drought Flashcards
define drought
a period of abnormally dry weather that causes serious hydrological imbalance in an area
- meteorological drought
- agricultural drought
- hydrological drought
- socio-economic drought
- rainfall deficit
- soil moisture deficit
- stream flow deficit (rivers,lakes)
- food deficit (famine)
1 meteorological cause of drought
ITCZ (belt of low pressure around the equator) - area dry when it leaves
Here, air is rising due to sun heating = increased evaporation
2 meteorological cause of drought
Normally - trade winds blow from East (south america, cool water) to West (australasia warmer water).
-temperature difference across equatorial pacific
-upwelling in the east (making water cool)
El Nino - trade winds from equatorial pacific weakened
-cancelling out temperature difference
-interaction between sea & atmosphere
-air over australia = high pressure = drought
- air over s.america = low pressure = floods
La Nina
exaggerated trade winds blowing from east to west of equatorial pacific
- australia = low pressure=intense rainfall =flooding
- s.america= high pressure=drought
Australia 2002-2009 - human causes
- increased water abstraction due to affluence of locations combined with growing populations density, especially at coastal areas
- 40% of drinking water abstracted from rivers
Australia 2002-2009 DROUGHT - natural causes
- effected by El Nino
- large area of country is semi-arid
- unreliable rainfall
- high temp=high evap (from reservoirs)
- risks of climate change 40% drop in rainfall predicted by 2070
The Sahel - human causes
- overgrazing of cattle
- overcultivation of crops
- increasing population density=expansion into drier areas
- lack of understanding
- government growth of cash crops + taxation of animals to force herdsmen to sell
- deforestation 90% of wood used for cooking, increased demand due to oil price ^
The Sahel - natural causes
- annual rainfall concentrated in summer moths
- persistent lack of rain
- rainfall patterns relatively good in 50s-60s encouraging rain-fed agriculture in marginal lands, increasing herd sizes
why are wetlands good?
- 300million organisms depend on it
- flood control, acts as sponge, trapping floodwater and distributing it across the floodplain
- recharges groundwater aquifers
- harmful sediments filtered increasing water quality
- biodiversity of wildlife
impacts of drought on wetland?
- dry up
- loss of habitat
- soil moisture reduced = soil erosion
- eliminate species leaving gap in food web
- organic soils oxidise releasing carbon into atmosphere
why are forests good?
- water storage, regulation of hydrological process
- timber production
- wildlife habitat
- carbon sequestration
impact of drought on forests?
- 2000-2005 drought in US lead to significant die off 90 % of Pinon Pines, major ecosystem changes
- dry conditions left them vulnerable
