[News] Continued Water Intake Restrictions in the Tone River System
1. Current Status of Continued Water Intake Restrictions in the Tone River System
10% Restriction on the Kanna River and Decline in Dam Storage Rates
From 9:00 AM on May 26, 2026, a 10% water intake restriction for agricultural and industrial use was initiated on the Kanna River, a tributary of the Tone River system. This measure was announced by the Takasaki Office of River and National Highway of the Kanto Regional Development Bureau, and the direct cause is that the water storage level of the Shimokubo Dam, located in the Kanna River basin, has dropped to a critical level. According to data as of June 18, 2026, against the effective capacity of 120 million cubic meters of the Shimokubo Dam, the water storage is approximately 38.98 million cubic meters, with a storage rate remaining at only 32%.
The Shimokubo Dam is located in an area where recovery of water storage through snowmelt runoff cannot be expected, and it has the characteristic that its water storage situation is greatly influenced by rainfall. Looking back at the situation in 2026, rainfall from August to October 2025 was below average, which increased supply to the downstream areas and caused a significant decrease in water storage. Subsequently, there was almost no rain around the dam from December to January, and the early summer arrived without the water storage recovering sufficiently. Although a slight recovery was seen due to Typhoon No. 6 in June, it did not reach the amount of water required to lift the intake restrictions, and the status quo is being maintained. The following image shows the current state of the area around the Kanna River where water intake restrictions are being implemented.
Water Storage Status of the 9 Dams in the Upper Tone River and the Role of the Yamba Dam
Although water intake restrictions are not currently being implemented on the main stream of the Tone River, the overall water storage status of the 9 upstream dams is at a stage that does not allow for optimism. As of June 18, 2026, the total water storage of the 9 dams is approximately 278.88 million cubic meters, with a storage rate of 51%. This is a level of approximately 77% compared to the past average from 1992 to 2025, and water storage is decreasing at a pace significantly lower than average years. In particular, decreases at major dams such as the Yagisawa Dam (51% storage rate) and the Sonohara Dam (44%) are notable.
What is noteworthy in this drought situation is the existence of the Yamba Dam, which began full-scale operation in 2020. The storage rate of the Yamba Dam as of June 18, 2026, is 46%, and it is playing a role in bolstering the water storage of the entire Tone River system. It is estimated that if the Yamba Dam did not exist, the water storage of the entire river system would have fallen into an even lower situation. However, the fact that it is below the average even with the operation including the Yamba Dam suggests that this water shortage is widespread and serious. Please refer to the following graph for the transition of water storage in the dam group.
Crisis of Drought Adjustment Approaching the Kinu River System
In the Kinu River, which is a powerful tributary of the Tone River system, the risk of drought is also rising rapidly. As of June 18, 2026, the total water storage of the four upstream Kinu River dams—Ikari Dam, Kawamata Dam, Kawaji Dam, and Yunishigawa Dam—has dropped to 112.66 million cubic meters, a storage rate of 55%. This means that it has decreased to a level equivalent to 2013 and 2016, when water intake restrictions were implemented in the past. Although the storage rate was a healthy 89% as of April, the water storage has decreased by approximately 114 million cubic meters in just two months, and it is characterized by a faster rate of decrease than the main stream of the Tone River.
In response to this situation, extraordinary meetings of the "Kinu River Water Utilization Coordination Liaison Council" and the "Kinu River Upstream Water Utilization Coordination Liaison Council" were held on June 18, 2026. In the Kinu River, there is a track record of implementing a maximum 10% water intake restriction from July to September in 2024. Depending on future rainfall conditions in 2026, there is a very high possibility that drought adjustment will be implemented for the Kinu River alone ahead of the main stream of the Tone River. In particular, since the Kawaji Dam and Yunishigawa Dam also serve the purpose of water utilization for the entire Tone River system, a decrease in water storage here may affect the water supply and demand balance of the entire metropolitan area.
2. Background to the Serious Water Shortage in the Summer of 2026
Impact of Record-Breaking Low Snowfall and Premature Snowmelt
The biggest natural factor that caused the drought in 2026 is the extreme "low snowfall" in winter and the accompanying "premature snowmelt." The dam group in the upper reaches of the Tone River is designed to recover to near full capacity with spring snowmelt water (snowmelt runoff) in normal years and supply that water during the period from May to June when demand for agricultural water is high. However, in 2026, the time when snowmelt ended was about one month earlier than in an average year, and the supply of snowmelt water was significantly insufficient.
Looking at specific observation data, the maximum snow depth at the Fujiwara point in Gunma Prefecture on April 1, 2026, was only 2 centimeters. This is the second lowest record in the past 27 years from 1990 to 2026, following 2020. Compared to the fact that there was 131 centimeters of snow at the same time in the previous year, 2025, it is clear how little snow there was in 2026. Due to this, it became necessary to supply water to the downstream areas, which could normally be covered by snowmelt water, by depleting the dam's water storage, resulting in a sharp drop in the storage rate before summer. The following figure is comparison data of snow depth in April in recent years.
Prolonged Low Rainfall Trend and Deterioration of Meteorological Conditions
In addition to low snowfall, the lack of rainfall that has continued since the second half of 2025 is also casting a serious shadow. The average precipitation in the upper reaches at the Kurihashi point of the Tone River has continued to fall below the past average in many months since June 2025. This trend has been particularly notable since entering 2026, with January precipitation remaining at about 50% of the average (21 mm), and February also remaining at about 40% of the average (19 mm) as of the 26th.
Also, the start of the rainy season was confirmed nationwide around June 20, 2026, but sufficient rainfall from the rainy season front has not been brought to the upper reaches of the dams. Under drought conditions, continuous rain that falls over the entire catchment area of the dam is required, not localized thunderstorms, but the 2026 rainy season is currently continuing in a state close to a dry rainy season. Regarding temperature, the probability of it being "high" in the forecast for the next month is 50%, and concerns have arisen that the increase in water demand accompanying the rise in temperature will further pressure water storage. Please refer to the following graph for the transition of water storage in the dam group.
3. Social Impact and Future Measures
Risks to Industrial and Economic Activities and Requests for Water Conservation
The continuation and strengthening of water intake restrictions have a significant impact on regional industries and economic activities. Especially for manufacturing and semiconductor industries that use large amounts of industrial water, concerns over water supply pose a direct risk of shortened operations and reduced product quality. Past surveys have shown that when water intake restrictions exceed 20%, the number of businesses forced to deal with impacts on production equipment or operational shutdowns increases sharply, leading to heightened anxiety over the potential for the current 10% restriction to be further tightened.
Furthermore, in the agricultural sector, water shortages during the critical period after rice planting can lead to poor crop growth and reduced yields. Referring to a past emergency survey conducted by the Toyohashi Chamber of Commerce and Industry, approximately 35.8% of responding businesses require water as a fundamental part of their operations, and about half of these businesses anticipate some form of management impact if water conservation measures are prolonged. The administration is calling on citizens to voluntarily conserve water in their daily lives, and is currently at a stage of reducing the burden on society as a whole, such as by suspending water sprinkling at public facilities and restricting the use of swimming pools.
Timeline Operation by the Drought Countermeasure Liaison Council
In response to the worsening drought, the Ministry of Land, Infrastructure, Transport and Tourism is rushing to coordinate with relevant prefectures through the "Tone River System Drought Countermeasure Liaison Council." This council is composed of the Kanto Regional Development Bureau of the Ministry of Land, Infrastructure, Transport and Tourism, the Ministry of Economy, Trade and Industry, the Ministry of Agriculture, Forestry and Fisheries, and one metropolis and six prefectures including Tokyo, and serves as an organization for information sharing and coordination among water users. Currently, specific actions are being taken based on the "Drought Response Timeline," which defines measures according to the situation from the initial stage of drought to its intensification.
Specifically, to prevent the water storage situation from shifting from Category 1 (start of water intake restrictions) to Category 2 (serious impact on socio-economic activities), flexible operation of dams and, if necessary, water diversion from other river systems are being considered. In addition, in preparation for abnormal droughts, requests for cooperation from power generation companies to divert dam capacity dedicated to power generation for municipal water use have also been manualized. An extraordinary meeting of the steering committee is scheduled for June 24, 2026, and whether an increase in water intake restrictions or new measures will be presented there is a major focus.
4. Future Outlook and Points of Attention
Future Policy and the Direction of Water Intake Restrictions Indicated by the Extraordinary Meeting
The results of the "Tone River System Drought Countermeasure Liaison Council Steering Committee (Extraordinary)" scheduled to be announced on June 24, 2026, will have a decisive impact on water usage in the Tokyo metropolitan area this summer. At this meeting, the latest water storage data and weather forecasts will be compared to discuss whether to continue the current 10% water intake restriction or to expand the target areas or restriction rates. In particular, if the water storage rate of the Shimokubo Dam does not recover, the possibility that water intake restrictions will be introduced in the main river basin other than the Kanna River cannot be denied.
In addition, the judgment at this steering committee meeting regarding the start of drought adjustment in the Kinugawa River system is also attracting attention. The council will discuss how to maintain the balance of demand for each water user (agricultural water, industrial water, and municipal water) while viewing the situations of the Tone River and the Kinugawa River in an integrated manner. For citizens and companies, based on the outlook presented at this meeting, further water conservation measures and a review of operational plans may become necessary.
Prospects for Resolution Based on Typhoon Paths and Three-Month Forecasts
The biggest uncertain factor influencing the future situation is the formation and path of typhoons. Typhoon No. 7, which formed on June 20, 2026, is approaching the Okinawa region, and the key will be how much rainfall this typhoon and the subsequent tropical depressions bring to the upper reaches of the dams. In recent cases, even in years with little snow, there have been instances where water storage levels recovered dramatically due to rainfall from typhoons after August, allowing for the avoidance of serious drought.
However, according to the three-month forecast (and subsequent long-term outlook) from March to May 2026 released by the Japan Meteorological Agency, the probability of precipitation over the next few months being "below average" or "average" exceeds 70% in total, so the situation is not one where natural recovery can be viewed with optimism. Since temperatures are also predicted to remain high, it is necessary to prepare for the risk of prolonged water intake restrictions toward August, when increased evaporation and peak water demand coincide. It will be a summer that requires cooperation across the entire region, while keeping a close eye on government announcements and real-time water source information.
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