Abstract
This report summarizes a field survey of heavy rainfall disasters in Kyushu from August
6-11, 2025. Surveyed areas were Yatsushiro, Tamana, Kami-Amakusa, and Amakusa in
Kumamoto Prefecture. Western Yatsushiro recorded a cumulative rainfall of 646 mm, with over
500 mm observed widely. Based on local investigations, this report describes the inundation
heights estimated from flood marks and flow behavior. Clear flood marks were identified at
many sites; areas such as the Naka (Tamana) and Aitsu (Kami-Amakusa) districts showed
inundation depths exceeding 90 cm. In Amakusa, overflow damage occurred due to driftwood
obstructing the piers of the Gion Bridge. Comparisons with the hazard maps confirmed general
consistency, despite localized discrepancies. Amid concerns of increasing record-breaking
rainfall due to climate change, this study confirms that hazard maps remain highly useful for
disaster risk and evacuation planning
