JBA rolls out Japan flood update

Risk modelling specialist JBA Risk Management has updated its Japan Flood Map.

JBA said the latest model is underpinned by new terrain data, improved methods, and new national defence data.

Due to Japan’s climate and geographical location, it faces flood risk from numerous sources. Tropical cyclones and typhoons pose a significant risk each year to communities throughout Japan, particularly during spring and summer and can bring heavy rainfall alongside strong winds (Japan Meteorological Agency). 

In 2019, Typhoon Hagibis was the nineteenth typhoon of the season and the worst storm to hit the country in 60 years. It brought unprecedented rainfall and flooding to eight prefectures across Japan’s main island, Honshu, as well as landslides.

Alongside risk from typhoons and cyclones, and often compounded by these events, Japan is host to several major river systems which can bring widespread flooding following heavy rainfall and storms. 

During Typhoon Hagibis, at least 142 rivers flooded in Honshu, including the major Arakawa, Chikuma and Tama rivers. During the July 2020 floods in Kyushu, which caused at least 72 fatalities, several rivers overtopped their banks to flood surrounding areas, including the Kuma River and Chikugo River.

Updates to the latest JBA Japan flood model include new bare-earth terrain data covering 100% of the country; new land cover dataset; improved surface water and river flood type classifications; and new national flood defence information, including over 1,000 new flood defences.

The update also incorporates validation against major events, including Summer 2020 flooding and Typhoon Hagibis.