Syukuro Manabe’s Contributions to the Hydrologic Sciences: A Land Model Development Perspective

While Syukuro Manabe’s contributions to climate science are well known, his foundational contributions to the hydrologic sciences are equally noteworthy, though perhaps less frequently celebrated. In 1969 Manabe published the first computational representation of the coupled global water and energy cycles, derived from basic physical principles, with no external forcing other than solar radiation. Central to this achievement was a numerical depiction of the controls on the land water and energy balances—the first land model embedded in a global climate model. Through his simple soil moisture “bucket,” Manabe captured the essential role of land in the Earth system: regulating the partitioning of water and energy fluxes at the surface. Manabe and his colleagues needed this flux partitioning capability to depict the global hydrologic cycle so they could answer what is now recognized as the central climate question of the day: how does global mean temperature change with increasing atmospheric greenhouse gas concentrations? While that simple bucket remained at the heart of land models for decades, modern models have evolved to include surface heterogeneity, dynamic vegetation, and a growing list of human interventions in the Earth system (e.g., irrigation), providing today’s climate modeling community with the tools to answer a new suite of questions that require both a more nuanced treatment of the controls on water and energy partitioning and a fully coupled carbon cycle.