5.1 the importance of the global hydrological cycle

Question 1

Is the hydrological system open or closed?

Answer 1

closed

Question 2

What drives the hydrological system?

Answer 2

solar energy and gravitational potential

Question 3

How important is the hydrological system to life on earth?

Answer 3

enormous importance

Question 4

Why is the hydrological system a closed system?

Answer 4

The total amount of water in the world doesn’t change. No inputs occur and nothing is lost. However, water’s form changes all the time: in areas that are warming, ground surfaces dry out as evaporation increases. Global air circulation then takes this extra vapor to cooler areas, where it condenses into clouds and precipitation

Question 5

How is climate change affecting residence time and fluxes

Answer 5

More evaporation occurs as the global climate warms, which increases moisture level in the atmosphere. This in turn can lead to condensation as air cools and therefore greater precipitation. This explains why some places may experience increased cloud cover/ precipitation as climate changes. Shifts in the world’s climatic zones mean that some stores are depleting

Question 6

How much water is in the Earth atmosphere system? How much is accessible to humans?

Answer 6

97% of water is in oceans and is too salty for humans to consume. A further 2% is locked in the cryosphere and so only 1% is available to us for drinking and only 0.4% is contained in surface lakes, rivers, the biosphere and atmosphere at any one time. This water is transferred globally in fluxes

Question 7

Where might fossil water be found?

Answer 7

This exists in polar regions and beneath many deserts. New technologies now make it possible to access water stores known as aquifers beneath Greenland’s icesheet or Kenya’s desert. Kenya’s Lolikipi aquifer contains 200 billion cubic metres of freshwater, which is enough to supply Kenya for 70 years

Question 8

What are fluxes?

Answer 8

the rate of flow between stores

Question 9

What is the cryospehere?

Answer 9

areas of the earth where water is frozen into snow or ice

Question 10

What is the global water budget?

Answer 10

the annual balance of water flows and size of stores.
Oceans lose more water through evaporation than they gain through precipitation, whereas the opposite is true for landmasses. Surface runoff makes up the difference- known as balance. If this balance were disturbed, the oceans would receive more water and the continents would dry up. This balance is known as the global water budget and it ensures this doesn’t happen.

Question 11

What is residence time?

Answer 11

the average time a water molecule will spend in a reservoir or store

Question 12

What is fossil water?

Answer 12

ancient, deep groundwater from former pluvial periods

Question 13

What is an aquifer?

Answer 13

a permeable or porous rock which stores water

Question 14

What is blue water?

Answer 14

Water stored in rivers, streams and groundwater in liquid form (visible part of the hydrological cycle)

Question 15

What is green water?

Answer 15

water stored in the soil and vegetation (the invisible part of the water cycle)

Question 16

Where is solar energy concentrated?

Answer 16

in the Tropics, where much of the energy is absorbed by the sea

Question 17

What percentage of rainfall happens at sea?

Answer 17

74% - most within the tropics

Question 18

What is the polar hydrological cycle like (cryosphere)?

Answer 18

-there are freeze/thaw seasonal differences
-winter snow insulates the ground and 85% of solar radiation is reflected
-permafrost creates impermeable surfaces
-lakes and rivers are frozen
-limited vegetation cover reduces heat absorption
-the spring thaw causes rapid runoff
-summer thaw produces surface run-off, increasing evaporation
-the freeze-thaw cycle causes the seasonal release of biogenic gases
-It’s characterized by orographic or frontal precipitation and low humidity
-annual precipitation is less than 200mm

Question 19

What is cryosphere loss?

Answer 19

In the cryosphere, seasonal thaws bring increased surface saturation and thinning permafrost. If this thaw becomes continuous, water flows away and is lost

Question 20

What is the hydrological cycle like in the tropical rainforest?

Answer 20

-few seasonal differences
-dense vegetation intercepts and consumes up to 75% of precipitation
-50-75% then returns by evapotranspiration
-Evapotranspiration cools the air as energy is used in the process
-rainforests generate their own rain - ‘cloud factories’
-less than 25% of rainfall reaches rivers
-limited surface infiltration and groundwater
-constant high temperatures
-Convectional rainfall and high humidity
-annual precipitation is over 2000mm

Question 21

Why does water not stay in the atmosphere for long?

Answer 21

Its residence time is short because the yearly flux of 460,000km cubed is almost 35 times greater than the amount of water the atmosphere can hold at any one time

Question 22

What is the importance of the tropics in the hydrological system?

Answer 22

The steep angle of the sun over tropical oceans allows intense solar radiation, causing high evaporation. Trade winds transfer water vapor towards the inter-tropical convergence zone. There, strong convectional currents lift the air so that it cools and condenses into clouds, causing heavy rainstorms. Most of the world’s rainfall is created in the ITCZ, so this is the biggest flux transferring water from ocean to land. The huge atmospheric flows of moisture are called tropospheric rivers.

Question 23

What is the importance of polar regions in the hydrological system?

Answer 23

the cryosphere holds around 2/3rds of the world’s freshwater. Therefore as some of the water begins to melt, the polar regions contribute to the circulation of water and transfer of heat around the world. An ocean circulation occurs, known as the thermohaline circulation- sometimes also known as the global conveyor belt

Question 24

How does the thermohaline circulation work?

Answer 24

1. ocean water in the polar region is colder, more saline (salty) and denser than 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 across from the tropics
3. The movement of water from the tropics draws cold water up from the ocean bottom, to be warmed again

Question 25

What is the order of importance (size) of the main water stores?

Answer 25

-Oceans (liquid - 97%)
-Cryosphere (solid - 1.9%)
-Terrestrial surface groundwater (blue and green water - 1.12%)
-Atmosphere (vapour - 0.001%)

Question 26

How does residence time vary between the four major stores?

Answer 26

The further down in capacity, the shorter the residence time

Question 27

What is the atmosphere’s ability to hold water linked to?

Answer 27

Temperature