High tolerance land use against flood disasters: How paddy fields as previously natural wetland inhibit the occurrence of floods

Although natural disturbances are inherent in any ecosystem, they can be hazardous to the local residents, indicating that it is necessary to mitigate these disturbances as much as possible appropriately. There has been an increased interest in taking advantage of ecosystem functions for disaster risk reduction (Eco-DRR) as future infrastructure because of the lower introduction, maintenance costs, and the additional ecosystem services. Previous studies have suggested that intact ecosystems have a higher tolerance and/or resilience to natural disturbances. However, fully intact ecosystems have been decreasing rapidly worldwide. This study evaluates the functions of semi-natural land, namely, paddy fields, which is one of the typical agricultural land uses of monsoon Asia to reduce the societal damages of natural disasters. As semi-natural land is sometimes located close to or is similar to the original intact habitat, it could play a role in reducing flood disasters. In particular, paddy fields could be seen to be similar to intact wetland habitats, most of which have disappeared in recent decades due to development. To test this idea, the relationships between flood disasters and paddy fields with location condition in inland regions of central Japan were evaluated. We used flow accumulation value (FAV) as an index of intact wetland habitat; particularly, we considered that high FAV area might be previously natural wetland. Thus, paddy field located at high FAV values are considered similar to intact wetland habitats. Results showed that paddy fields located in high FAV areas were able to significantly reduce flood frequencies, occurrences of landslides, and debris floods. These results suggested that semi-natural land close to or on their natural habitats could function as intact ecosystems and provide Eco-DRR function as ecosystem services. These types of semi-natural land could be employed as green infrastructure to provide several extensive ecosystem services.