EQ2 - Factors influencing the Hydrological cycle Flashcards
What is meteorological drought?
A deficiency of water over an extended period
What is hydrological drought?
Where there is reduced stream flow, lowered groundwater levels and reduced water stores
What is agricultural drought?
When soil moisture is reduced, affecting agriculture
What is a deficit (when input is less than output) in the hydrological system, better known as?
A drought
What are the 4 main characteristics of Meteorological Drought?
- Low Precipitation
- High temperatures
- Strong winds
- Increased solar radiation
What are the 3 main impacts of meteorological drought?
- Loss of soil moisture
- Less water for irrigation (agriculture)
- Less water for consumption (domestic)
What are the 3 main characteristics of hydrological drought?
- Reduced infiltration
- Low soil moisture
- Little percolation and groundwater recharge
What are the 4 main impacts of hydrological drought?
- Reduced storage in lakes/reservoirs
- Less water for urban supply
- Poor water quality
- Wetland habitats threatened
What are the 3 main characteristics of agricultural drought?
- Low evapotranspiration
- Reduced biomass
- Fall in groundwater level
What are the 5 main impacts of agricultural drought?
- Poor yields for rainfed crops
- Failing irrigation systems
- Government aid may be needed to support rural industries
What are the 4 main socio-economic impacts associated with drought?
- Food shortages (due to agriculture failure)
- Rural economy collapse
- Rural-urban migration
- Wildfires
What process can begin to occur during extended periods of drought?
Desertification
What is El Niño? (ENSO)
The slackening/reversal of trade wind patterns
Typically (in a non ENSO period) where are cool/warm waters found?
(in the pacific)
Cold water along Peruvian Coast
Typically warm water around Australia
How does the pattern of cold water (Peru) and warmer water (Australia) switch during El Niño?
Complete reversal - Australia cold, Peru Warm
How often, and for how long, do ENSO cycles typically last?
Occur every 3-7 years
Last around 18 months
The harvest of which fish in Peru is usually indicative of ENSO occurrence?
Anchovies
- They prefer cold waters
- When ENSO warms water in Peru, Anchovy harvest usually falls
How does ENSO affect areas such as South East Asia, East Australia and North-East Brazil?
Causes extremely dry conditions
In a non El Niño Year, what direction do trade winds blow?
East to West (along the equator)
What seasonal storms in India and South East Asia often fail in El Niño periods?
Monsoons
What events can sometimes (but not always) follow an El Niño event?
La Nina
Explain the La Niña process
The build-up of cooler-than-usual subsurface water in the central/eastern Pacific
What function do Wetlands serve within the Hydrological system?
Act as temporary water stores, helping to mitigate river floods
Chemically, how do Wetlands help to maintain river quality?
Act as Water Filters
- Trap and recycle nutrients and pollutants
Wetlands have a low biological productivity and support a limited food web
True or False?
False
- they support a diverse food web, home to fish and migrating birds
How does Meteorological drought impact wetlands?
Less precipitation causes vegetation to die
- affects soil nutrients
- disrupts complex food web
Define Desertification
Once-productive land gradually becomes unable to support plant/animal life
Desertification is not irreversible
True or False?
True - in some cases it can be reversed
Explain the first stage of desertification
- Less reliable rainfall, both seasonally and annually
- Drought can now sometimes extend into multi-year periods
Explain the second stage of desertification
- Vegetation death
- this leaves soil exposed and vulnerable
Explain the third stage of desertification
- Soil Erosion
- without protection from vegetation, bare soil is eroded by wind
Explain the fourth (final) stage of desertification
- Rain intensity issues
- When rain eventually does fall, it is in short bursts
- Decertified soil struggles to absorb/store the water
How much less rainfall, compared to historical averages, is the Northern Sahel currently experienced?
30-40% less rainfall than usual
Whilst the Northern Sahel is getting 30-40% less rainfall than usual, the central/southern Sahel is mostly unaffected
True or False?
False - issues are widespread
- Central Sahel 25-30% less
- Southern Sahel 20-25% less
How is population growth in vulnerable areas enhancing desertification?
Greater demand for food, water and resources places additional stress on the land
How is the intensification of cattle farming enhancing desertification/drought?
- Large areas of forest cleared for grazing land, exposing soils
- Overgrazing kills vegetation and reduced the ability for the land to recover
How is the intensification of crop farming enhancing desertification/drought?
- Time between harvests reduced to keep up with food demand
- Shorter ‘fallow’ periods prevents the soil from regenerating, reducing fertility
How is deforestation enhancing desertification/drought?
Removes the root systems that stabilises soil
- soil more vulnerable to erosion and becomes infertile
Desertification is an example of what type of feedback loop?
Positive feedback loop - initial change triggers processes that amplify impacts