5.2

Question 1

When does orographic rainfall occur

Answer 1

Orographic rainfall occurs when air is forced to rise over a barrier e.g mountain , causing it to cool and condense forming clouds and rain. When the air is rising lots of rainfall is distributed onto the immediate area however as the rising air descends not much rain is distributed. This is known as the rain shadow affect

Question 2

When does cyclonic rainfall occur

Answer 2

Cyclonic rainfall occurs when warmer,less dense , lighter air is forced to rise above colder, denser air. As it rises the warmer air cools and its ability to hold water vapour decreases. It then condenses and clouds and rain forms

Question 3

When is interception is worse

Answer 3

Interception is worse when there is lots of rainfall for a long duration of time as he branches are highly saturated so more excess water falls away

Question 4

When is interception greatest

Answer 4

Interception is greatest when there is rainfall for a short duration as dry branches have the greatest water storage ability

Question 5

When does convectional rainfall occur

Answer 5

Convectional rainfall occurs when land rises in temperature causing the air above it to become hot, rise and expand. As it rises the airs ability to hold water vapour decreases and condensation occurs. If it then continues to rise rain will fall

Question 6

Which type of trees allow for greater interception

Answer 6

Dense coniferous needles allow for greater accumulation of water compared with deciduous trees which allow for less interception. This is shown by evidence as coniferous forests e.g the Qillian mountain conifer forest intercept 25-35 % of annual rainfall whereas deciduos forests only intercept 15-25 % of annual rainfall. This contrast is partly to do with the fact that deciduous trees shed their leaves but coniferous trees do not shed their needles

Question 7

Which crop type allows for greater interception

Answer 7

Denser coniferous crops allow for greater interceotion than sparser deciduous crops

Question 8

What wind conditions allow for greatest interception

Answer 8

Low wind conditions minimise the amount of interception dislodged from the vegetation and reduce evaporation rates. Whereas high winds maximise interception dislodgement and increase evapotranspiration rates

Question 9

What conditions will allow for high infiltration

Answer 9

Precipitation-For infiltration to be at its highest there needs to be moderate antecedent rainfall to ensure soil permeability so the soil is not too dry or too saturated

Gradient-for infiltration to be at its highest the ground needs to have a shallow gradient as too steep gradient makes water run off the surface

Soil depth and type- for high infiltration there needs to be Sandy soils with uncompacted surfaces and a high depth as the precipitation can flow through and around the small particles

Vegetation-To allow for maximum infiltration there needs to be high forest density or moorland with low seasonal variation to maximise interception

Question 10

What conditions will allow for low infiltration

Answer 10

Precipitation-Lots of precipitation will cause the ground to become saturated and less infiltration to occur. Also if there has been lots of rainfall previously then the ground is more likely to be saturated and less infiltration can occur.

Gradient-very steep slopes encourage overland run off ( surface run off)

Vegetation-permenant pasture on land decreases infiltration rates significantly as it compacts the soil and allows for less infiltration

Question 11

What is evapotranspiration

Answer 11

Evapotranspiration is the amount of water in moisture removed from a drainage basin by process of evaporation and transpiration

It is an output from the drainage basin open system

Question 12

What is evaporation

Answer 12

Evaporation is the process by which liquid water is transformed into gaseous water vapour

Question 13

What is transpiration

Answer 13

Transpiration is the biological process by which water is drawn upwards from the soil by plants and evaporated through stomata in the leaves

Question 14

What is potential evapotranspiration

Answer 14

Potential evapotranspiration is the amount of evapotranspiration that could take place given unlimited supplies of water in the environment

Question 15

What is channel flow (discharge)

Answer 15

Channel flow is water that has collected to flow in a water flow system (e.g a rivulet, stream or river)

It is an output from the drainage basin open system

The discharge of a river is the volume of water passing a specific point per unit of time

Discharge is dependent on precipitation amount and contributions of water from drainage basin stores (surface run off, through flow or groundwater flow )

Question 16

What are factors affecting the rate of evapotranspiration

Answer 16

Temperature - rate of evaporation increases with temperature

Wind - wind increases rate of evaporation by reducing relative humidity and preventing air saturation

Vegetation cover - transpiration rate increases with high vegetation density and vegetation. Vegetation with a low albedo affect will absorb solar radiation, increasing evaporation

Question 17

What is saturated over land flow

Answer 17

Saturated over land flow is when water accumulates in the soil until the water table reaches the surface , forcing further rainwater to run off the surface

-This is common where there are thin soils of moderate permeability especially in high moisture concavities near streams or river banks

Question 18

What is infiltration excess overland flow

Answer 18

Infiltration excess overland flow is when rainfall intensity exceeds the infiltration capacity. When this happens excess water flows over the ground surface and is quickly delivered to river channels. This however increases the risk of downstream flash flooding

Question 19

What is soil through flow

Answer 19

Soil through flow is the internal transfer of water downslope through soil via natural pipes and percolines ( lines of concentrated water flow between soil horizons to the river channel )

Question 20

What is groundwater flow

Answer 20

This is the slow transfer of water ( percolated) through previous ( joints and bedding planes) and porous ( pore spaces) rocks

-It is a vital regulatory component in maintaining a steady level of channel flow in varying conditions

Question 21

What is percolation

Answer 21

Percolation is the continuation of infiltration deeper below ground

• It is the deep transfer of water into permeable rocks ( pervious e.g Carboniferous limestone or porous e.g. chalk and stand stone)
• Percolated water reaches a saturated zone ( water table ) above impermeable rock and creates groundwater storage and aquifers

Question 22

What is cloud seeding

Answer 22

Cloud seeding is an attempt to try and change the amount of type of precipitation by dispersing substances ( silver iodide pellets or ammonium nitrate) into the air to serve as cloud condensation nuclei ( hygroscopic nuclei). It is improving with new technology and is used in drought stricken countries to increase rainfall.

-It is an input disruption to the drainage basin

Question 23

What is a case study for somewhere where cloud seeding has been used

Answer 23

• China used cloud seeding in Beijing just before the olympics in 2008 in order to create rain to clear the air of pollution
• The USA used it during the Vietnam war in order to draw out the monsoon season and create difficult, muddy conditions for opposition fighters
• It was also used in Texas in 2015 to reduce the impact of drought

Question 24

How does urbanisation disrupt the drainage basin

Answer 24

Urbanisation creates impermeable surfaces that reduce infiltration and increase surface runoff and through flow through artificial drains ; streams and river discharges often increase rapidly as a result
Case study: across the UK, urbanisation has increased flood risk in many towns and cities such as Winchester and Maidenhead ( 2014 floods) and Manchester ( 2015 floods)

Question 25

How does deforestation affect the drainage basin system

Answer 25

Deforestation leads to a reduction in evapotranspiration and an increase in surface run off. This increases flooding potential , leads to a decline in surface storage and a decrease in lag time between peak rainfall and discharge

-research on deforestation in Nepal shows a range of negative impacts linked to deforestation including an increase in sediment load downstream

Question 26

How does afforestation affect drainage basin system

Answer 26

Afforestation should In theory have the opposite impact to deforestation however recent research has shown in the river Severn in mid wales that there is a period of time of 30 years after the planting of young trees where there is an increase in run off and sediment loss as a result of compaction of the soil by tractors and planting equipment

Question 27

How does land use affect drainage basin system

Answer 27

Infiltration is up to 5 times greater under forests compared to grassland. This means when land is initially converted to farmland from forest there is reduced interception, increased soil compaction and more overland flow .

-If farmland is used for pastoral uses e.g grazing cows then the trampling of animals leads to soil compaction and less infiltration. If farmland is utilised for arable uses e.g for ploughing for crop farming increases infiltration by loosening and aerating soil

Question 28

What affect does irrigation have on groundwater levels

Answer 28

Human use of irrigation for extensive farming has led to declining water tables and a lack of water in areas such as Texan aquifers.

Question 29

What is a case study example of the negative affects of irrigation

Answer 29

The Aral Sea ( between Kazakhstan and Uzbekistan) is an example of the damaging affects of over extraction of water. In the 1960s soviets over used water from the syr darya and Amu Dayra for irrigation of cotton farms which greatly reduced the amount of water reaching the Aral Sea. By 1994 water levels had fallen by 16m , the surface area declined by 50m , the volume by 75 percent but salinity levels increase by 300% with major ecological projects

Question 30

What affect did the industrial decline have on groundwater levels

Answer 30

In UK cities e,g London industrial decline has led to less groundwater being extracted for manufacturing activities. This has led to the opposite problems as groundwater levels have began to rise. There has been surface water flooding , flooding of cellars and increased leakage into tunnels e.g London Underground

Question 31

Where can we see the affects of deforestation on the global hydrological cycle

Answer 31

We can see the affects of deforestation on the global hydrological cycle in the Amazonia.

• Over twenty per cent of the forest has been destroyed at an accelerating rate in the last 50 years
• This has had a great affect on the hydrological cycle as in a forest environment 75 percent of intercepted water is returned by EVT to the atmosphere, which reduces to around 25 percent when the forest is cleared. This leads to a drier climate which leads to desiccation and further rainforest degradation
• Amazon deforestation can also affect the water cycle in other ways. More water runs off into the Amazon drainage system ( due to the lack of interception)
• This increase in run off exacerbates the possibility of severe flooding and mudslides. It also leads to aquifer depletion as less water infiltrates to recharge them
• the increase in run off also increases soil erosion

Question 32

What are factors affecting the inputs to the drainage basin ( precipitation)

Answer 32

Seasonality-In some climates (monsoon +Mediterranean) there are strong seasonal patterns of rainfall. Therefore time of year determines precipitation input within the drainage basin

• Variability-sudden or long term changes to the climate can happen, which would affect precipitation levels and so the drainage basin as a whole. ( secular variability which is long term climate changes , periodic variability which is annual / seasonal changes to climate , stochastic variability which is random factors leading to changes in the climate leg localisation of thunderstorm )
• Latitude has major impact on climate and so amount and type of precipition . In general , the higher the latitude from the equator, the colder the climate , so there is more snow than rain