The study evaluated how well a GCM can reproduce the past weather patterns linked to the heavy rainfall events in Davao river basin by using raingauge and ERA5 data as reference. Our findings show that MRI-AGCM 3.2S reproduced similar weather patterns in JJA and DJF seasons as compared to ERA5 but due to small differences in configuration lead to biases in the local rainfall. This method can be also applied to other river basins and for evaluating how the future local rainfall will change.

This paper presents a trial estimation result of quantitative flood damage reduction effect by installing a spillway on a riverine levee in a protected area for promoting the “River Basin Disaster Resilience and Sustainability by All” (Ryuuiki-chisui) initiative which is strongly promoted in Japan. The result shows that flood damage is considerably reduced, e.g. average annual damage to paddy fields in the area can be expected to decrease, although the inundation frequency will increase.

Tritium-estimated groundwater mean transit times (MTTs) and storage volumes provide useful information for water resources management especially during droughts. In Hokkaido, we find that (1) one tritium measurement at baseflow is already sufficient to estimate MTT for some catchments, (2) the hydrogeological settings control tritium transit times of subsurface groundwater storage at baseflow, and (3) in future, one tritium measurement will be sufficient to estimate MTT in most Japanese catchments.