News

by Michio Shimotaka, Staff Writer

On September 18, 1976, the national government defined the area where “black rain” containing radioactive materials had fallen after the U.S. atomic bombing, setting the “Health Examination Special Designated Area.” Accordingly, the revised Atomic Bomb Medical Relief Law provided residents of the area at the time with free health checkups and an Atomic Bomb Survivor’s Certificate if they developed certain diseases. However, the demarcated “boundary” continued to create a sense of unfairness among those outside the area.

In Hiroshima, the 19-kilometer-long, 11-kilometer-wide oval-shaped area stretching northwest from the hypocenter encompassed the entire Numata-cho district, and spread over the towns of Yasufuruichi, Asa, Itsukaichi, Yuki, and Kake, all of which are now part of Hiroshima’s Asaminami Ward, Asakita Ward, Saeki Ward, and Akiota town. The government categorized those effected as individuals who had been “in an environment where they were physically affected by radiation from the atomic bombing” and distinguished them from survivors who had directly experienced the bombing or entered the city right after that.

Based on the “heavy rain area”

In June of 1975, the government presented its position to the Committee on Social and Labor Affairs of the Upper House that there was no sufficient basis to provide support to people in the black rain area in Hiroshima, asserting, “Based on currently available materials, we do not believe people in the area were greatly affected by the bomb’s radiation.” They also responded they had received various strong requests from local communities.

The heavy rain area was determined based on the results of an interview survey conducted by Michitaka Uda and other technicians from the Hiroshima District Meteorological Observatory (now, Hiroshima Local Meteorological Office) shortly after the bombing. “The light rain area” outside the “heavy rain area” was excluded. The country kept refusing to expand the area, claiming no residual radioactivity from the atomic bombs was detected in the soil within 30 kilometers of the hypocenters of the Hiroshima and Nagasaki bombings, according to the investigations conducted in 1976 and 1978.

It is said there is a limitation on the survey because it was carried out amid the chaotic aftermath of the bombing. Isao Kita, who had joined in Mr. Uda’s survey, later recalled the so-called “Uda rain area” as tentatively decided.

Petition asking to expand the area

Chika Maeda, 83, Naka Ward, and Chizora Nishimura, 81, Asaminami Ward, are sisters who were exposed to the black rain on August 6, 1945, near their home in the village of Minochi (now part of Yuki-cho in Saeki Ward), located about 20 kilometers northwest of the hypocenter. “Our mother later told us she washed our clothes smeared with the rain.” However, they were just outside the black rain area. Their 87-year-old sister, who was on the other side of the Otagawa River, received an Atomic Bomb Survivor’s Certificate.

In 1978, the father of the sisters, Heizo Hanamoto (who died in 2007 at the age of 93), and others formed an association for the victims of the black rain being nursed at home. They began petitioning the central, prefectural and city governments, asking them to expand the area eligible for the relief law. However, the government did not change its position. Ryutaro Hashimoto, the Health and Welfare Minister at the time, replied in May of 1979 at the Committee on Social and Labor Affairs of the Upper House, that “it is not an issue that the administration can easily handle without scientific evidence or a foundation of some kind.”

“Does the rain fall beautifully in an oval shape?” Victims of the black rain posed this question to Yoshinobu Masuda, the now 101-year-old former head of the research laboratory at the Meteorological Agency’s Meteorological Research Institute and Tokyo resident, during the World Conference Against Atomic and Hydrogen Bombs held in Hiroshima in the summer of 1985. It was unthinkable the rain would have fallen uniformly from the cumulonimbus cloud that had been violently formed immediately after the bombing.

Mr. Masuda had read Record of the Hiroshima A-bomb War Disaster (published in 1971), memoirs written by A-bomb survivors, and collected accounts describing the rain. He also reinvestigated the testimonies collected by Mr. Uda’s team. With the cooperation of the association, he continued conducting on-site interviews with residents of present-day Yuki-cho and Kitahiroshima-cho, and examined 1,188 pages of questionnaires in an attempt to grasp the overall picture.

In 1988, Mr. Masuda announced the result that the black rain had fallen in an area approximately four times larger than the Uda rain area. Nevertheless, the government maintained its original position. Ms. Maeda and Ms. Nishimura joined the class action lawsuit, and won the case in 2021, obtaining the Atomic Bomb Survivor’s Certificate.

(Originally published on April 26, 2025)