‘Guerrilla rainstorm’ warning system aims to prevent soakings, or worse

Trevor Mogg

It’s no fun being caught in a so-called “guerrilla rainstorm,” and it can be downright dangerous if it involves hailstones or causes flash floods.

The term has been widely used in Japan since around 2008 when sudden and ferocious downpours caused a number of deaths across the country.

As the name suggests, such highly localized storms feel as if they appear from nowhere, though in fact they can be put down to moist ocean air hitting warmer air trapped among buildings, usually in a densely packed city.

Researchers in Tokyo are currently testing a technology that can forecast a guerrilla rainstorm and send out an alert around 30 minutes before it begins, giving urbanites ample time to plan ahead and get out of harm’s way. Or simply avoid a severe soaking.

The system, reported this week by Japan’s Mainichi newspaper, is a welcome improvement on current technology, which can only predict cloudbursts at the last minute.

Developed by a number of industry, government, and academic bodies that include Tokyo’s National Institute of Information and Communications Technology, the system works by combining advanced radar and radio wave data.

The weather radar is able to create a three-dimensional map of a rain cloud in 30 to 60 seconds, a notable improvement on current technology that takes around five minutes, and even then can only measure parts of the cloud. The new system not only measures the size and structure of the cloud, but also estimates the size of its raindrops.

The information from the radar is then combined with data collected by radio waves that estimate the amount of water vapor in the air, resulting in a more accurate prediction regarding the likelihood of a severe rainstorm occurring in a particular part of a city.

The team behind the technology is aiming to launch the system before the Tokyo Olympics, which takes place in 2020. Local weather services could use the data in its reports and send out smartphone alerts to the local population.

If all this talk of rain has put you in the mood to seek out a new umbrella, then do take a moment to check out our recently posted article highlighting some of our favorites, with each one built to withstand strong winds.

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