2026 Water Cycle White PaperChapter 9: Advancing Science and Technology

To continue advancing water cycle measures appropriately, it is considered essential to continually acquire scientific knowledge from diverse perspectives on water. Building on the latest science and technology and past research, the policy is to conduct research and surveys in collaboration with research institutions and academic societies, disseminate findings, and train researchers. It is also considered important to make effective use of data, analysis results, research findings, and other outputs obtained through surveys, including by making them available as open data in clear, accessible formats.

This chapter covers research and surveys on basin water cycles, groundwater, rainwater, effective water use, the water environment, global observation, and the effects of climate change on the water cycle. For each field, it describes analysis of observation data, development of models and forecasting methods, technology demonstrations, and publication or sharing of survey results, and concludes with effective use of research findings.

The National Agriculture and Food Research Organization (Institute for Rural Engineering) developed a numerical model based on a nationwide river network prepared at 1 km resolution. The model integrates information on major agricultural water infrastructure, including dams, headworks, and irrigation canal networks, with agricultural water demand estimated from land use data and other sources. It represents water supply and demand together and provides a basis for visualizing supply-demand pressures and drought risks across different spatial scales: river systems, facilities, and irrigation districts. The Forestry and Forest Products Research Institute of the Forest Research and Management Organization and others continued hydrological observations in forested watersheds and developed forest runoff models under various climate conditions to forecast the effects of forest change and climate change on water resource availability. For trace chemicals and pathogenic organisms in raw and tap water, they examined occurrence, reduction technologies, and monitoring and analysis methods, and comprehensively assessed water quality risks. They also considered reducing risks and strengthening safety across the water supply system by setting management targets and applying scientific findings to ongoing reviews of drinking water quality standards.

In light of social challenges such as large-scale disasters and reducing drought risks, the Research and Development and Society 5.0 Bridge Program (BRIDGE) advanced development of groundwater flow analysis methods for model regions and a simplified model that does not require detailed physical properties of the ground, based on the three-dimensional water cycle model developed under the Strategic Innovation Promotion Program (SIP). The Forestry and Forest Products Research Institute and others analyzed accumulated observations, including runoff data, from forest hydrology test sites and assessed the effects of changes in forest vegetation on runoff during droughts.

Advanced examples of rainwater use were publicized at a seminar for local government staff on rainwater use in fiscal year 2025. Participants also visited rainwater use facilities at public facilities and exchanged information with stakeholders. To broadly collect, analyze, and publish information on rainwater use methods and effects, the survey of rainwater and reclaimed water use facilities continued in fiscal year 2025, and information on facility locations nationwide and rainwater uses was published. In addition, participants visited facilities in Utsunomiya City and private-sector facilities. Officials from the national government, local governments, and rainwater-related organizations took part in research on water quality protection, runoff control, maintenance and management technologies, and facility standards. The effects of controlling concentrated rainwater runoff, maintenance and management, and facility standards were also subjects of research.

The Water Supply Information Utilization System enables flexible, cross-cutting use of equipment and device information held by water utilities and data from administrative systems. Utilities and others adopting the system received support through the Project to Promote Integrated Efficiency and Strengthen the Foundations of Water Supply and Sewerage, and information sessions were held for utilities considering adoption. In the water supply sector, smart meters are expected to improve user services and energy efficiency in addition to streamlining meter reading. Support was provided for introducing advanced technologies through model projects, and officials participated in and advised the industry-government-academia New-Smart Project. Under the Integrated Innovative Technology Demonstration Project for Water Supply and Sewerage (AB-Cross Project), demonstrations advanced for technologies expected to reduce electricity consumption while maintaining stable treated water quality.

The Institute for Rural Engineering analyzed long-term water quality monitoring data from an observation well on the Shirasu plateau of the Osumi Peninsula in Kagoshima Prefecture. It found that groundwater quality recovery from nitrate nitrogen pollution caused by livestock nitrogen loads takes much longer than the progression of the pollution process. The Forestry and Forest Products Research Institute and others analyzed the movement of water and nutrients in forested watersheds and long-term trends to clarify the effects of climate change and forest management on forest water environments. In view of population decline and future disasters, demonstration projects for decentralized systems and downsizable technologies were also advanced to help build resilient and sustainable water supply and sewerage systems.

At the 20th GEO Plenary held in Rome in May 2025, participants presented the development of an early warning system for floods using Earth observation data and related capacity building. The 17th Asia-Oceania Group on Earth Observations (AOGEO) Symposium was held in Bangkok in October of the same year. Following discussions in a special session on the ecosystem for sustainable rice farming and in task groups, including the Asia Water Cycle Initiative (AWCI), participants adopted the “2025 AOGEO Statement.” The statement described the importance of cross-sectoral cooperation to address challenges in the region, including those related to the water cycle.

The Japan Aerospace Exploration Agency (JAXA) advanced observations using Earth observation satellites. These included the Advanced Land Observing Satellite-2, Daichi-2 (ALOS-2, launched in May 2014); the Advanced Land Observing Satellite-4, Daichi-4 (ALOS-4, launched in July 2024); the Global Change Observation Mission-Water, Shizuku (GCOM-W, launched in May 2012); the Global Precipitation Measurement Core Observatory (GPM Core Observatory, launched in February 2014); the Global Change Observation Mission-Climate, Shikisai (GCOM-C, launched in December 2017); the Earth Clouds, Aerosols and Radiation Explorer, Hakuryu (EarthCARE, launched in May 2024); and Ibuki GW (GOSAT-GW), equipped with the Advanced Microwave Scanning Radiometer 3 (AMSR3) and launched in June 2025. Using the Global Satellite Mapping of Precipitation (GSMaP), which combines data from multiple satellites with the GPM Core Observatory at its center, global precipitation information was provided to users in 163 countries and regions worldwide as of the end of March 2026. To further advance this work, development of the Precipitation Measuring Mission (PMM) satellite to follow the GPM Core Observatory and the priority satellite Earth observation theme “Water-Related Disasters and Water Resource Management” were also promoted.

As its fourth year of research under the plan for achieving the medium- to long-term objectives beginning in fiscal year 2022, the Public Works Research Institute advanced development of technologies for sustainable water resource and water environment management under climate change. It continued developing forecasting technologies for the effects of changes in basin water cycles on river water temperatures; water quality changes during droughts and river ecosystems; effects of changes in flow on water quality in rivers with a high proportion of treated sewage; eutrophication in lakes and dam reservoirs; and the nutrient supply effects of treated sewage on coastal areas experiencing nutrient depletion. The Institute for Rural Engineering set the available capacity of basin dams and the implementation rate of “paddy field dams” in rice paddies as adjustable parameters, and clarified how use conditions for facilities and simultaneous use of multiple facilities reduce peak runoff during flood events. It also developed a system to support operation of agricultural facilities by showing real-time observations of drainage channel water levels, overflow, and flooding, and forecasting conditions several hours ahead from recent water level data.

Under the Data Integration and Analysis System (DIAS) project, the Data Integration and Analysis System stably accumulated, integrated, analyzed, and provided Earth environment data, including observations and forecasts. Research and development to help address global challenges such as climate change and disaster prevention continued, and provision of a nationwide probabilistic flood discharge dataset began. The Advanced Studies of Climate Change Projection program advanced climate model development, clarification of impacts on the water cycle, and production of climate projection data to contribute to the IPCC Seventh Assessment Report. It also clarified that global warming contributed to the heavy rain centered on Kumamoto Prefecture in August 2025 and the record-breaking summer heat, and announced the findings to the press in September of that year.

To make effective use of research findings, the Forestry and Forest Products Research Institute published data on precipitation, runoff, water quality, and other topics, and shared it with educational institutions and private organizations. Publication continued of nationwide information on the locations and uses of rainwater facilities, based on the survey of rainwater and reclaimed water use facilities. For groundwater, BRIDGE advanced development of groundwater flow analysis methods and a simplified model based on the three-dimensional water cycle model developed under SIP.