Water & Earth systems
Hydrological Cycle
Definition
The hydrological cycle is the continuous circulation of water between stores — oceans, atmosphere, land surface, ice, and groundwater — through fluxes including evaporation, evapotranspiration, condensation, precipitation, runoff, infiltration, and groundwater flow. Solar energy and gravity drive the cycle; human withdrawals, dams, land-use change, and climate change now measurably alter where water is stored and how it moves.
References
definition and human influence
Overview
What it means
The cycle is finite and closed: water used in one place is unavailable in another, and every sustainability water issue — scarcity, flooding, aquifer depletion, ecosystem flows — is a disruption of some part of it. Climate change intensifies the cycle, making wet events wetter and dry spells drier, which is why water management is often called the front line of climate adaptation.
How it is used
The concept underpins water-resource management, watershed planning, climate-impact assessment, and water-footprint accounting.
Why it matters
Every downstream term in this dictionary — water stress, groundwater recharge, drought — is a chapter of this one cycle.