Lesson 6 - Causes of Drought Flashcards
Define drought
Period of deficient rainfall relative to the statistical multi year average for a region
What are the 4 types of drought?
Meteorological
Agricultural
Hydrological
Socio-Economic
When does meteorological drought occur?
Precipitation lower than usual
But no threshold for the rain deficit that turns a dry spell into an official drought
When does agricultural drought occur?
Insufficient soil moisture to meet needs of a particular crop at particular time
Caused by reduced groundwater, evapotranspiration changes etc.
When does hydrological drought occur?
Deficiencies in surface + subsurface water supplies
As measured in rivers, reservoirs, lakes + groundwater
When does socio-economic drought occur?
Water demand exceeds availability
Supply diminished by weather, overuse etc.
What are the natural causes of drought in the short term?
Reduced soil moisture
Blocking anticyclones
What are the natural causes of drought in the medium term?
ENSO cycles
Hydrological factors
What are the natural causes of drought in the long term?
Global atmospheric circulation
Climate change
Explain the natural short term causes of drought
Soil Moisture - Poor precipitation + high evaporation
Plants use water quickly, no infiltration
Anticyclones - Polar Front Jet Stream moves Northwards
Stable, hot weather follows
Explain the natural medium term causes of drought
ENSO - El Nino causes drought in Western Pacific
La Nina causes drought in Eastern Pacific
Hydrological - Reduced precipitation
River + groundwater supplies diminish
How does Global atmospheric circulation create drought?
Descending air creates hot + cold deserts
Hot deserts occur between Hadley + Ferrel cells
Cold deserts occur between Polar cells
How does climate change create drought?
Higher temperatures are changing atmospheric systems
Rainfall events becoming more intensive
Higher sea temperatures, changes evaporation + wind patterns
Rain bearing winds may fail
What are the primary human causes of drought?
Irrigation
Water abstraction
Deforestation
Leisure
Dams/Reservoirs/Water Transfers
