Global and social factors impacting agricultural pond discontinuation in Japan

Japan typically experiences a substantial annual precipitation, but its rugged topography and short rivers lead to rapid water runoff into the sea. Consequently, in many regions of Japan, agricultural ponds have served as the primary water reservoirs for irrigating rice paddies. It is estimated that there are approximately 150,000 agricultural ponds in Japan, most of which were constructed over a century ago. This study investigates the impact of climate change-induced shifts in rainfall patterns, as well as demographic changes such as declining birth rates and an aging population, especially in rural areas, on the status of agricultural ponds in Japan. Case studies conducted in various regions indicate that the discontinuation or abandonment of these ponds is primarily driven by reduced demand and the availability of modern irrigation facilities that can access water from larger, more efficient reservoirs compared to nearby agricultural ponds. Notably, small-scale ponds (less than 5,000 m3 in capacity), which constitute the majority of the total pond count, are being phased out due to considerations of utilization and management efficiency. Furthermore, recent increases in heavy rainfall events have underscored the risks associated with agricultural ponds, prompting stakeholders to opt for discontinuation or abandonment. This presentation delves into discussions on sustainable and effective water management, considering the environmental and socioeconomic factors influencing the fate of agricultural ponds in Japan. We also outline the survey methodology used, which emphasizes socio-hydrological aspects, and discuss the data analysis techniques applied to study the extensive number of agricultural ponds.