ZIMSEC O Level Geography Notes: The hydrological cycle.
Water does not leave or enter the planet earth.
It is instead continuously transferred between the atmosphere and the oceans.
The system of inputs, storages,flows and outputs is known as the water or hydrological cycle.
Inputs – refers to water coming into the system.
Precipitation– refers to all forms of moisture that reach the Earth’s surface e.g. rain, snow, sleet and hail.
Interception – this is when precipitation lands on buildings, vegetation and concrete before it reaches the soil.
Interception storage is only temporary as it is often quickly evaporated.
Vegetation storage – this is water taken up by vegetation. It is all the moisture in vegetation at any one time.
Surface storage – the total volume of water held on the Earth’s surface in lakes, ponds and puddles.
Groundwater storage – the storage of water underground in permeable rock strata.
Channel storage -the water held in a river or stream channel.
Flows and Processes – water moving from one place to another.
Baseflow – water that reaches the channel largely through slow throughflow and from permeable rock below the water table.
Channel flow – the movement of water within the river channel. This is also called a river’s discharge.
Groundwater flow – the deeper movement of water through underlying permeable rock strata below the water table. Limestone is highly permeable with lots of joints and can lead to faster groundwater flow.
Infiltration – the downward movement of water into the soil surface.
Interflow – water flowing downhill through permeable rock above the water table.
Percolation – the gravity flow of water within soil.
Stemflow – water running down a plant stem or tree trunk.
Surface Runoff – the movement of water over the surface of the land, usually when the ground is saturated or frozen or when precipitation is too intense from infiltration to occur.
Throughflow– the movement of water downslope within the soil layer. Throughflow is fast through pipes (cracks int he soil or animal burrows).
Outputs – water leaving the system.
Evaporation – the transformation of water droplets into water vapour by heating.
Evapotranspiration – the loss of water from a drainage basin into the atmosphere from the leaves of plants plus loss from evaporation.
Transpiration – evaporation from plant leaves.
River discharge – the amount of water that passes a given point, in a given amount of time.