Processes of the water cycle

Water balance equation

Precipitation (P) = Evapotranspiration (E) + Streamflow (Q) +/- Storage

Flows (role is to link the stores): precipitation, evaporation, transpiration, run-off, infiltration, percolation and throughflow (7)

Precipitation: Forms when vapour in the atmosphere reaches its dew point and so condenses into small water droplets or ice particles to form clouds.

These droplets or ice particles aggregate, reach a critical size and then leave the cloud as precipitation

Precipitation varies in character -

Whilst run-off from rainfall may be rapid, precipitation falling as snow fall may mean there's a considerable lag between snowfall and run-off

Intensity: high-density precipitation moves rapidly because it falls at a capacity that exceeds the soil's infiltration capacity

Duration: prolonged events may cause the oversaturation of soils, overland flow and potential flooding

When precipitation is concentrated seasonally, like in the Mediterranean, there are high levels of river discharge that can often lead to flooding and during periods of low precipitation, rivers may cease altogether

Transpiration: diffusion of water vapour into the atmosphere through the leaf pores of plants

Influenced by the temperature and wind speed and water availability in plants

Condensation: cloud formation

Types of clouds

Cumuliform

Stratiform

Cirrus

Formation of clouds: cooling of the air to condense occurs when

Warm air rises and as it moves through the atmosphere, the pressure falls and the air cools by expansion (adiabatic expansion)

Air masses move horizontally across a cooler surface (advection)

Air masses rise as they cross a mountain barrier

Warm air mixes with cooler air

Lapse rates: vertical distribution of temperature in the lower atmosphere and the subsequent temperature changes occurring within an air parcel

Environmental lapse rate (ELR): Vertical temperature profile of lower atmosphere. Temp. falls by 6.5 degrees Celsius/km

Dry adiabatic lapse rate (DALR): rate at which parcel of dry air cools. 10 degrees Celsius/km.

Saturated adiabatic lapse rate (SALR): Rate at which a saturated parcel of air cools. 7 degrees celsius/km.

Catchment hydrology

Evaporation

Infiltration, groundwater flow, run off, throughflow

Interception

Cryospheric processes