describe orographic rainfall
- air is forced to rise over a barrier such as a mountain
- due to cooler temperatures (resulting from higher altitudes) the water vapour condenses into clouds
- heavy rain on the highlands, which empties the clouds and leaves a rain shadow down the slope
describe cyclonic (frontal) rainfall
- warm and cold air move towards each other
- as warmer air is less dense it rises over the colder denser air
- as it rises it cools and condenses, the extra potential energy also means it looses the ability to store the vapour so it precipitates
describe convectional rainfall
- warm air rises vertically up over cool air
- warm air cools due to increased altitude and condenses
- as more vapour builds up, it rains
- as the air cools down it begins to descend and is replaced by warmer air
what conditions are needed for rainfall
- air cooled to saturation point with relative humidity near 100%
- condensation nuclei, such as dust particles to facilitate the growth of droplets in clouds
- temperature below the “dew point”, temperature at which dew forms, a measure of atmospheric moisture
which water store has the longest residence time
crysphere- 15,000 years
what is the largest store of water and what is its percentage. What is its residence time ?
Oceans, 96.9%
residence time: 3600 years
what impacts the drainage basin hydroglogical system
1) the volime of percipitation direct impact on discharge, the higher the amoun the lower the variability
2) Type of percipitation (rain, snow or hail) snow can act as a temporary store and large fluxes of water can be released after a thaw, resulting in rapid melting
3) seasonality- some climates such as the mediteranean, a monsoon or continued have strong seasonal patters of percipiration which have major impact on the physical processes operating in the drainage basin system
4) percipiration intensity - If percipitation of e.g. rain is intense then it is less likely that it will infiltrate the soil as it will be laready saturated
5) variability:
- secular variability, long term for example as a resilt of climae change
- periodic variability, happens in an annual seasonal monthly diuralcontext
- stochaic variability, results from random factors, for example the localisation of a thunder storm within a basin
6) distribution of percipitation form basin (mainly for large basins e.g. nile) were bateries start in different climatic zones. At a local scale and shorter time scales,the location of a thunerstorm can have a large impact temporarily as inputs will vary
list which land types intercept most, starting from most interception to least
- coniferous
- decidious, summer + spring
- decidious, autumn + winter
- arable farmland
- deforested
what atmospheric factors contribute to high levels of intercpetion
- intermitent percipiration
- sunlight
- not windy conditions
what increases infiltration rates
- many trees with many roots
- porous and sandy soil
- low water table
- porous/permeable rocks
what increases surface run-off
- soil saturation
- imperbeable rocks
- clay rather than sany soil
- urbanisation
- steeper slopes
wjat increases rates of soil throughflow
- sandy soil
- saturated soil
- premiale rock
define evapotransipration
total amount of moisture removed from drainage basin by process of evaporation and transpiration
what factors affect evapotranspiration and how do they affect it
- temperature: icreases rate of evaporation, evaporation and temperature increases with sunshine hours
wind: will increase the rate of evaporation by reducing the relative humidity - vegitation cover: transpiration increases proportionally with vegitaiton cover which depends on the season and type of vegitation. Low albedo vegitation, such as a dark forest will absorb more solar radiation which increase transpiration
- soil moisture content: determines the volume of water available for transpiration. It is dependandt on soil and rock permeability
define Channel flow
water that has collected to flow in a rivulet, stream or river and is another output from the drainage basin system
define discharcharge
- discharge of a river is the volume of water passing a specific gorging station per unit time and is measured in cubic metres per seceond, cumecs
- It is dependant on: percipitation flowing in the channel, contributions from drainage basin stores via surface run off, throughflow or groundwater flow
what are the human disruptions in the drainage basin
cloud seeding dam construction urbanisation ground water extraction arable and pastoral farming
what is cloud seeding
expulsion of particulates from power stations such as hydrosopic nuclei which provide space for water milecules to attatch onto to form clouds
how does dam construction intefere with drainage basin
- increase surface storage
- exposed water increases evaporation
how do aaquifiers interfere with drainage basin
- water is taken from ground
- goundwater stores decrease
- lowers the groundwater flow
