2026 Water Cycle White Paper | Chapter 8FY2026 Water Cycle White Paper: Chapter 8 Surveys for Policy

To continue advancing water cycle policies appropriately, Japan is conducting water cycle surveys and establishing the systems needed to support them. The chapter covers surveys of basin water quantity and quality, water resources, living organisms, groundwater, and rainwater and reclaimed water use.

The latter part of the chapter covers publication and effective use of survey results, as well as research into climate change impacts on the water cycle and adaptation.

Surveys of virus concentrations in wastewater were used to track infection trends in local areas, and publication of draft guidelines promoted wastewater surveillance efforts. Surveys of agricultural water use helped facilitate water use coordination and related activities.

The drought risk database supported the development of climate change adaptation plans in local areas.

Water quantity and quality surveys included assessments of the effectiveness of real-time tracking of proteins associated with infectious diseases in wastewater, and the compilation, analysis, and publication of water quality survey results for public water bodies and other sites. Implementation of requirements such as notifications when facilities are installed was tracked using reports from prefectures and other entities, and surveys estimating pollutant loads and related measures were conducted in Tokyo Bay, Ise Bay, the Seto Inland Sea, Ariake Sea, and Yatsushiro Sea, among other areas. The surveys also tracked agricultural water intake facilities, intake volumes, and use. Water resource surveys examined the use of various types of water, water resource development, groundwater, rainwater, and reclaimed water use, and drought occurrence. Results were published in the Current State of Japan's Water Resources.

Regular surveys tracked the habitat, growth, and breeding conditions of organisms in rivers and dam reservoirs. These included the national freshwater fish distribution survey and the insect distribution survey, which also covered aquatic insects. At approximately 300 lakes, marshes, coastal areas, and coral reefs under Monitoring Sites 1000, surveys covered plants, waterbirds, fish, benthic animals, corals, and other organisms. For groundwater, activities included monitoring water levels in designated areas, tracking implementation of measures against land subsidence, collecting and analyzing data, and operating and promoting a groundwater database. Surveys also examined the state, purposes, and volumes of use of rainwater and reclaimed water facilities.

Data on precipitation, runoff, water quality, and other measures from 12 forest hydrology research sites, along with snowpack data from heavy snowfall areas in Niigata Prefecture, were made public. A paper summarizing the development method and bias characteristics of bias-corrected national d4PDF dynamical downscaling data was published. System maintenance, inspection, and modification were also carried out to centrally manage and process water quality survey data efficiently.

Climate change surveys examined methods for assessing water resource impacts by river system and region from both demand and supply perspectives, and organized and databased nationwide drought risk analyses conducted with a high-resolution water resource assessment model. A long-term monitoring system was established to assess the effects of forest snow accumulation and melt on water runoff. Observation and future projection information from Climate Change in Japan 2025 was provided, and a symposium was held on weather disaster prevention, drawing on precipitation changes and local response examples. Provision and outreach for Climate Prediction Dataset 2022 and its explanatory guide also continued.

The Extreme Weather Analysis Study Group has operated since 2007. In September 2025, it analyzed and published findings on the characteristics and causes of the record heat that summer and low rainfall in July; in March 2026, it published findings on low rainfall from the latter half of summer 2025 onward. The National Institute for Land and Infrastructure Management conducted runoff analyses in 109 first-class river systems and published changes in the occurrence frequency of low-rainfall years with a non-exceedance probability of 1/10 and drought flows.