Drought

What is drought?

• A drought is an extended period of dry weather leading to extreme dryness.

• This results in a shortfall of water supply which has hydrological and agricultural impacts.

• Drought is different from most other hazards as it develops slowly as a creeping hazard.

• Aridity and desertification are associated with drought but they are not the same.

• Drought is characterised by moisture levels below normal for the area affected.

Types of drought

We can define drought in three main ways:

· Meteorological drought: related to rainfall amounts

· Hydrological drought: determined by water levels in reservoirs

· Agricultural drought: related to the availability of water for crops 

The impacts

• Humans are conditioned to live with the average rainfall conditions therefore in times of drought we suffer.

• Evapotranspiration, run off and infiltration will help determine the impact of the drought.

• A drought may occur within a few weeks without rain in a humid area but will take longer to occur without rain in a arid area.

• We might define drought in Libya as occurring when annual rainfall is less than 180 mm, but in Bali, drought might be considered to occur after a period of only 6 days without rain

Causes of drought

• The initial cause of drought is associated with a change in atmospheric conditions brought about by:

1. Persistent high pressure

2. El Nino and a change in ocean temperatures

3. Changing depression tracks

However droughts are very much exacerbated by

Characteristics of drought

• Not confined to a specific geographic location• Semi arid areas are most prone: Sahel, Great Plains

USA, Australia.• Severity of droughts is intensifies by over cropping,

overgrazing, deforestation• Mismanagement of arid lands is often related to

economic development. This is often made worse by debt or dependence on cash crops for foreign income.

• Also rapid population growth can have a direct impact upon the size of drought and the magnitude of this natural disaster.

Characteristics continued

• Each drought has its own unique characteristics and there is no scale of magnitude exists

• On its own meteorological drought may not be a hazard if water supply systems can meet demand

• Drought may result in secondary natural hazards such as dust storms, malnutrition related disease, locusts and wildfires

• Severe agricultural drought can result in debt and famine

Drought in the Middle East 2007-now