HT1.1 5.1a,b

Global Hydrological Cycle

The global movement of water as a closed system driven by solar energy and gravitational potential energy, involving processes, stores, and flows of water.

Closed System

A system that exchanges only energy and keeps matter within its defined boundaries.

Open System

A system that allows for the transfer of both energy and matter between the system and its surroundings.

Stores

Various reservoirs where elements like carbon or water are held. In the hydrological cycle, stores refer specifically to water stores.

Fluxes/Flows

The movement of elements like carbon or water in various cycles which are essential for maintaining balance within the ecosystem. In the hydrological cycle, fluxes/flows refers specifically to the flow of water.

Residence time

The average time a particular molecule of water will remain in a specific body of water, calculated by volume divided by inflow or outflow rate.

Water store: Oceans

The largest water store, comprising 96.9% of the global water, with a residence time of 3,600 years.

Water store: Icecaps/Cryosphere

Comprising 1.9% of global water, mostly freshwater, with a residence time that can be up to 15,000 years depending on size.

Water store: Groundwater

Accounts for 1.1% of global water, with residence times from 100-200 years for shallow groundwater to up to 10,000 years for deep groundwater.

Water store: Rivers and lakes (surface water)

Comprises only 0.01% of global water.

Water store: Atmosphere

Represents 0.0001% of global water stores.

Flux: Land to Atmosphere

Annual water flux of 73km²/year.

Flux: Atmosphere to Ocean

Annual water flux of 373km²/year

Flux: Land to Ocean

Annual water flux of 40km²/year

Flux: Ocean to Atmosphere

Annual water flux of 413km²/year, representing significant evaporation.

Importance of fluxes/flows

The movement of water through the hydrological cycle is essential for maintaining balance within ecosystems.