Weather experts warn of a dangerously wet early July period


Meteorologists are urging the public to be on their guard at the start of July, which has become an annual season of heavy rains, landslides and floods.

Since 2017, at least one deadly disaster caused by torrential rains has occurred every year during the period from July 1 to 10.

A total of 430 people were killed or missing in these disasters, according to data from the Fire and Disaster Management Agency.

Weather experts say there is no reason to expect this year to be drier.

“Heavy rains occur every year, but in recent years especially, downpours that cause disasters have frequently occurred in early July,” Masaki Sato, a professor of meteorology at the University of Tokyo, said at the symposium. Japan Meteorological Society held in May.

On July 3, 2021, torrential rain triggered a deadly landslide in Atami, Shizuoka Prefecture.

A week later, a special heavy rain warning was issued in Kagoshima Prefecture in Kyushu and other areas. More than 200 buildings were flooded.

In July 2018, torrential rains hit western Japan, flooding rivers and causing mudslides.

The special heavy rain warning is issued for supposedly rare rainfall that occurs once every several decades.

Since 2013, when the alert was established, it has been issued 20 times, including nine times in early July.

With the exception of 2019, the warning has been issued in early July every year for the past five years.

The period is called the end of the “tsuyu” season, when conditions are favorable for heavy rains.

Rainy areas generally stay in southern China around June and move north around July, making the atmosphere over Japan unstable.

Additionally, the large amount of water vapor entering Japan can cause rows of thunderclouds to form.

Under these conditions, long linear bands of rain that continue to dump rain over large areas may occur in the same areas.

Linear rain bands have formed in early July for each of the past five years. They grow rapidly and their locations and times can change with small changes in conditions.

Linear rain bands are harder to predict than typhoons, and residents can be caught off guard by downpours from the rain bands.

That’s why experts advise the public to check weather information frequently.

On the evening of July 3, 2020, the Japan Meteorological Agency predicted up to 200 millimeters of rain over 24 hours in Kumamoto Prefecture. But in several places in the prefecture, more than 400 mm were recorded over this period.

The special heavy rain warning was issued before dawn on July 4.

The rain had already flooded the Kumagawa River and more than 60 people who could not flee died.

The JMA chief said at a press conference held later, “We were unable” to predict such a disaster.

In June of this year, the agency began simulating occurrences of linear rainbands six hours to half a day before their expected formation.

The JMA also provides a broad calendar for such events and shares information with the public.

Some local governments have decided to disseminate evacuation information more quickly through these simulations.

On the agency’s website, individuals can see rain forecasts several hours later based on radar observations. They can also consult a map detailing the risks of mudslides and floods in their area.

Shingo Shimizu, senior researcher at the National Research Institute for Earth Science and Disaster Resilience, urged people to keep up to date with the latest information.

“At this time of the season, the weather forecast can change at a fraction of the time,” he said.

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