The water cycle Flashcards
Outline the exothermic reactions occurring in the water cycle. (Energy lost to surroundings.)
1) Liquid to solid –> Freezing
2) Gas to solid –> Deposition
3) Gas to liquid –> Condensation
Outline the endothermic reactions occurring in the water cycle. (Energy gained.)
Solid to liquid –> Melting
Liquid to gas –> Evaporation
Solid to gas –> Sublimation
How much water is stored in the hydrosphere?
1.4 Sextillion litres
Of the 1.4 sextillion litres of water in the hydrosphere, what percentage is freshwater?
About 3% which most species need to survive.
Breakdown the distribution of earths freshwater.
69% is stored in the cryosphere
30% is groundwater in the lithosphere
0.3% is liquid freshwater in the earths surface (lakes and rivers.)
0.04% is stored as water vapour in the atmosphere.
What is the global hydrological cycle?
Water is continuously cycled between different stores globally, this is known as the global hydrological cycle.
This is a closed system where there are no inputs or outputs of water.
Outline a summary of the global hydrological cycle with inputs, outputs and stores.
The input in this cycle is only energy, this is solar energy from the sun.
The output is energy lost to space.
Some of the stores are as follows:
- Clouds, the atmosphere, liquid water, groundwater and lithosphere, the cryosphere.
Outline some key flows in the global hydrological cycle.
Clouds –> Liquid water sources and cryosphere through precipitation.
Liquid water to groundwater –> Infiltration. Back up through baseflow.
Liquid water –> Atmosphere through evaporation.
Water vapour to clouds –> condensation.
Water vapour to ice/cryo –> Deposition and vice versa with sublimation.
Ice to hydrosphere –> melting.
Why does the magnitude of the stores vary over time and space?
The amount of water cycled in a system varies from local (hillslope) to global. The magnitude of each store depends on the amount of water flowing between them.
Different flows occur at a range of spatial and temporal scales.
What is evaporation and how does the magnitude of this flow vary spatially and temporally.
Evaporation occurs when liquid water gains energy and changes state into a gas, becoming water vapour - the energy is typically gained from solar radiation. This increases the amount of water stored in the atmosphere as a gas.
The magnitude of the flow of evaporation varies by location and season. In places where there is a lot of solar radiation, a large supply of water and a large body of warm and dry air, the amount of evaporation will be high.
However in areas with less solar radiation, little liquid water and cool saturated air (can’t absorb much more water vapour,) this will be low.
What is condensation and how does the magnitude of its flows vary on spatial and temporal scales?
Condensation occurs when water vapour in the atmosphere undergoes an endothermic reaction and cools, becoming a liquid. It happens when air containing water vapour cools to it’s dew point (see below). This most commonly occurs when temps fall at night due to heat being lost to space.
Water droplets can stay in the atmosphere or flow to other subsytems eg can condense and form dew on vegetation. This decreases the volume of water stored in the atmosphere.
The magnitude of this flow depends on the amount of water vapour in the atmosphere and temp. Condensation will be highest when there is a large supply of water vapour in the atmosphere which coincides with a rapid drop in temperature.
What is a dew point?
The dew point is the temperature at which air becomes saturated with water vapor, causing condensation to form. In other words, it is the temperature at which the air can no longer hold all the moisture it contains and some of it must condense into liquid form. When the dew point temperature is equal to the air temperature, the relative humidity is 100% and dew, fog or frost may form.
What is cloud formation and precipitation and how does the magnitude of its flows vary on spatial and temporal scales?
Include cloud condensation nuclei and how cloud formation varies due to two main factors.
Precipitation is the main flow of water from the atmosphere to the ground, and occurs due to cloud formation.
Clouds form when warm air cools down, causing water vapour in the atmosphere to condense into water droplets which gather to form clouds. When these droplets get big enough, they fall as precipitation.
- Water droplets formed by condensation are too small to form clouds on their own, and require tiny particles of other substances (dust or soot) to act as cloud condensation nuclei. They give water a surface to condense on. This encourages clouds to form rather than allowing the moist air to disperse.
Cloud formation and precipitation can vary seasonally (more rain in winter than summer in the UK.) And by location (more precipitation in the tropics than the poles.)
Name three reasons for air to cool and subsequent clouds to form and precipitation to occur.
1) Other air masses - Warm air is less dense than cool air. Thus when the two meet the warm air is forced above the cool air and cools as it rises - this causes frontal precipitation.
2) Topography - When warm air meets mountains, it’s forced to rise and cools - Orographic precipitation.
3) Convection - When the sun heats the ground, ground moisture evaporates and rises up in a column of warm air. As it gets higher, it cools. This is convective precipitation.
Cryospheric processes; what are they>
Processes such as accumulation (freezing) and ablation (melting) can change the amount of water stored as ice in the cryosphere. The balance of accumulation and ablation varies with temperature.
