Agricultural land near where rivers meet can mitigate floods

Tokyo, Japan – Researchers from Tokyo Metropolitan University showed that agricultural land preserved around river confluences can help mitigate floods. They make a case for Eco-DRR, an approach that uses existing environmental resources to improve resilience against flooding. Statistical analysis showed that municipalities with agricultural land in areas with high water storage potential suffered fewer floods, with stronger correlation when agricultural land was situated near river confluences. The team hope their findings inform effective land usage.

Climate change has brought about an increased risk of extreme weather, which is particularly concerning for areas at risk of floods. As society seeks to navigate this unprecedented challenge, local authorities are scrambling to come up with the most effective measures to prevent and mitigate severe flooding. One answer might be dams and barriers, but there is a limit to what can be achieved, particularly when balanced with their own ecological impact.

An alternative approach is Eco-DRR (Disaster Risk Reduction), an approach that seeks to use existing environmental resources, especially agricultural land, to reduce risk. Agriculture is important for society for food production, but it has an important secondary role in reducing flood damage by soaking up and temporarily stopping large amounts of water. But its efficacy depends widely on the placement of farmland, and how it is maintained.

Associate Professor Takeshi Osawa from Tokyo Metropolitan University is at the forefront of efforts to study the impact of Eco-DRR on disaster mitigation in Japan. Japan is a particularly mountainous country, where maintaining large tracts of farmland is difficult, with migration of people from rural areas to the cities leading to the abandonment or urbanization of formerly agricultural land. Thus, it is becoming increasingly important to understand the specific role that agricultural usage plays in flood risk.

In his most recent work, he undertook a wide-ranging statistical analysis of the placement of agricultural land in different municipalities compared to local risks of flooding. He analyzed surveys of flood damage in 1917 municipalities all over Japan spanning the period from 2010 to 2018, and looked at how much agricultural land was situated on areas with high water storage capacity. He found that municipalities with land that fit these conditions had a lower risk of floods. Combining detailed geographical data, there was an even stronger connection between the area of farmland located at the confluence of rivers and a reduced risk of flooding, stronger than the correlation found from agricultural land on areas with high water storage potential.

Confluence points between rivers exist all over Japan and are safe havens for a wide range of flora and fauna that can benefit from the flooding. Bringing together food security, disaster mitigation, and biodiversity, this presents a rare win-win scenario in the face of an increasingly challenging climate environment.

This work was supported by the Environment Research and Technology Development Fund (JPMEERF20222G01) of the Environmental Restoration and Conservation Agency of Japan and the Water Resources Environment Center of Japan.