Last month, regarding the record heavy rainfall caused by river floods and sediment-related disasters mainly in western Japan, a study group of the Japan Meteorological Agency by experts said that the front stagnated due to the westerlies meandering to the south, and the total amount of rain observed was He pointed out that it is "abnormal weather", such as exceeding the heavy rains in western Japan three years ago.
From the middle to the end of last month, the front stagnated near Japan, and warm and moist air continued to flow from the south, resulting in record heavy rainfall in western Japan and Nagano prefecture.
Especially in northern Kyushu and the Chugoku region, developed rain clouds continue to be applied for a long period of time, and the amount of precipitation during the period from 11th to 26th last month is
1000 such as
1360 mm in Unzen City, Nagasaki Prefecture
and 1334.5 mm in Ureshino City, Saga Prefecture. The number of observation points exceeding the millimeter
has reached about half of the annual rainfall
in
normal years.
In addition,
▽ Hiroshima City also suffered a record heavy rainfall of 530 mm, which is more than four times as much as the average month of August, and river floods and sediment-related disasters occurred one after another in various places.
The Japan Meteorological Agency's "Abnormal Weather Analysis Study Group", which is made up of climate experts, held an extraordinary meeting on the 13th to analyze this factor.
According to this, two westerlies in the Northern Hemisphere meandered greatly in the eastern part of Russia and near the Korean Peninsula, respectively, and the Japanese archipelago was sandwiched between the Sea of Okhotsk and two high pressures in the south.
As a result, the front continued to stagnate from western Japan to eastern Japan, and a large amount of water vapor flowed into it from the south and southwest, activating the activity of the front, and the rain intermittently intensified over a wide area, resulting in heavy rain.
The total amount of rain observed at AMeDAS of the Japan Meteorological Agency was 270,640 mm in 16 days until the 26th, exceeding the "heavy rain in western Japan" three years ago, which caused enormous damage.
Also, in August, the Pacific High in the south extends to the north side of Japan, and there are many days when it becomes sunny and severely hot. I analyzed that it lasted for a period of time.
In addition, the study group called a series of heavy rains "abnormal weather", saying that analysis results showing the possibility that the amount of water vapor in the atmosphere increased due to the long-term rise in temperature due to global warming and the amount of precipitation increased. I can say that. "
Professor Naofumi Nakamura of the University of Tokyo, who serves as the chairman of the study group, said, "It was a situation that could be called" abnormal weather. " It can be considered abnormal in that the seasons are off. "
He also pointed out that similar abnormal weather could occur in the future, saying, "The amount of water vapor is steadily increasing due to the effects of global warming, and it is far more likely that unprecedented rainfall will be observed in various places. It's coming up. "
Total rainfall exceeding the "Western Japan heavy rain" three years ago
Last month's heavy rainfall, which continued to rain over a wide area centered on western Japan, exceeded the heavy rainfall in western Japan three years ago, with the total amount of rainfall at observation points nationwide by the Japan Meteorological Agency.
From the data, we can see the characteristics of "long rain", in which the risk of disaster has increased due to continuous rain for a long period of time, even if the number of short-term heavy rains and extremely heavy rains is not so high. ..
According to the observations of the Japan Meteorological Agency, it continued to rain intermittently over a wide area, mainly in western and eastern Japan, from the 11th to the 26th of last month when the front stagnated near Japan.
During the period, the rainfall was
1431 mm in Yanase, Umaji Village
,
Kochi Prefecture,
and 1426 mm in Ebino Plateau
,
Miyazaki Prefecture, which were
record rainfalls of 30% of the average annual rainfall.
In areas where special warnings were issued
,
▽ Mt.
Unzen in Nagasaki Prefecture was 1360 mm, 46% of the annual rainfall,
▽ Ureshino City
,
Saga Prefecture was 1334.5 mm, 57%, and
▽ Omuta City
,
Fukuoka Prefecture was 1072.5 mm. 56%,
▽ Hiroshima city was 530 mm, 34%, and in
some places it exceeded half of the annual rainfall in about two weeks.
The total amount of rain observed at 1029 AMeDAS sites of the Japan Meteorological Agency was 270,640 mm in 16 days until the 26th, and the heavy rain in western Japan caused enormous damage due to the rain that continued for 11 days in 2018. It means that it was a value exceeding 245,784 mm.
On the other hand, in this heavy rain, the number of rains that gathered in a short time was small, and it became clear that the risk of disasters increased due to the so-called "long rain" that continued for a long time.
During the period, the number of "extremely heavy rains" of 50 mm or more observed in one hour until every hour was 62 times nationwide, with an average of 3.9 times per day, far below the average of 6 heavy rains in western Japan.
No "extremely heavy rain" was observed during the period in Umaji Village, Kochi Prefecture, Omuta City, Fukuoka Prefecture, and Hiroshima City, which had record heavy rains.
Especially in Hiroshima City, the maximum hourly rainfall was 23 mm, which was observed on the 14th, but sediment-related disasters and inundation of houses occurred one after another.
"Evacuation order" is also prolonged "How long should you evacuate?"
"Which do not know what to do with the timing ..."
"When it rains in the so all regions, where the safety or I'll get lost if the refuge"
"It does not work as well anymore JR, roads to closed to traffic, I should stay at home"
this time Regarding the heavy rain in Japan, there were a series of posts on SNS saying, "I didn't know the timing of evacuation because of the long rain."
In the event of a disaster, information such as "evacuation instructions" and "evacuation for the elderly" issued by local governments will be helpful, but as the rain prolongs, the period during which information is released has become longer.
Even if the local government publishes the progress of the target area and date and time of the "evacuation order" on its website, some local governments continued to give instructions for about two weeks at the longest, and until the end of August.
Of these, Hiroshima City issued an evacuation order for 12 days at the longest, saying that there is a risk of sediment-related disasters and flooding of rivers.
As of 10 pm on the 14th, when the number of evacuees was the highest, a maximum of 2156 people had moved to the evacuation center.
In this heavy rain, a large amount of earth and sand flowed into houses and roads after the residents moved to evacuation centers, and there were many cases where damage was avoided.
A person in charge of Hiroshima City said, "It was unavoidable that the evacuation order was prolonged because there were some areas where the risk of sediment-related disasters continued even after the rain stopped. It was difficult to deal with it because there was a voice saying "Is it?"
Nagasaki Unzen Autonomous Chairman "I was surprised that it was raining so much"
Due to the record heavy rainfall last month, Mt. Unzen in Nagasaki Prefecture exceeded 40% of the total annual rainfall in the 10 days from the beginning of the rainfall on the 11th.
In Unzen City, a landslide occurred on the 13th of last month, killing three parents and children, and the hot spring town in the city also suffered damage such as no hot water.
Munetoshi Kato, the chairman of the local autonomy, recalled that although it had been raining for a long time, he did not expect such damage.
Mr. Kato said, "It has been raining for a long time, but I didn't feel that it was" insanely strong "compared to normal rain. I didn't think it would happen, so I didn't think about evacuation. However, when I woke up in the morning, a landslide had occurred, and at that time I was surprised to find out the total amount of rainfall, "Is it raining so much?" If I knew it, I would have evacuated. "
Expert "Change the awareness of evacuation"
Professor Katsuya Yamori of the Disaster Prevention Research Institute of Kyoto University, who is familiar with the evacuation behavior of residents in the event of a disaster, said, "The heavy rains hit mainly the areas that were severely damaged by the heavy rains in western Japan three years ago. Many people had clear memories of those days. One of the reasons why they were able to control the damage was that they were highly conscious of evacuation and were able to take immediate disaster prevention actions. "
On top of that, when it comes to the "long rain slapstick type" rainfall pattern, there is not much heavy rain that the residents feel is not just a matter of course, and it is very difficult to decide where to evacuate. It will be difficult to make decisions such as issuing or canceling. "
Furthermore, in order to protect himself from disasters, he said that it was not enough to follow the evacuation information of the government. When you notice something familiar to you, such as a color, it is even more important to share it with the people around you as an "evacuation switch" to evacuate immediately. " rice field.
He added, "The pattern of record-breaking heavy rains falling almost every year and becoming long rains is steadily increasing, and there is a risk that long-term evacuation will be required one after another, including the approaching typhoons. In the meantime, it is necessary to change the consciousness of evacuation from the conventional image of evacuation against storms and floods, which only surpasses the emergency, to the way of evacuation assuming that you will live in an acquaintance's house or hotel for a certain period of time. "