ICHARM > Message from Director

Message from Director


  Move on to a different dimension
    from 102 to 103

A hilly and mountainous area in northern Kyushu Island of Japan was seriously damaged in July 2017 by extremely heavy rainfall reaching up to 900mm/12hr, which was estimated using a radar-rain gauge network. Debris flows occurred throughout most of the area, covered with thick decomposed Granodiorite. A huge amount of sediment and fallen trees flowed down with a violent torrent and changed the tranquil landscape of the valley plain dramatically. The narrow river channels were completely filled with the sediment. Then, the flood flow with the driftwood spread while heaving up and down across the valley plain, claimed human lives, and destroyed houses, farmland and roads.

According to Chronicles of Japan, one of the country’s oldest histories, a royal palace was once constructed in the damaged area in the year 661. Since then, people there have been constructing infrastructure for livelihood and production, building communities, and developing and nurturing a culture for so long. The valley plain has been formed through geomorphological processes as occurred in 2017 without any doubt. A geographer says, “This is a textbook case of microtopography reformed by floods and sediment.”

In the recent flood management of major rivers in Japan, structures are planned for floods of 80-200 year return period. The IPCC 4th Assessment Report, published in 2007, asserted that the warming of the climate system due to anthropogenic green-gas emissions was unequivocal. Exactly the same expression was used in the 5th report in 2014. Associated with the climate change, heavy precipitation events are projected to increase in frequency, intensity, and/or amount. Actually, we are now experiencing heavy rainfall events of an unprecedented scale with the return period shifting from the 102 order to 103; events of that scale may cause far more drastic topographical modifications. The impacts of the changes can be even more serious in hilly and mountainous areas with smaller basin area and shorter flood travel time. All hydrologists are supposed to know these processes well. I am deeply ashamed of immature scientific knowledge and low-level actions against the changes. By developing our scientific imagination, we should urgently take up the challenge of building a resilient society to disasters of a different dimension.

31 January 2018
Toshio KOIKE
Director of ICHARM