5.2- short & long-term variations in the hydrological cycle Flashcards
What are the four types of drought?
Meteorological, hydrological, agricultural, famine
What is meteorological drought and what are it’s main impacts?
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
What is hydrological drought and what are it’s main impacts?
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
Name 5 characteristics of a meteorological drought
RAINFALL DEFICIT
-low precipitation
-high temperature
-strong winds
-^ solar radiation
-reduced snow cover
Name 4 characteristics of a hydrological drought
STREAMFLOW DEFICIT
-reduced infiltration
-low soil moisture
-little percolation
-little groundwater recharge
What is agricultural drought and what are its major impacts?
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
What is famine drought and what are its major impacts?
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
Name 4 characteristics of an agricultural drought
SOIL MOISTURE DEFICIT
-low evapotranspiration
-plant water stress
-reduced biomass
-fall in groundwater levels
Name 4 characteristics of a famine drought
FOOD DEFICIT
-loss of natural vegetation
-^ risk of wild fires
-wind-blown soil erosion
-desertification
Name the 3 measurements of drought?
Palmer Drought severity index
Crop moisture Index
Palmer Hydrological drought index
How does the Palmer Drought Severity Index measure drought?
applies to long-term drought
-Focuses on monitoring duration and intensity of large scale, long term drought inducing atmospheric circulation
How does the Crop Moisture Index measure drought?
measures short-term drought
-on a weekly scale, is useful for farmers to monitor water availability during the growing season
How does the Palmer Hydrological Drought Index measure drought?
Uses different models to monitor hydrological systems responses to drought - both reacting and recovering to it
What is El Nino?
the increase in sea-surface temperatures that develop across the east-central equatorial Pacific.
What happens during an El Nino year?
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
What is La Nina?
La Nina refers to the periodic cooling of sea-surface temperatures across the east-central equatorial Pacific.
What happens during a La Nina event?
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
What happens in a normal year in comparison to an el nino/ la nina year
-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
What is desertification?
Land degradation in arid, semi-arid and dry sub-humid regions resulting from various factors including climatic variations and human activities
Do human factors cause drought?
No, but they act like a positive feedback loop in enhancing its impact
What is a positive feedback loop
cyclical sequence of events that ^ change
What is negative feedback loop
cyclical sequence of events that neutralises the effects of a system
Name 3 ways humans cause desertification
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
Name 3 physical causes of desertification
-less rainfall -> rivers, wells dry up -> vegetation dies, no protective cover
-global warming -> ^ temp, ^ evaporation -> less rainfall
What is a wetland?
An area of marsh, fen, peatland or water with water that is static or flowing, fresh, brackish or salt
What are the key functions of wetlands?
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
What are the ecosystems services of wetlands?
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
Why has there been wetland habitat loss?
Agriculture and urban development
Also water transfer schemes and the exploit of fuel resources such as peat
How can drought impact on wetlands?
Limited precipitation = less interception as vegetation deteriorates, transpiration decreases and wetlands become less functional. Desiccation can also accelerate destruction by wildfires.
What is flooding?
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
What is groundwater flooding?
Flooding that occurs after the ground has become saturated from prolonged heavy rainfall
What is surface water flooding?
Flooding that occurs when intense rainfall has insufficient time to infiltrate the soil, so flows overland
What is flash flooding?
A flood with an exceptionally short lag time, often minutes or hours
What are the physical causes of flooding?
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
What are the human actions exacerbating flood risk?
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
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?
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
