Concept

Water cycle

Also known as: Hydrologic cycle, Hydrological cycle

The continuous global movement of water between ocean, atmosphere, land, vegetation, and groundwater. The defining circulation of life on Earth. The water cycle is conventionally taught as a single global process — evaporation, condensation, precipitation, runoff — but is more usefully understood as the interaction of two cycles: a 'large' cycle moving water between oceans and continents, and a 'small' cycle locally recycling water within terrestrial ecosystems. Vegetation cover, soil structure, and intact watersheds are the substrate that keeps both cycles functioning; their loss accelerates downstream and downwind drying.

The conventional picture

[[water|The water cycle]] as taught in introductory ecology:

Evaporation from ocean and land surfaces
Transpiration from plant leaves
Condensation in cooler upper atmosphere into clouds
Precipitation as rain, snow, hail, dew
Runoff and infiltration — rain runs over the surface to streams and rivers, or infiltrates into soil and groundwater
Return to ocean through rivers and groundwater discharge

[[death|The cycle]] is closed at planetary scale: total water is approximately constant; the same water molecules cycle through different reservoirs (ocean, atmosphere, ice, soil, groundwater, biota) on timescales from days to millennia.

The two-cycles framing

A more useful working framing distinguishes:

Large water cycle — water moves between oceans and continents through atmospheric circulation. Ocean evaporation → continental precipitation → river return to ocean. [[death|The cycle]] that fills aquifers, rivers, and lakes from atmospheric input.
[[small-water-cycle|Small water cycle]] — water that falls on land is locally recycled through transpiration and condensation, often multiple times, before returning to the ocean. The cycle that operates within a continental landmass, particularly inland and where vegetation is intact. See [[small-water-cycle]].

The two cycles are not separate; they interact and overlap. But conservation work makes the distinction useful: protecting forests inland is about the small cycle; protecting watersheds and coasts is largely about the large cycle.

Reservoirs and timescales

Water resides in different reservoirs for different durations:

Atmosphere — average residence time ~9 days
Rivers — weeks to months
Soil moisture — weeks to months
Lakes — years to centuries
Shallow groundwater — years to centuries
Deep groundwater — centuries to millennia
Ice (glaciers, ice caps) — centuries to hundreds of millennia
Ocean — centuries to millennia at the surface; tens of thousands of years at depth

These different timescales matter operationally: deep-aquifer water depleted today is, for human purposes, gone — refill timescales exceed civilizational planning horizons.

Sources

USGS water-cycle technical materials
Ecology (Begon, Harper, Townsend) — standard ecology textbook treatments
IPCC reports on hydrologic cycle changes

Rooted in life.

What links here, and how

Inbound connections from across the wiki, grouped by lens and by relationship. These appear automatically — every entity page declares what it links to, and that data populates here on the targets.

Scientific

shares approach with

Beaver dam analog BDAs reverse the channel-incising, water-table-dropping pattern of degraded streams; restore meadow-and-wetland hydrology
Watershed restoration watershed restoration restores the small water cycle at landscape scale — local rainfall captured, infiltration restored, base flow returned to streams

substrate of

Riparian buffer buffers are landscape interventions that protect water quality and hydrology — the operational scale at which water-cycle protection happens on agricultural land

Practical