Deck 32- Inputs, flows, stores, outputs

Question 1

What 3 conditions are required for precipitation to form?

Answer 1

1) Air cooled to saturation point with a relative humidity of 100%

2) Condensation nuclei such as dust particles to facilitate the growth of droplets in clouds

3) A temperature below dew point (the temperature at which dew forms, it is a measure of atmospheric moisture)

Question 2

How does cyclonic precipitation form?

Answer 2

Occurs when two masses of different temperatures meet. The warmer air rises, it then cools and expands in the upper atmosphere. Condensation then occurs leading to the formation of clouds then precipitation.

Question 3

What characteristics does cyclonic precipitation have?

Answer 3

Heavy and prolonged rainfall. It usually brings grey, overcast skies and rain for the most of the day. It is the most common type of precipitation in Newcastle.

Question 4

How does convectional precipitation form?

Answer 4

The sun heats the Earth’s surface and the air immediately above it. The heated air then rises and expands. It then cools and condensation occurs forming cumulus clouds. This then leads to intense precipitation which continues if more air is heated and then rises. Eventually the cooler air descends and replaces the warm air.

Question 5

Where is convectional precipitation mostly likely to occur?

Answer 5

Warm tropical climates. It is becoming more common in South England in summer months.

Question 6

How does orographic (relief) precipitation form?

Answer 6

Occurs when a moist air mass moves towards an area of high relief i.e. mountains. The air is forced to rise over the mountains where it cools and condenses leading to increased precipitation. On the other side (the lee side) of the mountain the air sinks and warms leading to a drier climate (known as the rain shadow effect).

Question 7

Which areas of the UK experience high levels of orographic precipitation?

Answer 7

Mountainous regions such as the Scottish Highlands, Lake District, Peak District and Snowdonia

Question 8

How does type of vegetation impact of rates of interception?

Answer 8

Deciduous woodlands have more broadleaf trees which will intercept higher amounts of rainfall.

However, coniferous woodlands have densely packed pine leaves throughout the year so are more effective at holding precipitation during the winter (particularly snow).

Question 9

How does seasons in the UK impact rates of interception?

Answer 9

Summer = higher due to more leaves on trees

Winter = less as less leaves on trees

Question 10

How does the intensity and duration of a precipitation event impact on the rate of interception?

Answer 10

More intense and longer precipitation events means that the precipitation is more likely to reach the ground via throughfall as the leaves may break.

Question 11

What is infiltration capacity?

Answer 11

Infiltration capacity is the maximum rate at which rain can be absorbed by a soil in a ‘given condition’ and is expressed in mm/hr.

Question 12

How does soil texture impact on infiltration rate?

Answer 12

Sandy soils = higher infiltration rate due to larger and more frequent pore spaces

Clay soils = very low rates of infiltration due to impermeable texture

Question 13

How does slope angle impact on infiltration rate?

Answer 13

Steep slopes = lower infiltration rate as water flows on the surface due to the influence of gravity

Question 14

How does the duration of a rainfall event impact on infiltration rate?

Answer 14

At the start of the rainfall event infiltration rates are high. As the rainfall event continues the rate decreases as infiltration capacity is reached.

Question 15

What is antecedent moisture and how does it impact on infiltration rate?

Answer 15

Antecedent moisture refers to the level of moisture in the soil due to prior weather conditions. Areas that have experienced high levels of precipitation in the prior weeks to a new rainfall event will have lower infiltration rates as they are closer to infiltration capacity.

Question 16

How does % vegetation cover impact on infiltration rate?

Answer 16

Bare earth initially has high rates of infiltration and capacity is reached, quickly leading to less infiltration over time. Forests initial infiltration low as water is intercepted, this increases when interception stores have been filled.

Question 17

How does bedrock lithology impact on rates of percolation?

Answer 17

Impermeable bedrock such as igneous (granite) and metamorphic (slate) rocks do not allow water to percolate into groundwater stores.

Permeable bedrock such as sedimentary (sandstone) rocks allow water to percolate into groundwater stores.

Question 18

Why does impermeable bedrock result in an increased flood risk?

Answer 18

Little to no percolation occurs resulting in a build up of water in surface stores increasing flood risk.

Question 19

What is overland flow and how fast is it?

Answer 19

Overland flow occurs when water flows on the surface towards a river channel. It occurs when precipitation intensity is greater than the infiltration capacity and allows for rapid flow of water into the channel.

Question 20

What is throughflow and how quickly does it occur?

Answer 20

Throughflow is the lateral transfer of water through soils. It is slower than overland flow but depending on soil texture can occur quite rapidly (i.e. sandy, porous soils).

Question 21

What is groundwater flow and how quickly does it occur?

Answer 21

Groundwater flow occurs when water travels through the rock layer to reach the river channel. Tt can take a very long time for water to travel through permeable or porous rocks. This means that groundwater flow provides a steady input of water into the channel in varying weather conditions.

Question 22

What are the three outputs from a drainage basin?

Answer 22

-River mouth
-Evaporation*
-Transpiration*

*The combined contribution if known as evapotranspiration