Production of flood hazard maps along rivers in Kyushu is lagging far behind other regions in Japan, with less than a quarter of municipalities required by law to create such maps having finished the work as of the end of March.
In the aftermath of the powerful Typhoon Hagibis, which hit Japan on Oct. 12, the Land, Infrastructure, Transport and Tourism Ministry is calling on municipalities nationwide to include areas along smaller rivers on the maps. But slow progress in flood hazard mapping, which stems from the extra work needed to update inundation predictions, is likely to cause further delays in municipal flood preparedness.
As Kyushu is expected to receive more heavy rain than other regions due to climate change, local governments have been urged to take measures against disaster risks as quickly as possible.
Under a 2015 amendment to the Flood Prevention Act, the central government requires all 1,347 municipalities that have areas prone to flooding to make hazard maps showing evacuation routes and evacuation centers.
But according to the land ministry, only 23.1 percent, or 41 of 177 municipalities subject to the requirement in Kyushu, have finished making the maps. The figure compares with 33.1 percent nationwide.
Even in Saga Prefecture, which is the most advanced prefecture in Kyushu in terms of disaster preparedness, the figure stood at 44.4 percent. Figures for municipalities in Oita Prefecture were at just 6.2 percent, and those in Kumamoto Prefecture were at 9.5 percent.
A lack of progress in the preparation of prefectural-level flood forecasts has been raised as one of the reasons for the slow production of hazard maps by municipalities. These forecasts, containing information on expected flood depth and areas of floods along each river when they overflow, are used as resources to make hazard maps by municipalities.
By the end of March, these forecasts had been prepared along all 448 rivers administered by the central government, but such work has been done for only 54.2 percent, or 883 rivers, out of the 1,627 rivers administered by prefectures.
Kyushu, Fukuoka, Saga, Oita, Miyazaki and Kagoshima prefectures had compiled flood forecasts by the end of October, but the information is not fully reflected in hazard maps made by municipalities. Nagasaki Prefecture is still gathering information and plans to compile it by March, while Kumamoto will likely continue work through the next year.
Recent powerful storms, like Typhoon Hagibis, have caused damage not only to areas along major rivers, but also damaged river banks in areas that weren’t included in existing hazard maps.
The aftermath of these powerful storms has prompted the land ministry to expand the areas covered by flooding forecasts along smaller rivers. This means the municipalities that have already prepared inundation hazard maps may be required to revise them.
Kenichi Tsukahara, a Kyushu University professor specializing in disaster risk reduction, said that if inundation estimates for smaller rivers are reflected, updated maps will show that wider areas are prone to flooding.
“In such a case, some evacuation centers designated by local governments may become unusable,” Tsukahara said. “It will also take a lot of time to create new evacuation plans.”
With flooding expected to become more frequent over time due to climate change, the land ministry will pursue drastic changes in its flood-control policies.
Experts forecast that if temperatures rise by 2 degrees Celsius by the end of this century, rainfall in the northwestern parts of Kyushu will increase by 15 percent, exceeding an anticipated average of a 10 percent rise nationwide.
“Some municipalities will need to take new preventive measures, such as by using private facilities as evacuation centers,” Tsukahara said. “To deal with the matter quickly, more state support for municipalities is essential, and understanding from local communities is also needed.”
This section features topics and issues from the Kyushu region covered by the Nishinippon Shimbun, the largest daily newspaper in Kyushu. The original article was published on Nov. 10.