Water EQ2 - 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, which decrease because of reduced precipitation inputs and continued high evaporation rates
MAJOR IMPACTS - reduced storage in lakes and reservoirs, poorer water quality
What is agricultural drought and what are its major impacts?
The rainfall deficiency from meteorological drought leads to 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
Why are droughts known as creeping hazards?
They typically have a long period of onset, sometimes several years (it is difficult to determine whether it is a drought or dry period initially)
What are some of the measurements of drought?
- Palmer Drought severity index
- Crop moisture Index
- Palmer Hydrological drought index
How does the Palmer Drought Severity Index measure 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?
El Nino refers to the increase in sea-surface temperatures that periodically 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 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 are the human and physical causes of desertification?
HUMAN - overgrazing, overcultivation and deforestation (due to increase in animals and population)
PHYSICAL - less rainfall and global warming
These factors lead to a removal of vegetation and therefore an increase in evaporation from the soil, leading to increased risk of soil erosion
What is a wetland?
A distinct ecosystem that is flooded or saturated by water, either permanently or seasonally, acting as a temporary store in the water cycle
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 when the level of water in rock or soil rises above the ground (water table rises)
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?
- 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
What are the environmental impacts of flooding?
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
What is eutrophication?
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
What will the impact of climate change be on the hydrological cycle?
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
Why is modelling climate change trends complex?
- 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
How can climate warming modify the hydrological cycle?
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
What is the impact of climate change on hydrological cycle inputs/outputs?
- higher temp = more evaporation
- decreasing rainfall in some areas of the world
- more intense precip in many areas due to enhanced moisture holding capacity
What is the impact of climate change on hydrological cycle stores/flows?
- loss of snow and glaciers as cryosphere stores
- depleted aquifers
- change in wetland capacity
- increased evaporation from oceans
How has the moisture holding capacity of the atmosphere been changing?
Increasing by a rate of about 7% per degree Celsius of climate warming, therefore creating the potential for heavier precipitation
How has flooding changed with climate change?
Despite hydrological cycle intensifying, documented flood figures show no clear evidence of trends in increasing freq or magnitude of flood events globally
How have droughts changed with climate change?
Climate change influences precip, temp and EVT rates - and therefore occurrence and severity of droughts
In past 30 years, droughts have become more widespread, more intense and more persistent: but it is hard to disentangle impacts of climate change from human influences
What are the impacts of short term climate change on water supply?
- increase in annual temp leads to great evaporation from surface water and reservoirs
- greater EVT rates, desiccation of forests store
- unreliable rainfall patterns due to oscillations like ENSO
- depleted aquifers leads to problems with groundwater
- decreasing rainfall
- loss of snow and glaciers
- increased intensity and freq of droughts
