4.1 Water systems

the main stores of the hydrological cycle are

oceans (96.5%), glaciers and ice caps (1.7%), groundwater (1.7%), surface freshwater (0.02%), atmosphere (0.001%), and organisms (0.0001%)

Hydrological cycle

includes transpiration, evaporation, sublimation, condensation, advection, precipitation, melting, freezing, surface runoff, infiltration, percolation, streamflow, and groundwater flow

Evaporation

water from storages, such as oceans, lakes and rivers, is transformed as it evaporates from liquid water to gaseous water vapour, Heat provided by the sun is required for evaporation of water

Transpiration

plants take up liquid water from the soil and release it as gaseous water vapour through their leaves. The combined water loss from evaporation and transpiration is known as evapotranspiration.Heat supports transpiration in plants

Advection

in the atmosphere, advection allows for the wind-blown movement of water vapour or condensed water droplets. The energy of the wind derives from solar radiation

Freezing/Melting

Solar radiation provides heat energy that causes solid snow or ice to melt into liquid water. In colder conditions, with less solar radiation and heat, water can freeze back into ice

Sublimation

If the air temperature is below freezing, sublimation of ice directly to water vapour can occur. The solid ice or snow absorbs so much heat energy that it is converted directly to gaseous water vapour

Condensation

As water vapour rises higher in the atmosphere, it cools and condenses into liquid water droplets, forming clouds. Heat is released as water condenses

Precipitation

The downward force of gravity allows liquid water to return to the Earth's surface as precipitation,  in the form of rain, snow, sleet or hail

Infiltration

Part of the water that falls on the surface enters the soil through infiltration,

Percolation

water movement in the soil

Runoff

The water not absorbed into the soil enters rivers, lakes or oceans as surface run-off. This process eventually restores streamflow

in rivers and lakes as well as groundwater flows

Human activities such as agriculture, deforestation, and urbanisation can alter these flows and storages

Can lead to reduced evapotranspiration and increased runoff, resulting in flash floods

Impacts of human activities

reduced vegetation cover, reduced interception, more ground compaction, more overland runoff, increased flooding, decreasing amounts of permeable surfaces

When a system is in steady state for a body of water

Total Input = Total Output