2026 Water Cycle White Paper

The 2026 Water Cycle White Paper was submitted to the 221st extraordinary session of the National Diet. Under Article 12 of the Basic Act on the Water Cycle (Act No. 16 of 2014), it reports the measures concerning the water cycle that the Japanese government took in fiscal 2025. The main text covers cooperation across river basins, groundwater, water storage and recharge, water use, education, public awareness, research, science and technology, and international cooperation, among other topics.

The feature’s full title is “The Water Cycle and Risks: Protecting People’s Lives and the Future.” Its sections are “Section 1: The Effects of Climate Change on the Water Cycle and Daily Life,” “Section 2: The Current State and Challenges of the Water Infrastructure That Supports the Water Cycle,” and “Section 3: Efforts and Public Participation to Protect the Future.” It presents challenges and responses in the order of climate, water infrastructure, and personnel and participation.

The white paper identifies flooding, drought, and effects on groundwater associated with changing precipitation patterns. It also cites the aging of facilities built since the period of rapid economic growth, damage from earthquakes and other events, and shortages of technical staff. It says responses that account for these risks are important if people are to continue benefiting from water and maintain or restore a healthy water cycle.

Extreme heavy rainfall associated with climate change can cause floods that seriously damage homes and other assets, as well as infrastructure. Meanwhile, more days without precipitation, less snowfall and earlier snowmelt, and greater evapotranspiration are expected to reduce river flows and, in some areas, lower groundwater levels. The white paper expresses concern about effects on both flooding and drought.

Rising sea levels and declining river flows may increase how far and how long saltwater moves upstream in rivers, affecting water intake conditions and water use. Saltwater intrusion into groundwater may also affect the tap water of local governments that use it. Higher river water temperatures are projected to shrink coldwater fish habitats, while changes in snowfall and snowmelt are projected to affect river ecosystems.

During the 1994 nationwide drought, water intake from the Tone River system was restricted by as much as 30%. Water shutoffs and other disruptions affected approximately 15.82 million people nationwide, and crop damage reached approximately 140.9 billion yen. The white paper uses this case to show how drought affects society as a whole, including agriculture and industry as well as daily life.

Damage to water infrastructure in the 2024 Noto Peninsula earthquake and a road collapse caused by a broken sewer pipe in Yashio City, Saitama Prefecture, had major effects on people’s lives and industrial activity. The white paper says infrastructure must remain functional, including the provision of a stable water supply, even when a major disaster or accident occurs.

During heavy rain in the Kyushu region in August 2025, flood control by Midorikawa Dam and river improvement lowered the flood water level of the Midorikawa River, which flows through Kumamoto City, by approximately 70 cm. The water stayed approximately 20 cm below the top of the levee, preventing it from overflowing. The white paper presents this as an example of water infrastructure preventing flood damage.

In the water resources sector, research is advancing to clarify the effects of climate change on the water cycle, alongside adaptation and mitigation measures to reduce those effects. The National Institute for Land and Infrastructure Management conducted runoff analyses of 109 major river systems nationwide and published changes in the frequency of low rainfall years and drought flows. The Ministry of Education, Culture, Sports, Science and Technology’s advanced climate change prediction research program is also examining the development of the next Climate Prediction Dataset.

As a flood control adaptation measure, revisions to the Basic Policy for River Improvement are proceeding in light of projected increases in rainfall and basin flood control. For each river system, the national government, basin municipalities, companies, and others work together to bring river improvements, advance releases from water supply dams, rice paddy dams, rainwater storage and infiltration facilities, and land use regulations into basin flood control projects. To prepare for drought, stakeholders estimate potential damage and create drought response timelines.

During the summer drought of 2025, drought response timelines were created for 16 river systems that entered drought response status. In the Naruko Dam basin, rainfall from June through August totaled just 219 mm, the lowest amount in the past 30 years, and the reservoir storage rate reached 0% on July 29. To supplement agricultural water supplies, officials used stored water below the minimum water level through an emergency drought release and released water from Gandosawa Dam.

For water supply systems, sewers, levees, dams, and other facilities, strategic maintenance through preventive care and stronger disaster resistance, including seismic upgrades, are being advanced under the First Medium-Term Implementation Plan for National Resilience. Following the Yashio City accident, the frequency and methods of sewer pipe inspections and the management of underground pipelines are under review. A shift in management based on two forms of targeted prioritization and two forms of greater visibility has been proposed.

Because well water, spring water, and rainwater served as alternative water sources in areas affected by the Noto Peninsula earthquake, efforts are advancing to support local governments in using emergency wells and springs during disasters. The Guidelines for Groundwater Use During Disasters: Toward the Use of Emergency Wells and Springs were revised in 2025 to provide more detailed procedures for considering and developing new wells.

The second report of the Study Group on the Basic Direction of Water Supply and Sewerage Policy states the need to promote integrated business operations by multiple municipalities, through business consolidation or integrated management, so that they jointly manage and operate personnel, facilities, and funding. The Ministry of Land, Infrastructure, Transport and Tourism says it will examine and implement measures to advance wider regional cooperation, including integrated business operations, under national leadership.

As of 2025, the number of municipal civil engineering staff was 26.4% below its 1996 peak. The white paper expresses concern about shortages of personnel to operate, maintain, and renew water infrastructure and to conduct research and technology development, and it emphasizes adopting digital technology. In the water supply and sewerage sector, standardized implementation of maintenance technology nationwide is advancing through common work processes, standardized information management, wider use of digital transformation technology, and visualization of current conditions.

To share a basin’s challenges, future vision, and measures among stakeholders, local governments and others are establishing basin water cycle councils and developing basin water cycle plans. The Cabinet Secretariat’s Water Cycle Policy Headquarters Secretariat registers and certifies company initiatives that contribute to the water cycle. It supports the continuation and expansion of those initiatives by listing them on a portal, matching companies with local governments and organizations, and providing information.

As examples of basin management, the report describes groundwater conservation in Ono City using residents’ groundwater level observations and research findings; learning sessions and community activities centered on Sayama Pond in Osakasayama City; and waterfront activities in the Inba Lake basin coordinated by municipalities, private businesses, and others. The feature shows how government bodies, experts, businesses, and residents work together in ways suited to local natural conditions and challenges.

The main text includes chapters on “Promoting Cooperation Across River Basins: A Framework for Comprehensive and Integrated Basin Management,” “Appropriate Conservation and Use of Groundwater,” “Maintaining and Improving Water Storage and Recharge Functions,” and “Promoting Appropriate and Effective Water Use.” It then covers education and personnel development, public awareness, voluntary activities by private organizations and others, research, science and technology, international coordination, and international cooperation, setting out the scope of government measures.