Panta Rhei: Coevolutionary change in hydrology and society

This chapter introduces the Panta Rhei initiative—“Everything Flows”—as a new IAHS decadal focus on the coevolution of coupled human-water systems. Drawing on three illustrative case studies from Indus Basin irrigation, Vienna’s Danube flood defenses, and Cape Town’s water-equity crisis, it demonstrates how bidirectional feedback between social and hydrological processes gives rise to emergent phenomena—often in the form of unintended consequences such as the levee effect, reservoir rebound, and groundwater depletion. By moving beyond stationary, scenario-based paradigms, the chapter argues for a longer-term, coevolutionary perspective that explicitly models human-water interactions, recognizes the potential for tipping points, and integrates both natural and social science insights.