Causes and types of drought
Cards (6)
- Types of drought
- Meteorological - The degree of dryness compared to 'normal' precipitation
- Agricultural - Insufficient water for crops, so they wilt without irrigation
- Hydrological - Drainage basins suffer shortfalls to precipitation
- Famine - Widespread failure of agricultural systems, food shortages develop into famines that have severe social, economic and environmental impacts
- Causes of meteorological drought
- The physical causes of drought are only partially understood. They lie somewhere in the complex interactions between atmosphere, oceans, cryosphere, biosphere and the land, which produces the climates of the globe.
- Droughts can range from short-term and localised precipitation deficits to longer-term trends that are part of climate change.
- Research suggests that sea surface temperature anomalies are an important causal factor in short-term precipitation deficits.
- Meteorological drought
- Rainfall deficit
- Low precipitation
- High temperatures
- Strong winds
- Increased solar radiation
- Reduced snow cover
- Major impacts:
- Loss of soil moisture
- Supply of water irrigation declines
- Hydrological drought
- Stream flow deficit
- Reduced infiltration
- Low soil moisture
- Little percolation and groundwater recharge
- Major impacts:
- Reduced storage in lakes and reservoirs
- Less water for urban supply and power generation
- Poorer water quality and threats to wetlands and wildlife
- El Niño Southern Oscillation (ENSO)
- Normal Conditions:
- Trade winds blow east to west along the equator.
- Warm water pushed westward; cool water upwelling near Peru.
- Warm, moist air rises, forming rain clouds.
- El Niño Event:
- Trade winds disrupted, may slacken or reverse.
- Warm water moves to the coast of Peru; cool water shifts to near Australia and Indonesia.
- Occurs every 3-7 years, lasts about 18 months.
- Triggers global dry conditions, affecting monsoon rains in India and Southeast Asia.
- La Niña
- La Niña events may sometimes, but not always, follow an El Niño event. They involve the build-up of cooler-than-usual subsurface water in the tropical part of the Pacific. This situation can lead to severe drought conditions, particularly on the western coast of South America.
- Very strong air circulation and very warm water moving east-west.