Date: Monday, November 30, 2026
Time: 15:50–17:50
Venue: Room 1 (Main Hall)

Theme:
  New Frontiers in Water Cycle Science Through Water Isotopes

Symposium Overview:
Stable water isotopes have long been used as tracers to investigate the origins, movement, and phase-change histories of water across a wide range of disciplines, including hydrology, groundwater hydrology, meteorology, and ecology. In recent years, advances in observational techniques, together with the development of numerical models incorporating water isotopes and isotope data assimilation methods, have greatly expanded their applications—from understanding water cycle processes to improving weather and climate predictions and reconstructing past water cycles. The Conference on Hydraulic Engineering (SUIKO) has also contributed to these developments.

In hydraulic engineering, there has been a tendency to emphasize reproducing observed phenomena, even when the underlying physical mechanisms are not fully understood. However, successfully reproducing observations does not necessarily mean that the processes responsible for those phenomena are correctly represented, nor does it guarantee predictive skill under different conditions. This is the so-called problem of equifinality, which arises when models with many degrees of freedom are constrained by limited observational information. Stable water isotopes offer an important advantage in addressing this problem. Based on relatively well-understood principles of isotopic fractionation and transport, they can provide independent constraints without substantially increasing model complexity. By exploiting this characteristic, researchers have made progress in identifying water cycle processes that could not be distinguished using conventional observations alone and in reducing model uncertainty across a wide range of spatial and temporal scales.

This symposium will review advances in the application of water isotopes to hydrometeorology, groundwater hydrology, and ecology, while highlighting recent findings and future perspectives from early-and mid-career researchers working on paleoclimate reconstruction, large-scale water cycle processes, and weather and climate prediction. Through these presentations and discussions, we aim to explore new opportunities for water isotope research and revisit the importance of understanding the mechanisms underlying observed phenomena, rather than merely reproducing observations. Ultimately, the symposium seeks to discuss future directions in water cycle science that extend beyond the traditional boundaries of hydraulic engineering.

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Program

Chair:
  Kenichiro Kobayashi  (Saitama University, Chair, Subcommittee on Glocal Climate Change Adaptation Research)

Opening Remarks and Introduction:
  Kenichiro Kobayashi (Saitama University,  Chair, Subcommittee on Glocal Climate Change Adaptation Research)

Invited Presentations:
1. Advances in Isotope Hydrometeorology Alongside the Development of Hydraulic Engineering
    Kei Yoshimura (Professor, Institute of Industrial Science, The University of Tokyo)

2. Tracing Groundwater–Surface Water Interactions to Understand Water Cycle Processes
     Maki Tsujimura (Professor, Institute of Life and Environmental Sciences, University of Tsukuba,
                                    Dean, School of Transdisciplinary Science and Design, University of Tsukuba, Malaysia)

3. Isotope Ecology in Catchment Systems
    Ichiro Tayasu  (Professor, Fundamental Research Department, Research Institute for Humanity and Nature (RIHN))

4. Toward an Integrated Framework for Water Isoscapes: Introduction to the Research Network and Recent Advances in Paleoclimate Studies
    Kanon Kino (Lecturer, Institute of Industrial Science, The University of Tokyo)

5. Understanding Japan's Water Cycle Through Water Isotopes: From Seasonal Variability to the Characteristics of the Baiu Rainy Season
    Masahiro Tanoue (Senior Researcher, First Laboratory, Department of Observation and Data Assimilation Research, Japan Meteorological Institute)

6. Advancing Weather and Climate Prediction Using Water Isotopes
    Atsushi Okazaki (Associate Professor, Center for Environmental Remote Sensing (CEReS), Chiba University)

   General Discussion