2.1.4 - precipitation and excess runoff in the hydrological cycle

What is excess runoff

When there is more water on the surface than usual

What does water require in order to make the transfer from vapour to liquid

A non-gaseous surface

What does condensation take place around

A small piece of dust or sea salt particles this is called a condensation nuclei

Why is warm air less dense than cold air

Because as the particles heat up they vibrate more and expand - moving away from eachother - and then because there is less space between the particles it is less dense

Why does hot air float upwards

Because it is less dense than the surrounding matter the hot air moves up and around the cold air - this is called air uplift

Frontal rainfall diagram

During frontal rainfall where is rain heavier

At the cold front

What is this also known as

A depression - when it’s raining

What are the 3 types of rainfall

• convectional

• Frontal

• Orographic

Which is the most common type of rainfall

Frontal

Frontal rainfall

• warm air is forced to rise above the cold air

• It cools when it reaches high altitude and condensation occurs

• When the water droplets become too heavy in the cloud they fall due to gravity

Orographic rainfall

• warm air from the coast blows inland from the west in the uk

• When the warm air comes into contact with the hills e.g. Pennines it is forced over them into the cooler air above

• The warm air meeting the cold air creates condensation around a condensation nuclei

• This then forms a cloud and will eventually read to precipitation when the clouds are too heavy so the water will fall due to gravity

Convectional rainfall

• water on the surface is heated due to the solar radiation from the sun

• Warm air rises above the cool air

• This causes condensation around a condensation nuclei

• Rain may then occur if the clouds become too heavy

What are the 2 main theories of precipitation formation

• the collision coalescence

• The Bergeron-findeisen process

The collision coalescence

• supersized condensation nuclei e.g. large sea salt particles provide seeds around which very larger water droplets form

• The larger super droplets fall under the force of gravity and collide with smaller droplets, absorbing them

The Bergeron findeisen process

• clouds at high altitudes contain a mixture of water droplets and ice crystals

• The ice crystals absorb water droplets, causing them to grow

• The ice crystals are fractured as they are jostled by Hugh altitude air currents

• This movement causes hexagonal ice shapes to develop with a larger surface area

• Now more water vapour can condense around the ice, making them grow faster

• When the ice crystals become too heavy they fall and if the air they fall into is warm enough then they melt

What are similarities between the CCP and the BFP

• both influenced by gravity

• Both increase in size

• Both absorb water vapour

• Both need condensation nuclei to form

What are some differences between the CCP and the BFP

• BFP is ice crystals and water vapour where as CCP is just water vapour

• In CCP the particles have to be moving to absorb water vapour

• CCP isn’t influence by high altitude currents

• CCP has pear/circle shape where as BFP has a hexagonal shape

What are the physical factors that affect excess runoff

• snowmelt/ablation

• Storm activity

• Monsoon season

What human factors affect excess runoff

• urbanisation

• Drain and sewer network

• Deforested areas

Physical factors more likely to cause excess runoff

• possibly as they occur naturally and so are more difficult to manage however things like urbanisation can’t be managed and we can’t pull down a full city as we have already built it

How many people died in Sierra Leone due to the mudslide

1141 people

Why was Sierra Leone more succeptible to a mudslide

Deforestation had weekend the soil as there wasn’t any roots holding it together

How does deforestation change the water cycle

• increase in surface storage and overland flow

• Soil is compacted by rain drop impact

• Water can’t soak into the ground