Fields, Dams, and the Sea—The Same Cause Unites Three Locations

This summer in Hiroshima has wreaked havoc across three different locations simultaneously.

In the fields of Nishi Ward, Hiroshima City, the traditional vegetable “Kan-on Negi” has been completely wiped out. At the Haizuka Dam in Miki City, over 10,000 sweetfish were found floating. Meanwhile, along the Seto Inland Sea coast, the harvest of Hiroshima oysters has halved compared to the same period last year, causing the region to relinquish its top position in national production.

Fields, freshwater areas, and the sea—these locations are disparate, with different crops and creatures. However, when we line up these three sites, the same physical conditions emerge. Extreme heat, drought, and rising water temperatures. When the balance of “heat” and “water” that constitutes the water cycle of the Seto Inland Sea is disrupted, the region’s primary industries are shaken not individually, but structurally—this is what this summer in Hiroshima has demonstrated.

—

Total Loss of Kan-on Negi—Water in the Soil Disappeared

Kan-on Negi is a traditional vegetable that has been cultivated in the Kan-on district of Hiroshima City since the Edo period. It is known for its soft leaves and strong sweetness. The soil and moisture of the alluvial plains near the mouth of the Ota River have supported the flavor of this variety.

In the summer of 2023, Hiroshima City experienced rainfall in July that was less than 30% of the average, with consecutive days of extreme heat exceeding 35°C. The soil moisture necessary for cultivating Kan-on Negi rapidly diminished. For small-scale farmers lacking sufficient irrigation facilities, these conditions proved fatal. Reports indicate that in some fields, all the plants have withered, resulting in a state described as “total loss.”

One producer reportedly said, “If only we had water, we could have held on. If it had rained a little earlier…” This statement carries a quiet recognition that they have entered a stage where technology and effort can no longer suffice. For farmers with annual sales in the hundreds of thousands of yen, the total loss of a single crop shakes the very foundation of their business. Moreover, Kan-on Negi is a variety that relies on seed collection for the following year. A total loss threatens not only this year’s harvest but the very cultivation base for years to come.

The essence of the problem lies not solely in the extreme heat as a “natural disaster.” What has supported the cultivation of Kan-on Negi is the groundwater of the Ota River system and the humid climatic conditions at the estuary. The decline in groundwater levels due to urbanization and changes in the watershed’s water retention capacity—these long-term structural changes have been compounded by this year’s extreme heat. It should be understood that an extreme burden has been placed on a system that was quietly weakening.

—

Death of 10,000 Sweetfish—Water Temperature in the Dam Exceeded 30°C

The Haizuka Dam in Miki City is a multipurpose dam built on the Washigawa River of the Enokawa system, known for flood control and water supply, as well as being a popular spot for sweetfish fishing. In the summer of 2023, the water temperature in this dam reached 30°C, leading to the mass death of over 10,000 sweetfish.

The ideal water temperature for sweetfish is generally between 10 and 20°C. A temperature of 30°C greatly exceeds their survival limit. Additionally, as water temperature rises, the amount of dissolved oxygen in the water decreases. Fish are simultaneously confronted with conditions that are “hot” and “lack oxygen.”

The dam’s water storage level fell below 60%, raising concerns about water intake restrictions. As water volume decreases, the water depth becomes shallower, further accelerating heating from sunlight. The reduction in water and the increase in temperature are not independent issues but accelerate each other—this vicious cycle has intensified in the closed water area of the dam.

Fishing for sweetfish at Haizuka Dam is also a tourism resource that attracts visitors from autumn to winter. A drastic reduction in the resource due to mass deaths will directly impact visitor numbers in the fall and beyond. For the dam’s managers, fishing cooperatives, and tourism stakeholders, the variable of water temperature is creating ripples across various interests.

It is noteworthy that Haizuka Dam is a “multipurpose dam.” With multiple functions such as flood control, agricultural water supply, industrial water supply, and power generation, decisions must be made during droughts about which water use to prioritize. Releases to protect the sweetfish habitat may compete with other water supply purposes. Thus, this issue is not merely about fish deaths; it relates to the design of the water resource allocation system.

—

Halving of Oyster Harvest—The Significance of Falling from First to Second Place

Hiroshima Prefecture’s oyster farming has accounted for about 60% of the national share. The recognition that “Hiroshima means oysters” is deeply rooted in both tourism and food culture. However, according to statistics from the Ministry of Agriculture, Forestry and Fisheries, the harvest of Hiroshima oysters from July to December 2022 halved compared to the same period the previous year, causing Hiroshima to drop to second place in the national production ranking.

Oyster farming is greatly influenced by seawater temperature and the amount of phytoplankton available as food. The Seto Inland Sea is a semi-closed water area and is more susceptible to temperature fluctuations compared to the open sea. High summer water temperatures increase the mortality rate of oysters while simultaneously altering the composition of plankton. Furthermore, a decrease in freshwater inflow from rivers changes the salinity and nutrient balance of the seawater.

In other words, the poor harvest of oysters is not solely a problem of the sea. Rain that falls on the mountains flows down rivers and enters the sea along with nutrients—drought occurring upstream may impact the productivity of the downstream sea. The water shortage that dried up the Kan-on Negi and the changes in the sea that reduced oyster populations can be viewed as phenomena occurring in the upstream and downstream of the same water cycle.

The economic impact on oyster producers is enormous. The output value of Hiroshima’s oyster farming is estimated at 20 billion yen annually, and a halving of the harvest will have a ripple effect on processors, distributors, restaurants, and the tourism industry. The significance of the potential disruption to Hiroshima’s food identity, which includes okonomiyaki, cannot be measured solely by economic indicators.

—

A Single Structure Indicated by Three Locations

Kan-on Negi, sweetfish, and oysters—when we line up these three damages, what becomes clear is that the single structure of the “Seto Inland Sea water cycle” is simultaneously crying out at multiple outlets.

Rain falling in the mountains becomes groundwater, flows through rivers, accumulates in dams, and pours into the sea. Along the way, it nourishes farmland, supports freshwater fish, and replenishes the nutrients in the sea. If any part of this cycle becomes clogged, everything downstream is affected. What happened in Hiroshima in 2023 can be seen as a case that simultaneously visualizes what occurs when the “entry point” of that cycle—precipitation—is drastically reduced across three different locations.

Individual producers are enduring the heat, managing their water supplies, and trying to hold on. Their efforts are undeniable. However, the range of fluctuations that individuals can absorb is beginning to be exceeded by the climate’s variability. Therefore, the question should not be “Who can work harder?” but rather, “What system can be changed to reduce the burden on the field?”

Options for countermeasures have already been discussed, including large-scale management of water resources, revising allocation rules for agricultural and environmental water, establishing seed banks for traditional varieties, and monitoring systems for aquaculture areas. The problem is that these measures are still scattered as individual policies. The issues in the fields pertain to agricultural policy, the issues with the dam relate to the Ministry of Land, Infrastructure, Transport and Tourism, and the issues at sea concern the Fisheries Agency—these vertical divisions of jurisdiction do not align with the horizontal structure of the water cycle.

—

Whose Comfort Is This Question For?

The phrase “Let’s be conscious for a sustainable future” is correct but feels somewhat distant.

There is a more immediate question. Will we be able to sow Kan-on Negi seeds again next year? Will fishing customers return to Haizuka Dam? Will there be winter jobs for those working in the oyster processing industry?—The answers to these questions lie not in consciousness but in systems.

The flow of water is a single connection from the mountains to the sea. Those who have built their lives upon that flow are now facing difficulties simultaneously. Viewing the three locations as a single structure—this is the first step toward considering the next move.

The hands that touch the soil in the fields, the water level gauges in the dam, and the rafts floating in the sea. Each of these locations may seem distant, yet they all exist upon the same water.