The 2023 John Dalton Medal is awarded to Taikan Oki for his seminal contribution to global hydrology through pioneering work in developing novel numerical models to quantify the global water cycle, and its evolution under human pressure.
Taikan Oki has made an outstanding and sustained contribution to global hydrology through his pioneering work in developing large-scale hydrological models for climate applications and global water resources assessments. His accomplishments are widespread and influential; he established pioneering concepts such as river routing (Total Runoff Integrating Pathways or TRIP) and hydro-dynamics (CaMa-Flood) that have been incorporated widely into forecast and climate models. With the inclusion of TRIP (and follow-up algorithms) in land surface schemes, the longstanding Dooge problem of how to parameterise a global hydrological model was finally addressed. Oki demonstrates a continuing line of research from modelling global river networks including floodplains, to the hydro-dynamics of river flow and the introduction of human interventions (e.g., reservoirs) in a basin. These are fundamental processes for integrating hydrology (via land surface schemes) into climate models, and vital for closing the water balance in major river basins. Oki is the father of the H08 model, a global-scale integrated water balance model coupling sub-models of reservoir operation, human water withdrawal, environmental flows and crop growth – one of the very first model of its kind. His mentoring of many students, leadership and contribution to the international science community is impressive. He has been a leading hydrological expert in several scientific groups, such as; Global Energy and Water Exchanges/World Climate Research Programme, Global Land-Atmosphere System Studies, Prediction in Ungauged Basins, and the Intergovernmental Panel on Climate Change (IPCC), having contributed to the last three assessments of IPCC as both Lead Author and Coordinating Lead Author.