5.2- short & long-term variations in the hydrological cycle

Question 1

What are the four types of drought?

Answer 1

Meteorological, hydrological, agricultural, famine

Question 2

What is meteorological drought and what are it’s main impacts?

Answer 2

Shortfalls in precipitation as a result of short term variability within the longer term average overall.
MAJOR IMPACTS - loss of soil moisture, supply of irrigation water declines

Question 3

What is hydrological drought and what are it’s main impacts?

Answer 3

Associated with reduced stream flow and groundwater levels -> decrease because of reduced precipitation inputs and continued high evaporation rates
MAJOR IMPACTS - reduced storage in lakes and reservoirs, poorer water quality

Question 4

Name 5 characteristics of a meteorological drought

Answer 4

RAINFALL DEFICIT
-low precipitation
-high temperature
-strong winds
-^ solar radiation
-reduced snow cover

Question 5

Name 4 characteristics of a hydrological drought

Answer 5

STREAMFLOW DEFICIT
-reduced infiltration
-low soil moisture
-little percolation
-little groundwater recharge

Question 6

What is agricultural drought and what are its major impacts?

Answer 6

The rainfall deficiency from meteorological drought -> deficiency of soil moisture and soil water availability which reduces biomass
MAJOR IMPACTS - poor crop yields, failure of irrigation systems, rural industries affected

Question 7

What is famine drought and what are its major impacts?

Answer 7

A humanitarian crisis in which the widespread failure of agricultural systems leads to food shortages and famines with severe social, economic and environmental impacts
MAJOR IMPACTS - rural to urban migration as rural economy collapses, aid required, increased malnutrition

Question 8

Name 4 characteristics of an agricultural drought

Answer 8

SOIL MOISTURE DEFICIT
-low evapotranspiration
-plant water stress
-reduced biomass
-fall in groundwater levels

Question 9

Name 4 characteristics of a famine drought

Answer 9

FOOD DEFICIT
-loss of natural vegetation
-^ risk of wild fires
-wind-blown soil erosion
-desertification

Question 10

Name the 3 measurements of drought?

Answer 10

Palmer Drought severity index
Crop moisture Index
Palmer Hydrological drought index

Question 11

How does the Palmer Drought Severity Index measure drought?

Answer 11

applies to long-term drought

-Focuses on monitoring duration and intensity of large scale, long term drought inducing atmospheric circulation

Question 12

How does the Crop Moisture Index measure drought?

Answer 12

measures short-term drought

-on a weekly scale, is useful for farmers to monitor water availability during the growing season

Question 13

How does the Palmer Hydrological Drought Index measure drought?

Answer 13

Uses different models to monitor hydrological systems responses to drought - both reacting and recovering to it

Question 14

What is El Nino?

Answer 14

the increase in sea-surface temperatures that develop across the east-central equatorial Pacific.

Question 15

What happens during an El Nino year?

Answer 15

trade winds in western Pacific weaken and die, reversing the air circulation loop

this causes a reversal of the warm water which piles up in the eastern Pacific

conditions become calmer across the whole of the Pacific

Question 16

What is La Nina?

Answer 16

La Nina refers to the periodic cooling of sea-surface temperatures across the east-central equatorial Pacific.

Question 17

What happens during a La Nina event?

Answer 17

This is an exaggerated version of a normal year
- trade winds become more strong
- warm water is pushed westwards, leading to heavy rain in southeast Asia due to low pressure conditions
- high pressure develops on the Eastern pacific, leading to drought

Question 18

What happens in a normal year in comparison to an el nino/ la nina year

Answer 18

-trade winds blow from east -> west along equator

-air pushes warm water westwards

-warm, moist air ^, cools, condenses -> rain clouds

-trade winds push warm air westwards

-causes upwelling of nutrient-cold wate, heavy rain

-results in Australasian sea levels being 50cm ^ than Peru & sea temp being 8 degrees warmer

Question 19

What is desertification?

Answer 19

Land degradation in arid, semi-arid and dry sub-humid regions resulting from various factors including climatic variations and human activities

Question 20

Do human factors cause drought?

Answer 20

No, but they act like a positive feedback loop in enhancing its impact

Question 21

What is a positive feedback loop

Answer 21

cyclical sequence of events that ^ change

Question 22

What is negative feedback loop

Answer 22

cyclical sequence of events that neutralises the effects of a system

Question 23

Name 3 ways humans cause desertification

Answer 23

overgrazing -> ^ in animals -> soil depleted of nutrients, no proetctive grass cover

overcultivation -> ^ BR -> more land needed for food -> soil exposed to rain & wind

deforestation -> ^ need for wood for cooking, heating -> fuelwood

Question 24

Name 3 physical causes of desertification

Answer 24

-less rainfall -> rivers, wells dry up -> vegetation dies, no protective cover

-global warming -> ^ temp, ^ evaporation -> less rainfall

Question 25

What is a wetland?

Answer 25

An area of marsh, fen, peatland or water with water that is static or flowing, fresh, brackish or salt

Question 26

What are the key functions of wetlands?

Answer 26

temporary water stores in the hydrological cycle (recharge aquifers)

act like giant water filters by trapping and recycling nutrients and pollutants

high biological productivity by supporting very diverse food web

provide resources and services within water and carbon cycle

Question 27

What are the ecosystems services of wetlands?

Answer 27

Supporting - primary production, nutrient cycling, food chain, carbon cycle
Regulating - flood control, water purification
Provisioning - fuelwood, peat, fisheries
Cultural - aesthetic value, recreational use, cultural heritage

Question 28

Why has there been wetland habitat loss?

Answer 28

Agriculture and urban development
Also water transfer schemes and the exploit of fuel resources such as peat

Question 29

How can drought impact on wetlands?

Answer 29

Limited precipitation = less interception as vegetation deteriorates, transpiration decreases and wetlands become less functional. Desiccation can also accelerate destruction by wildfires.

Question 30

What is flooding?

Answer 30

Flooding occurs when discharge is of a sufficient enough quantity to cause a body of water to overflow it’s channel and submerge the surrounding land

Question 31

What is groundwater flooding?

Answer 31

Flooding that occurs after the ground has become saturated from prolonged heavy rainfall

Question 32

What is surface water flooding?

Answer 32

Flooding that occurs when intense rainfall has insufficient time to infiltrate the soil, so flows overland

Question 33

What is flash flooding?

Answer 33

A flood with an exceptionally short lag time, often minutes or hours

Question 34

What are the physical causes of flooding?

Answer 34

Prolonged and heavy rain associated with the passage of low pressure systems or depressions
Seasonal monsoonal rainfall in Asia
Tropical storms or cyclones
Snow/ice melt and jokulhlaups

Question 35

What are the human actions exacerbating flood risk?

Answer 35

Urbanisation is the main one - creation of impermeable surfaces, artificial conduits speeding up the drainage of water, impeding channel flow
Also changing land use associated with agricultural development - DEFORESTATION

Question 36

What are the socio economic impacts of flooding?

30
Q
What are the environmental impacts of flooding?

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A
Some positives - floods play an important role in maintaining key ecosystem functions and biodiversity by linking river with land surroundings
- recharge groundwater systems
- trigger breeding, migration, dispersal
However intense flooding can lead to eutrophication, polluted waters and erosion

31
Q
What is eutrophication?

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A
Excessive richness of nutrients in a lake or other body of water, leading to a dense growth of plant life and death of animals from a lack of oxygen

32
Q
What will the impact of climate change be on the hydrological cycle?

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A
Most scientists agree that climate change (global warming and oscillations such as ENSO) will result in an intensification, acceleration or enhancement of the global hydrological cycle

33
Q
Why is modelling climate change trends complex?

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A
climate dynamics: interaction of the spheres only partially understood
as a results of teleconnections, it is difficult to distinguish between impacts of oscillations like ENSO and climate warming
global records are very incomplete, making it hard to make predictions
34
Q
How can climate warming modify the hydrological cycle?

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A
Surface heating → increase in evaporation (drought?) → increase in moisture content of atmosphere due to increases in temp → enhanced precip rates → enhanced latent heating and therefore storm intensity → changes in precip amount, distribution, increased flooding

35
Q
What is the impact of climate change on hydrological cycle inputs/outputs?

Answer 36

mortality
post flood morbidity due to spread of water borne diseases
destruction of property and infrastructure
livelihoods affected
crops, livestock and agricultural infrastructure suffer damage
loss of food supplies leading to famine