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the processes of the water cycle (the water balance (water balance…
the processes of the water cycle
the water balance
water balance equation summarises the flow of water in drainage basin over time
it states that: precipitation (P) = Evapotranspiration (E) + streamflow (Q) plus or minus (depending on whether water is entering or leaving storage) (S)
affects how much water is stored
Positive water balance happen in wer season
water deficit happens in dry season
Flows
transpiration
diffusion of water vap to the atmosphere from leaf spores of plants
responsible for 10% for of moisture in the atmosphere
influenced by:
temperature
wind speed
water availability
e.g. deciduous trees shed their leaves in climates with either dry or cold seasons to reduce moisture loss
condensation
Is the phase change of the vapour to liquid water
occurs when a cooled to its dew point
At this crucial temperature air becomes saturated with vapour resulting in condensation
clouds form through condensation in the atmosphere
condensation near or on the ground produces dew or fog
both types deposit large amounts of moisture on vegetation and other surfaces
precipitation
is water and ice that falls from the clouds
most common is, of course, rain and snow but also hail, sleet and drizzle
forms vapour in the atmosphere cools to its drew point and condenses into tiny water droplets to form clouds
in mountainous catchments, where snow often falls, it stays- means may be a considerable time lag between snowfall and run-off
intensity is the amount of of precipitation falling in a given time
High intensity precipitation moves rapidly overland into streams and rivers
Duration is the length of time that a precip event lasts
prolonged events may deposit exceptional amount of precip and cause flooding
In some parts of the world precip is concentrated in a rainy season
during the rainy season river discharge is high and flooding is common
In the dry season rivers may cease to flow altogether
clouds
Cumuliform clouds
flat bases and considerable vertical development
most often form when air is heated locally through contact with the Earth's surface
causes heated air parcels to rise freely through the atmosphere, expand (due to the fall in pressure with altitude) and cool
as cooling reaches the dew, condensation begins and clouds form
Stratiform
develop where an air mass moves horizontally across a cooler surface
this process is known as advection
cirrus
wispy
form at high altitude, consist of tiny ice crystals
they do not produce precipitation and therefore have little influence on the Water cycle
Clouds formation and lapse rates
clouds are visible aggregates of water or ice or both that float in the free air
cooling occurs when
Air warmed by contact with the ground or sea surface, rises freely through the atmosphere. As the air rises and pressure falls it cools by expansion
Air masses move horizontally across a relatively cooler surface- this is called advection
Air masses rise ad they cross a mountain barrier or as turbulence forces their ascent
A relatively warm air mass mixes with a cooler one
Lapse rates
three types of lapse rates
Envirornmental lapse rates (ELR)
The ELR is the vertical temp profile of the lower atmo at any given time. (on avg. the temp falls by 6.5 C for km of height gained
Dry adiabatic lapse rate (DALR
The DALR is the rate at which a parcel of dry air cools
Saturated adiabatic lapse rate (SALR)
The SALR is the rate at which saturate parcels of air cools as it rises through the atmo
describe the vertical distribution of temp in the lower atmosphere
as you get higher the temps get lower
how clouds from by convection
1) the ground heated by the sun warms the air in contact with the surface to 18C
2) because the air is warmer that its surroundings it is less dense and therefore buoyant
3) atmospheric instablity resluts in air raising freely in a convection current
4) when its internal temp reaches the dew point (8C) condensation occurs and clouds start to form
5) the air continues to rise so long as its internal temp is higher than surrounding atmo
6) above 4000m the atmo is is stable. air cannot rise freely in this zone becasue it is cooler then its surroundings
catchment hydrology
Evaporation
the phase change of liquid to vapour
the main pathway by which water enters the atmosphere
heat is needed to bring about evaporation (to break the molecular bonds)
the heat on the water released condensation into the atmo-
allows huge quantities of heat to be transferred around the planet
soil moisture is water that is held in spaces between soil participants
Utilisation
in warmer + drier seasons there is more output
Removes moisture from the soil
percolate