Tojiro Ishihara
Contents
Photograph[edit]
Dates[edit]
Tojiro Ishihara, 26.08.1908 - 02.10.1979
Biography[edit]
Tojiro Ishihara was a Japanese civil engineer and hydrologist from Kyoto Prefecture, Japan. He graduated from the Department of Civil Engineering, Kyoto Imperial University, in 1930, and later served as lecturer and associate professor before becoming full professor in 1943. He retired in 1973 and subsequently joined Nihon University, where he held posts such as Dean of the Faculty of Science and Engineering, Director of the Institute of Disaster Prevention, and Director of the Large-scale Computer Center. He also served as a member and Section V Director of the Science Council of Japan, Chairman of the Organizing Committee of the International Association for Hydraulic Research conference, and President of the Japan Society of Civil Engineers (JSCE).
Hydrological Achievements[edit]
Ishihara played a central role in both the institutionalization of modern hydrology in Japan and the advancement of flood and runoff analysis. In the aftermath of World War II, together with Shigehisa Iwai at Kyoto University, he emphasized the urgent need to systematize hydrology for Japan’s postwar reconstruction. In 1946, they proposed dividing hydrology into four fields: meteorology (atmospheric water phenomena), hydrology (surface water phenomena), hydrography (graphical methods for river planning), and hydrological statistics (statistical analysis of hydrological data).
At the same time, Ishihara advanced the field of hydrological statistics and probabilistic flood analysis, highlighting the need to evaluate the safety levels of Japan’s major rivers. He recognized the limitations of applying the conventional unit hydrograph to Japan’s steep, small basins and pioneered new runoff analysis methods based on the kinematic wave equation. In 1959, together with Takasao, he derived rainfall–runoff relationships from kinematic wave theory, and in 1962 he conducted Japan’s first empirical rainfall–runoff analysis of a real river basin using this approach. In 1963, Ishihara and Takasao proposed a model that integrated surface and subsurface flow on hillslopes, an early precursor to the variable source area concept. These studies provided a foundation for later distributed runoff modeling using digital elevation data and exerted lasting influence on flood prediction and disaster prevention science in Japan.
Reference Material[edit]
Nakamura, S. et.al., 2025. “Emergence of, and Developments in, Hydrology (Suimongaku) in Japan from the Late 19th Century to 1970.” Hydrological Sciences Journal.
Japan Society of Civil Engineers. “List of Past Presidents.” (in Japanese).
Selected Publications[edit]
Ishihara, T. and Takasao, T., 1963. A study on runoff pattern and its characteristics. Disaster Prevention Research Institute Bulletin, 65, 1–23.
Ishihara, T. and Iwai, S., 1946. Suimon gaku – suimon zu gaku – suimon tōkei gaku. Doboku Gijutsu, 1 (4), 10–16. (in Japanese).
Ishihara, T. and Takasao, T., 1959. Fundamental researched on the unit hydrograph method and its application. Transactions of the Japan Society of Civil Engineers, 1959 (60), d1–d34. doi:10.2208/jscej1949.1959.d1. (in Japanese).
Ishihara, T., et al., 1962. A study on the runoff characteristics of Yura River basin. Disaster Prevention Research Institute Annuals, 5 (A), 147–173. (in Japanese).
