Watershed in the Pyrenees. Picture from the plane to Madrid by Mister P.
There are 2 scales at which we need to consider the Hydrological Cycle: the Global and the Drainage basin level.
The Global Cycle considers the movement of water between the TERRESTRIAL system, the OCEANS and the ATMOSPHERE.
The Drainage basin cycle relates to a particular catchment area. The image above shows a watershed (or divide). The ridge in the centre of the picture slopes away to left and right, and drainage networks or starting to develop which will transport any precipitation away to the left or right of the image.
PRECIPITATION: the transfer of water from the atmosphere to the ground surface in various forms: rain, snow, sleet, hail, fog drip, dew, frost,
EVAPORATION: Evaporation is the loss of moisture from the surface of the ground to the atmosphere as vapour, which requires the use of latent heat.
TRANSPIRATION: this is the loss of water from leaf surfaces of plants. The water is lost from the stomata, or openings which cover
EVAPOTRANSPIRATION:
POTENTIAL OR ACTUAL EVPT: EVPT is the abbreviation for Evapotranspiration, which is the loss of water as vapour from open water surfaces, soil surfaces and vegetation storage, plus depression storage.
The Potential evapotranspiration that could occur can be worked out using an equation. This relies on measuring temperature, and wind speed. One problem is that the measurements are often done from an open water surface.
INFILTRATION CAPACITY: Infiltration capacity suggests an amount of infiltration, but actually represents a rate (in millimetres per hour...) that water can penetrate into the soil through the interstices: pore spaces
Examples: (based on research)
The effect of grain size in initially wet soils without vegetation cover
Clays: 0-4mm/hr
Silts: 2-8 mm/hr
Sands: 3-12 mm/hr
