Abstract
Due to heavy rainfall caused by the Baiu- front, 24 hours of precipitation resulted in a
record-breaking 400 mm of rainfall from noon of July 3, 2020, to noon on July 4, mainly
within the Amakusa, Ashikita and Kuma Districts. This heavy rainfall made it impossible
to record the water level after the 7:30 am water level of 12.88 meters on July 4 since it
flooded the Watari Observatory in Kuma Village located at the mid-stream of the Kuma River.
An intensive care home for the elderly in the Watari area, “Senjuen” is located in the lowlying
area of floodplain, and according to the planned scale flood-hazard map, it is not in the
inundation assumption area. However, when it comes to the largest-assumption scale floodhazard
map, it could flood 10 to 20 meters. Thus, 14 residents died because the rapidly rising
water level resulted in there not being enough time to evacuate the upper level of the building.
The maximum height of inundation trace was recorded at 760 cm on the Mine community in
the Watari area, and this aligns with the estimated inundation map of 8 to 9 meters that the
Geographical Information Authority had predicted.
