EQ2: What factors influence the hydrological system over short- and long-term
timescales?
Types of droughts:
Meteorological drought: dry weather patterns dominating an area, soil moisture decreases and
supply to irrigation decreases.
Hydrological drought: occurs when there is evidence of low water supply, reservoir supply decreases
(water supply issues), water pollution increases, wetland/swamp degradation.
Agricultural drought: lack of moisture in surface soil to support plant life, reduced crop yield,
increased farming costs, grasslands fires.
Famine drought: loss of vegetation, wildfires, desertification, threat to life, severe malnutrition and
aid needed, rural economy is likely to collapse.
ITCZ:
Low pressure band circling the equatorial region of the Earth, rising air that has become unstable
due to the sun heating the Earth and the air.
ENSO:
Normal conditions: Trade winds from east to west pushing warmer water towards Australia,
replaced by cold water by upwelling. Air rises from warmer water causing more clouds and storms,
setting atmospheric conditions.
El Nino: Every 3-7 years, weakened trade winds so less warm water towards the west, rainfall
patterns change causing rain in S America and droughts in Indonesia. Can cause global increase in
temperatures.
La Nina: Strengthening of normal trade winds, increased upwelling, cold water extends out into
centre of ocean, rainfall over Australia.
Desertification in the Sahel region:
- Desertification caused by changing rainfall patterns, lack of vegetation, soil erosion
and wind erosion.
- Sahel: 30% fall in annual rainfall recently
- Human factors: over population, overgrazing, overcultivation and deforestation (Due
to population growth)
- Create pressure on aquifers and underground water supply
- Civil war over water and resources have intensified
Australia:
- Drought a recurrent feature in Australia. 30% of the country rainfall deficient. El Nino
worsens this.
- ‘Big Dry; of 2006 was a 1 in 1000-year event and is associated with long term climate
change. Big problems with droughts.
- Australia, unlike the Sahel, have managed their scarce water resources well.
- Large scale recycling of water, desalination plants, new conservation strategies etc
need to be used. Past over extraction has added to drought severity
Impact of drought on ecosystems:
Wetlands:
