Tokyo working on alert system for ‘guerilla rainstorms’

guerilla rainstorms alert system, the venture magazine

Situated at the eastern end of Asia, with a good chunk of the city below sea level, Tokyo is particularly vulnerable to wet weather. “Guerilla rainstorms” often rise up without warning, dumping water on low-lying areas and causing widespread flooding. With the city set to play host to the Rugby World Cup this September and October, and the Olympics next year, officials are developing a warning system capable of predicting rainstorms and tornadoes 20 to 30 minutes before they arrive.

Mainichi reported that the system uses a new type of weather radar and digital radio waves that estimate how much water vapor is in the air. The “multi parameter phased array weather radar” (MP-PAWR) uses a flat antenna to send radio waves out over a wide range. The MP radar measures the size of raindrops, while the PA radar quickly makes 3D scans of cloud structures.

Rainstorms dumping more than 80 millimetres in an hour occur almost 20 times per year on average in Tokyo, and that number is rising along with ocean temperatures. Summertime, when the Olympics will be held, sees an increase in sudden downpours. The Japan Society of Civil Engineers has said that a large flood in the eastern part of the city could kill hundreds of people and cause billions of dollars in damage.

guerilla rainstorms alert system, the venture magazine

City in the Rain: Torrential downpour at rush hour in Tokyo street at night with people scurrying for shelter across wet pavement reflecting neon lights.


“We hope to put the technology, directly linked to the lives of people, into practical use as soon as possible,” a National Institute of Information and Communications Technology official told Mainichi.

A study conducted last year by Newcastle University and the University of Adelaide found that rainstorm intensity is increasing in Australia, as well, bringing two to three times more rainfall than expected.

“This large increase has implications for the frequency and severity of flash floods, particularly if the rate stays the same into the future,” University of Adelaide associate professor Seth Westra said. “We have always been a country of weather extremes, and it seems that climate change is causing both the dry and wet extremes to intensify.”

Perhaps if Japan can perfect its MP-PAWR system, the technology will spread throughout the Asia-Pacific region, giving advanced warning to coastal areas susceptible to dangerous flooding.