特別とくべつ警報けいほう相次あいつぐ 記録きろく的てき大雨おおあめ 背景はいけいは 被害ひがい特徴とくちょうは？専門せんもん家か【QA】

Due to the influence of a weather front, a special heavy rain warning has been issued in Kumamoto Prefecture, and record-breaking rainfall has occurred in northern Kyushu and Yamaguchi Prefecture, resulting in a series of damages.

Why did we have heavy rain in August like the end of the rainy season? What are the characteristics we can see from the current damage? We asked an expert.

Expert on the mechanisms of heavy rain We interviewed Professor Kazuhisa Tsuboki of Nagoya University and Yokohama National University, who is knowledgeable about the mechanisms of heavy rain.

Record-breaking rainfall brought by an atmospheric river with the largest amount on Earth

Why did we experience such record-breaking heavy rain? It is believed that the cause was the formation of a so-called atmospheric river, where water vapor flowed in like a river and continued to pour into a stationary front for an extended period, resulting in a large amount of water vapor accumulating.

It is an overwhelming amount of water vapor—so much that it could be said to be the maximum amount the Earths atmosphere can possibly contain.

In addition to the water vapor coming in from the western continent, southwesterly winds over the East China Sea also flowed along the front.

Since the front had stalled, a flow of water vapor continued to move into the same area for a long time, resulting in heavy rain.

It’s been over a month since the rainy season ended, but I think it’s really rare for something like this to happen in August.

Q

Why does the front continue to stagnate? The position of a stationary front is determined by the tug-of-war between the high-pressure system to the south and the high-pressure system to the north.

At present, it seems that these forces are evenly matched and the situation remains at a stalemate.

If the Pacific high-pressure system strengthens, the front will move north, but thats not the case right now.

Linear rainband = Disaster Q

Heavy rain is expected to continue on the 12th and 13th.

What should we be careful about? Since the inflow of water vapor—the atmospheric river—is still ongoing, it definitely does not mean that things are now safe. As long as the atmospheric river continues, there is still a significant possibility that a linear rainband could form somewhere.

A linear rainband brings extremely heavy rainfall, so you should think of a linear rainband as equivalent to a disaster. If a linear rainband is forecast, it’s important to recognize that the situation is extremely dangerous.

I want you to stay alert for this heavy rain for a while, especially for linear rainbands.

However, the problem is that it is difficult to clearly predict where a linear rainband will occur.

I would like people to pay attention to weather information and, if they are in areas where there is a possibility, to evacuate appropriately in advance.

Especially, I think it is quite possible that there will be heavy rain from late at night until early morning.

I think the most important thing is to evacuate properly before it gets dark.

Q

Professor Tsuboki has been conducting observations of water vapor and other factors in atmospheric rivers using aircraft. What have you learned so far? We are gradually beginning to understand the diversity of atmospheric conditions that cause linear precipitation zones.

Sometimes moist air flows only into the lower layers of the atmosphere, while other times, moist air flows all the way up into the upper layers.

In the recent heavy rainfall in Kyushu, water vapor mainly came in from the west, but if we could also observe such phenomena, it is believed that the accuracy of forecasts would improve.

Expert Investigating Heavy Rain Damage Across the Country We interviewed Professor Motoyuki Ushiyama of Shizuoka University, who has been investigating the situation of heavy rain damage in various regions.

Damage occurs where there is a disaster risk Q

Are there any characteristics of this heavy rain that can be seen from the damage so far? It was a record-breaking rainfall, and for each region, it was the kind of rain that hasnt occurred in at least several decades.

On the other hand, the damage has occurred in areas that are geographically considered dangerous.

For example, the landslide disaster that occurred in Kosa Town, Kumamoto Prefecture, appears to have happened within a landslide disaster warning area, which is designated as a high-risk zone for landslides according to the hazard map.

Based on my investigation of past disasters so far, I found that about 90% of landslides that result in human casualties occur within designated landslide warning areas, and it appears that this case also falls into that category.

Also, there was a case where a person was swept away in a river in Fukutsu City, Fukuoka Prefecture, but the area along the river was a place where flooding was expected according to the hazard map.

Even in areas where flooding is not anticipated on the hazard map, there were places where flooding appeared to have occurred in so-called lowlands, which are areas lower than the river embankments, when looking at the terrain.

At this point, my impression is that there hasnt been a disaster that would make us think, Theres no way something like that could happen here.

If it doesnt become a special warning, its okay is incorrect Q

There have been reports of damage even in areas where no emergency warning was issued, but how should we assess the risk of a disaster occurring? Just because an emergency warning hasnt been issued doesnt mean its safe at all.

For example, if a special warning has been issued in a nearby city or town, there isnt such an extreme difference in the level of danger.

On the Japan Meteorological Agencys website, the Kikikuru system allows you to check the risk levels of landslides, flooding, and other hazards by region. The most severe warning is indicated by black, but in the past two years, it has become more common for significant damage with casualties to occur in areas marked one level lower, with purple, rather than black.

So, I hope you wont focus only on information like special warnings or linear rainbands, but instead use various sources to assess the level of danger, such as Kikikuru and the Ministry of Land, Infrastructure, Transport and Tourisms River Disaster Prevention Information website, where you can also check water levels and river monitoring cameras.

Check information about your area where heavy rain continues.

It is expected that rain will continue to fall in various areas.

What should we be careful about? When there is record-breaking heavy rain that leads to a special warning being issued, people tend to focus only on the areas where the rain is falling.

Of course, continued caution is needed in Kyushu, but in some areas such as the Chugoku region and parts of Hokuriku, the risk of landslides is increasing, and there are regions where landslide warnings have been issued.

I think we need to be careful about rain over a fairly wide area from western to eastern Japan on the 12th as well.

Its not that only Kyushu will be greatly affected; I want everyone to thoroughly check the latest weather and disaster information for their own area and where they live.

Advance awareness of risks and avoiding dangerous places Q

During the Obon holiday, I think many people are going back to their hometowns or going out to have fun.

What should we be careful about? In order to understand the risks of the places you plan to visit in advance, it is important to check resources such as the Ministry of Land, Infrastructure, Transport and Tourisms Hazard Map.

However, there are also disaster risks such as small rivers that are not shown on hazard maps, so its important not to rely too much on them.

During heavy rain, do not go near cliffs where there is a risk of landslides, along mountain streams, or near rivers.

I think its important to keep things like this in mind.