Water EQ2 Flashcards
What is the definition of a drought?
A shortfall or deficiency of water over an extended time period
What are the three major types of drought?
- meteorological drought
- agricultural drought
- hydrological drought
What is a meteorological drought?
Shortfalls in precipitation as a result of short terms variability within the longer terms average total.
What are the causes of a meteorological drought?
- natural variation in atmospheric conditions
- desiccation caused by deforestation
- El Niño events (ENSO cycle)
- climate changes
What are the features and impacts of a meteorological drought?
Features
- low precipitation
- high temps
- strong wind
Impacts
- loss of soil moisture
- supply of irrigation water decline
What is a hydrological drought?
Associated with reduced stream flow and groundwater levels, which decrease sue to reduced precipitation and high evaporation rates.
What causes a hydrological drought?
- reduced precipitation inputs
-high evaporation rates - ENSO cycles
- climate change
What are the conditions during a El Niño event and how do they led to drought?
In an El Niño event trade winds are slackened or reversed reversing the air circulation loop.
This results in the cool water is replaced by warm water upwelling in Peru and the warmer water in Australia replace by cool water. This triggers a change in precipitation patterns throughout the world. The warmer upwelling of water lead to high rates of evaporation (lowering water table) but also creating more moist air and therefor changes in precipitation levels E.g failure in monsoon rains in India.
What’s are the conditions in a La Niña event and how do they led of drought?
La Niña event are associated with a exaggerated version of a normal years with a very strong Walker loop. It create drought due to the build up of cool water in the tropical part of the pacific.
What is a famine drought?
A humanitarian crisis in which the widespread failure of agriculture systems lead to food shortages and famines with massive socioeconomic and environmental impacts.
What is agricultural drought?
When rainfall deficiency from a meteorological drought leads to deficiency of soil moisture and soil water availability having a knock of effect on plant growth.
How does human activity has led to droughts?
The contribution of human activity such as
- deforestation (transpiration)
- urbanisation (Over extraction due to population growth)
- climate change
Do not cause drought but can enhance the effects and impacts acting like a positive feedback loop.
How has human influences made drought conditions more severe in the Sahel?
The main physical cause of drought in the Sahel region is the changing rainfall patterns that are very unreliable and semi arid conditions.
Human factors act like a feedback loop enhancing the impacts through the over extraction of surface and ground water due to
- population growth
- over grazing (destroying veg cover)
- deforestation (fuel wood)
Causing severe desertification.
droughts in Australia
Drought is a recurrent feature in Australia which are becoming more severe and frequent. The physical factors are El Niño crewing rainfall deficiency’s.
The big dry in 2006 is an example of a severe drought creating several impacts
- aquifers fell to 40% of their capacity
- completions over water between urban dwellers and farmers
Australia has managed their droughts by carful water management schemes, large scale grey water recycling and desalination plants.
What are the main ecosystems effected by droughts?
- wetland
- forest stress
What is a wetland and why are they valuable?
A wetland is a are4s covered or saturated with water, they cover 10% of the earths surfaces and are extremely valuable as
- act as temporary water stores
- recharging aquifers
- very high biological productively supporting diverse food webs (feeding sites for migrating birds)
- filters and maintain water quality (trapping pollutants)
How do droughts affect wetlands?
Less precipitation there will be less interception, infiltration and percolation causing the vegetation to become stressed and the water table to fall due to increased evaporation. This will reduce the valuable functions performed from the wetlands.
How are forest ecosystems impacted in a drought?
Drought not only cause direct physical damage to forest through the starvation of water but also increases the susceptibility of lines and firs to fungal diseases increasing tree mortality. As well as this there is and increased threat of forest fires this both destroy habitats and decrease carbon stores. Reduces there role in the hydrological cycle (interception and transpiration).
What is ecological resistance?
The capacity of an eco systems to withstand and recover from a natural event or some forms of human disturbance.
What are the meteorological causes of flooding?
- intense storms (flash flooding)
- prolonged heavy rainfall (Asian monsoon or deep depression across the UK)
- rapid snowmelt or jokulhaulps.(Siberia)
What is the definition of flooding?
A surplus within the hydrological cycle leading to high flows of water in a drainage basin. Flooding occurs when the amount of discharge causes a body of water to overflow its channels and submerge the surrounding land.
Why is Bangladesh particularly flood prone?
- land consisting of floodplain and deltas build up by major rivers such as the Ganges
- meltwater from the Himalayas
- summer monsoons
- prone to storm surges
What physical factors increase the risk of flooding?
- low lying areas with impermeable surfaces
- impermeable rocks
- vegetation amount
- high gradient slopes
- shallow soil depth
What human actions increase the risk of flooding?
- urbanisation
- damn building
- downslope ploughing
- river mismanagement
- deforestation
