WC 2.1.4- precipitation and excess runoff Flashcards
what is the 1st type of precipitation (rainfall) and explain how it works
_________ ______ occurs when the sun’s energy heats the ______ of the Earth.
This causes water to _______ to form water vapour.
When the land heats up, it warms the air ______ it, making the air molecules move ________ apart.
Therefore making the air become lighter, so it _____ rapidly.
As the air rises, the water vapour in the air _______ into clouds and precipitates.
Convectional rainfall occurs when the sun’s energy heats the surface of the Earth.
This causes water to evaporate to form water vapour.
When the land heats up, it warms the air above it, making the air molecules move further apart.
Therefore making the air become lighter, so it rises rapidly.
As the air rises, the water vapour in the air, condenses into clouds and precipitates.
what is the 2nd type of precipitation (rainfall) and explain how it works
Frontal precipitation is when _____ air meets ____ air in a weather _____ (a boundary between two air masses). The molecules in the cold air are more ______ packed together, meaning it’s h_____ than the warm air.
The _____ air mass is forced over the ____ air.
As the warm air rises it is being c______, leading to the water _____ to condense to form clouds and then precipitates.
Frontal precipitation is when cold air meets warm air in a weather front (a boundary between two air masses). The molecules in the cold air are more densely packed together, meaning it’s heavier than the warm air.
The warm air mass is forced over the cold air.
as the warm air rises it is being cooled, leading to the water vapour to condense to form clouds and then precipitates
what is the 3rd type of precipitation (rainfall) and explain how it works
___________ _________ occurs when moist air is l______ as it moves over a _________ range.
As the air rises and cools, orographic clouds form.
Precipitation falls u______ of the _________ ridge.
Some falls abit downwind of the ridge which is called s_______.
On the rain s______ region rainfall is ___.
Heavy precipitation occurs up_____ of a prominent mountain range that is oriented ________ a pre______ wind from a w____ ocean.
Orographic Precipitation occurs when moist air is lifted as it moves over a mountain range.
As the air rises and cools, orographic clouds form.
Precipitation falls upwind of the mountain ridge.
Some falls abit downwind of the ridge which is called spillover.
On the rain shadow region rainfall is low.
Heavy precipitation occurs upwind of a prominent mountain range that is oriented across a prevailing wind from a warm ocean.
name the 2 Precipitation Formation Processes
- The Bergeron-Findeisen (ice-crystal) Process
- The collision process
name and explain the first precipitation formation process
The Bergeron Process
-occurs at high latitude in a high parts of a tall cloud called ‘cumulonimbus cloud’
-where temperature is below 0 degree C
- The vapour pressure is greater around droplets and lower around ice crystals
- water molecules move from water droplets to ice crystals
- this makes the ice crystal grow and the water droplets decrease in size
- ice crystal gets to a size and then falls as precipitation, but may melt as they fall
name and explain the 2nd precipitation formation process
The collision or coalescence process
- water droplets can be all different sizes
- the big droplets fall faster and then collide into the smaller droplets
- the droplets coalesce (stick together) to create a bigger droplet
- this falls quicker, makes it collide more frequently
- this is the accelerating growth process
what does runoff lead to an increase risk of?
risk of flooding
name the 6 (or 8) ‘Physical Causes’ of excess runoff
- Amount and type of rainfall
- Antecedent conditions
- Drainage density
- melting snow packs- a mass of lying snow that is compressed & hardened by it’s own weight
5.geology - relief (slope steepness)
- rock type
- vegetation
what are 2 (3) causes of excess runoff (flooding)
- Monsoons
WINTER monsoons
ITCZ is shifted south, air sinks so theres high pressure, so less rainfall as no clouds are made
SUMMER monsoons
-land heats up due to increased solar isolation
- air rises creates low pressure, so moist air is drawn in and convection and orthographic rainfall occurs as air rises over the Himalayas
= e.g. 90% of india’s rainfall occurs in a wet monsoon season - ITCZ
Inter tropical convergence zone
= a band of low pressure near the equator that is altered either north or south of equator depending on the season
- is responsible for wet and dry seasons in the topics
3 insolation
solar radiation received in the earths atmosphere
what are the 5 Human Causes of excess runoff
- urbanisation
- change in land use
- climate change
- deforestation-reduces interception
- River management (e.g. channel straightening- increases flow speed)
- floodplain drainage - if the soil is saturated or not
On a large timescale what is the most significant human cause that affects excess runoff
climate change - more intense and frequent storms
urbanisation- increased impermeable surfaces (e.g. more concrete)- faster surface runoff directly to the river
on a small timescale what is the most significant physical cause that affects excess run-off
The amount and type of rain
- due to how fast rain comes in a short amount of time- can causes flashy flood hydrographs
