone River, the water level of the river, which is the basis for the announcement of flood forecasts, had reached the "flooding risky water level", which would not be a problem at any time.

On the other hand, at the Yokotone observatory in Inashiki City, Ibaraki Prefecture, where the special warning was canceled, the water level of the river was the "water tank standby water level", which was lower than the "flood caution water level" that calls attention to flooding.

However, since a large amount of rainwater flowed from the upstream, the downstream water level increased steadily, and the water level exceeded 4 meters at about 6:00 pm on the 13th, 15 hours after the cancellation of the special warning, and became a flood risk water level. I have reached

To add surveillance cameras

In addition to transmitting new information, the Ministry of Land, Infrastructure, Transport and Tourism will strengthen the surveillance system by increasing the number of surveillance cameras installed along the river.

According to the Ministry of Land, Infrastructure, Transport and Tourism, in October last year, Typhoon No. 19 caused flooding in 19 rivers managed by the country, mainly in the Kanto and Tohoku regions, but the flood information cannot be announced because the site cannot be confirmed. There was also.

Among them, there were cases where it was not possible to confirm the inundation or collapse due to the inundation spreading and the staff not being able to approach the site, or because the site was a blind spot for surveillance cameras.

In response, the Ministry of Land, Infrastructure, Transport and Tourism has decided to strengthen the surveillance system by increasing the number of river surveillance cameras and water level gauges throughout the country.

By the end of March next year, we would like to increase the number of surveillance cameras from the current 8,000 to approximately 1,900, and hope to quickly announce information on river floods and landslides.