Topic 5: The Water Cycle And Water Insecurity Flashcards
(213 cards)
Why is the global hydrological cycle a closed system?
- because water cannot enter or leave the Earth and its atmosphere.
What are the three components of the cycle?
- flows
- stores
- processes
What are global stores?
- water stored as either water vapour, ice, saline or freshwater.
- examples of global stores of water include:
- oceans.
- lakes.
- aquifers (underground lakes).
- the cryosphere (glaciers and ice sheets).
What are local stores?
- Examples of local stores of water include:
- Vegetation storage.
- Surface storage.
- Soil moisture.
- Groundwater storage.
What are flows?
- Flows are how water moves from one store to another:
- Infiltration.
- Throughflow.
- Percolation.
- Stem flow.
- Base flow.
- Channel flow.
- Surface runoff.
What are processes?
- The following processes drive the flows between the stores:
- Precipitation.
- Evaporation.
- Transpiration.
- Cryosphere (glaciers and ice sheets) exchanges.
- Runoff.
What are the two processes that drive the global hydrological cycle?
- solar energy
- gravitational potential energy
What is solar energy?
- energy from the sun, heating water and causing evaporation/transpiration.
- more evaporation occurs as the global climate warms, increasing moisture levels in the atmosphere. This can lead to increased condensation as air cools snd therefore greater precipitation. This explains why some places experience increased cloud cover and precipitation as climate changes.
What is gravitational potential energy?
- ways in which water accelerates under gravity, thus transporting it to rivers and eventually to the sea.
- GPE keeps water moving through the system in a sequence of inputs, outputs, stores and flows.
What are global extremes?
- solar energy is concentrated in the Tropics, where much is absorbed by the sea. 74% of the world’s rainfall occurs at sea (most within the Tropics).
- different climatic regions vary in the nature and size of their inputs, transfers and flows of water. The polar and tropical rainforest regions provide clear examples of how different hydrological processes compare.
Polar hydrology:
- there are freeze/thaw seasonal differences.
- winter snow insulates the ground and 85% of solar radiation is reflected.
- permafrost creates impermeable surfaces.
- limited vegetation cover reduces heat absorption.
- the freeze-thaw cycle causes the seasonal release of biogenic gases into the atmosphere, as well as carbon and nutrients into rivers and seas.
- annual precipitation is less than 200 mm.
- it is characterised by orographic or frontal precipitation.
Example of polar hydrology:
- the cryosphere: here, seasonal thaws bring increases surface saturation and thinning permafrost. If this thaw becomes continuous, water flows away abc is lost through the prices known as cryosphere loss.
Tropical rainforest hydrology:
- few seasonal differences.
- dense vegetation intercepts and consumes up to 75% of precipitation.
- 50-75% of precipitation then returns by evapotranspiration.
- rainforests generate their own rain; most is recycled within the Tropics.
- there is limited surface infiltration or groundwater.
- there are constant high temperatures.
- it is characterised by conventional rainfall and high humidity.
- annual precipitation is above 2000 mm
Example of tropical rainforest hydrology:
- tropical rainforests: here, permanently dense forest produces high rates of evapotranspiration, with water returning to the surface as precipitation that feeds large rivers such as the Amazon.
What is the global water budget?
-
Why are the Tropics important?
-
Why are the polar regions important?
- the polar regions contribute to the circulation of water and the transfer of heat around the world, which drive the global hydrological cycle.
How does the thermohaline circulation work?
1) ocean water in the polar regions is colder, more saline and denser than in the Tropics, so it sinks.
2) the cold sinking water draws in warmer water from the ocean surface above, which in turn draws water across the surface from the Tropics.
3) rhe movement of water from the Tropics draws colder water up from the ocean bottom, to be warmed again
Fossil water …
…
How do drainage basins lose water?
- evaporation and evapotranspiration to the atmosphere
- surface runoff to the sea
- percolation into groundwater stores
Pathways water follows after precipitation?
- reach the land surface and then infiltrate the topsoil.
- run off the surface as overland flow
- be evaporated back into the atmosphere.
Why may pathways be delayed?
- the water could be intercepted by plants or buildings, before either evaporating or infiltrating into the surface.
- some surface water infiltrates through the surface and eventually percolates through the rocks underneath to become groundwater, where it may be stored in aquifers for some time.
The hydrological cycle - inputs
- precipitation
Precipitation definition:
- moisture in any form