Supporting commission(s) / organisations: IAHS transversal, Panta Rhei, UNESCO-IHP

The Anthropocene was originally proposed as a geological epoch, and is still under consideration in the strict field of stratigraphy. Yet, whatever will be the conclusion of the stratigraphic commission of IUGS about the formal adoption of a new geological epoch, and the date of its starting, the Anthropocene has broadened through the biophysical and social sciences into an integrative concept that covers human-environment interactions and impacts. Change has reached the planetary level, not only through accumulation but also through the emergence of systemic symptoms of high magnitude and notable simultaneity and synchronicity. All aspects of these changes correspond to risk and security issues for shorter or longer-term futures, from the magnitude of some processes, to unperceived connections, and to crossings of planetary boundaries. Water plays crucial roles in the Anthropocene as a geological and geomorphological driver, as a biogeochemical agent, as a vital and economic resource, as an energy storage and vehicle. Furthermore it follows hydrological dynamics which then drive other related dynamics or properties (ecology, food, health, energy, settlement, land use including agriculture and urbanization, infrastructures and logistics) and poses multidimensional security issues. These hydrological dynamics are themselves naturally complex across a wide range of scales and variabilities, and determine many topological, geometric, temporal, frequency and interdependence structures (meteorological and climatological space-time organizations, oceanic and cryospheric driving roles, upstream-downstream relationships, ground-surface-atmosphere exchanges, land-lake-sea interfaces, virtual water footprint and trade, hazard and related perception-vulnerability-resilience). Depending on strong coevolutions, these natural hydrological dynamics and related dimensions of complexity are often strongly modified by anthropogenic effects. Hydrological sciences must thus contribute to the assessment of the water-related dimensions of the Anthropocene ongoing transformation, and ultimately to the prospective challenges as described in the SDGs framework.