Japan develops new radar to rapidly detect torrential rains

The Japanese government has developed a weather notification system that will allow local governments to detect signs of isolated torrential rain using a small radar and alert residents within five minutes to the forecast amount of rainfall and areas in danger of flooding.

The government will compile guidelines on using the system by next summer and encourage local governments to introduce it by subsidizing up to half of the necessary costs. The Land, Infrastructure, Transport and Tourism Ministry will include necessary costs in its budget request for fiscal 2017.

Unlike heavy rain caused by typhoons, localized torrential rain is triggered by the rapid expansion of cumulonimbus clouds. Quick bursts of heavy rain centered on small areas have unleashed landslides and flooded roads in various locations across the nation.

The Japan Meteorological Agency and the land ministry have set up large radars atop mountains and other locations that are capable of covering wide areas. However, localized downpours can materialize very soon after cumulonimbus clouds develop, making it difficult for radar to obtain enough data to make accurate forecasts.

The latest system adopts a smaller radar measuring about 1 meter in diameter and weighing about 65 kilograms that is better suited to tracking localized rainfall. It can detect rainfall within a radius of several tens of kilometers - large enough to cover most administrative areas. The radar is portable and can be installed on the rooftops of buildings. Each device is expected to cost several tens of millions of yen.

The radar works with software that forecasts rainfall amounts and areas where flooding is set to occur within the hour, allowing local governments to issue evacuation alerts five minutes after the system first detects cumulonimbus clouds or take necessary measures for sewage facilities.

The government has been working with Kobe University and private companies to develop the radar and software, conducting quality assurance tests in Fukui and Toyama prefectures since fiscal 2015. The government has confirmed the effectiveness of the system and decided to begin nationwide implementation starting next fiscal year.

In 2014, a sediment disaster in Hiroshima left 77 people dead. The incident prompted domestic research facilities and universities to conduct various research projects aimed at developing forecasting technology.

A research team led by the Kobe-based RIKEN Advanced Institute for Computational Science has been employing cutting-edge radar technology, climate satellites and supercomputers to reduce the amount of time needed to forecast downpours to 30 minutes before they start. Practical use of the system is expected to help reduce disasters but could take some time to implement.

Local governments rather than the meteorological agency or other government organizations will be able to operate the small-radar system, enabling municipalities to quickly respond to torrential downpours.

"The system can have an immediate impact, so we encourage municipalities to introduce it," a senior land ministry official said.