The Drainage Basin Is An Open System Within The Global Hydrological Cycle Flashcards
What is the only input into the system?
Precipitation
What is precipitation?
Any product of the condensation of atmospheric water vapour that falls under gravity
What are the three main types of precipitation?
Orographic
Frontal
convectional
What is orographic rainfall?
Rain that is produced from the lifting of moist air over a mountain
What is frontal rainfall?
It occurs when a warm front meets a cold front
The heavier cold air sinks to the ground and the warm air rises above it
The rising warm air cools
The cooler air condenses to form clouds
The clouds bring heavy rain
What is convectional rainfall?
When the suns energy (insolation) heats the earths surface and causes water to evaporate creating water vapour
The warm moist air then rises and cools and then condensates forming clouds
This leads to precipitation
What do all types of precipitation have in common?
Air being forced to rise
As the air rises it cools and cannot hold as much moisture as when it was warmer
What is a drainage basin?
An area of land drained by a river and its tributaries (river system)
Includes water in the water table and surface run-off
Is a drainage basin an open of closed system?
An open system as it has inputs, storage, transfers and outputs
What physical factors affect drainage basin input and flows and outputs ?
Slope gradient
Basin size (lag time)
Rock type ( permeable impermeable)
Rainfall type
Rainfall intensity
Basin shape
Drainage density
Vegetation type and cover
How do humans disrupt the local hydrological cycle?
Urbanisation
Deforestation
Afforestation
Water extraction
How does urbanisation affect the hydrological cycle?
Reduces infiltration and lag time
Impermeable surfaces
Increased discharge
How does deforestation affect the local hydrological cycle?
Reduces interception, evapotranspiration
Increased infiltration/ saturation
Increased surface run-off
High soil erosion (no root binding)
How does afforestation affect the local hydrological cycle?
Increasing interception and evapotranspiration
Reduce discharge in the drainage basin
Can take a long time for trees to mature
How does water extraction affect the local hydrological cycle?
Reduces discharge in the basin
How does basin size affect inputs/outputs and flows?
Influences lag time
Large drainage basin = increased lag time
Small basin = reduced lag time
How does basin shape affect inputs/ outputs/ flows?
Circular drainage basin means all points are equidistant so short lag time higher peak discharge
Elongated basin longer lag time and lower peak discharge as water has to drain from the furthest point of watershed
How does elevation and slope affect inputs/outputs/ flows?
Steeply sided valley means gravity assists water into channel = short lag time and high peak discharge
Gentle slopes have higher lag time and lower peak discharge
How does rock type affect inputs/outputs/ flows?
Permeable rock assists percolation so long lag time
Impermeable rock doesn’t allow drainage so high surface run-off short lag time
How does soil type affect inputs/outputs/flows?
Controls rate of infiltration, soil moisture, storage and rate of throughflow
Sandy soils have high infiltration rates so long lag time
Clay and silts have low infiltration so short lag time
How does drainage density affect inputs/outputs/flows?
Total length of streams in a drainage basin divided by basin area
Basin with impermeable rock/soil have high drainage density due to lack of infiltration/ percolation
Basin with permeable rock/soil have low drainage density
How does rainfall type affect inputs/outputs/flows?
Amount and duration determine ground saturation
Long periods of rain mean field capacity is met less infiltration more run-off = reduced lag time
What is field capacity ?
Saturation capacity the amount of moisture in the soil before it becomes saturated
How does rate of evapotranspiration affect inputs/outputs/flows?
Not constant all year round
High temp in summer increase rate reducing discharge
Low winter temps reduce evapotranspiration
What is cloud seeding?
When silver iodine pellets or ammonium nitrate act as condensation nuclei to attract water droplets aim is to increase rainfall
Where did the coverack flood happen?
Coverack Cornwall
South west England
When did the coverack flood happen?
July 18th 2017
What happened in coverack?
Flash flooding caused by intense rainfall over a short period
How much rainfall happened in coverack?
200mm in 3 hours
What caused the coverack flood?
Convectional rainfall
Temperatures were the 4th hottest summer since 1910
Temp in July was 33*c meaning convectional rainfall could occur
What is the ITCZ?
Inter tropical convergence zone
How does the ITCZ affect the hydrological cycle?
Seasonal shifts in the location of the ITCZ drastically affects rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer term changes in the ITCZ can result in severe droughts or flooding in nearby areas
