A man looking at stock prices during rain in Tokyo, 2002.
Photo: Koichi Kamoshida (Getty Images)

Officials in Tokyo are testing a new technology that utilizes weather radar and terrestrial digital radio waves to “quickly and precisely predict torrential rain and tornadoes” up to 20 to 30 minutes in advance, the Mainichi reported on Sunday.

The new technology is being developed by “industry, government and academic bodies including the National Institute of Information and Communications Technology (NICT)” based in Koganei, the Mainichi wrote, and is hoped to be ready for deployment ahead of the 2020 Tokyo Olympics and Paralympics. Existing radar systems are limited in their ability to predict “guerilla rainstorms,” so called because they form quickly from rising, cooling water vapor and strike with little warning in specific areas. However, the new system is much more powerful and capable of estimating the size of raindrops and the structure of clouds, the Mainichi wrote:

Developers say the new “multi parameter phased array weather radar” (MP-PAWR) being tested can predict torrential downpours and tornadoes 20 to 30 minutes before they occur. This is because it has a flat antenna that emits radio waves over a wider range than the rotating bowl-shaped antennas used in traditional radars. It is a combination of an MP radar that enables observation of the size of raindrops, and a phased array radar that provides 3-D scans of the structure of clouds in about 30 seconds.


The phased array is then paired with terrestrial radio waves which can be used to measure incredibly minute variations in water vapor levels, which can help narrow down the timing of a potential storm by showing weather personnel when the vapor is likely to rise high enough to cool and condense, Mainichi added.

As the Guardian wrote in 2015, predicting sudden, torrential rainfall is a major priority for Japanese officials, as around 30 percent of Tokyo lays below sea level and preparations for catastrophic flooding are widely known to be inadequate. In 2018, Reuters reported that the Japan Society of Civil Engineers had estimated a massive flood in eastern Tokyo “would kill more than 2,000 people and cause 62 trillion yen (422.7 billion pounds) in damage,” while officials acknowledged that the pace of construction was still very slow.

Scientists believe that the noted surge in the number of guerilla storms in Japan in recent years is linked to climate change, Reuters noted:

Intense rainfall is on the upswing across Japan. Downpours of more than 80 millimetres in an hour happened 18 times a year on average over the 10 years through 2017, up from 11 times between 1976-85.

... “Higher ocean temperatures cause more moisture to get sucked up into the air,” said University of Tokyo’s [disaster engineering professor Toshitaka Katada]. “That means a very large amount of rain falling at once, and typhoons are more likely to grow stronger.”


According to the Mainichi, preliminary tests of the system have been ongoing since 2018, with one NICT official saying they intend to bring it “into practical use as soon as possible.”

[The Mainichi]