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Climate and Weather: Principles of Climate and Meteorology:

Drought

   

Droughts are among the most serious consequences of water scarcity. Scientists define four types of drought, as described in the box below:

Box 1:  Definitions for Various Drought Types

Meteorological drought is a reduction in rainfall compared with the average over a specified period. A drought is said to occur when a large area receives rainfall less than 75% of normal for an extended period.

Agricultural drought is inadequate supply of the moisture required by a crop during each different growth stage, resulting in impaired growth and reduced yields.

Hydrological drought is the impact of a reduction in rainfall on surface and underground water resources that reduces the supply of water for irrigation, hydro-electrical power generation, and other household and industrial uses.

Socio-economic drought relates to the impact of drought on human activities, including both indirect and direct impacts on agricultural production and the wider economy. 

Source: INGC/ FEWS NET Mind 2003

 

Dams such as Vanderkloof can provide a buffer in drought conditions.
Source:Pyke 2003
( click to enlarge )

The frequent occurrence of El Niño Southern Oscillation (ENSO) phenomena complicates the expected rainfall pattern that is normally controlled by the movement of the Inter-Tropical Convergence Zone (ITCZ).

Economic development in developing countries is currently threatened by weather-related disasters such as floods and droughts. Water shortages can seriously harm the economy of a country or region, con­straining development and reducing economic growth as financial and hydrological resources are expended to counter the drought. Multi-year droughts can have a lasting legacy, resulting in long-term suffering for agriculturally dependent rural communities and reducing national and regional growth rates significantly.

The map below shows satellite-based measurements of vegetation as an indicator of water stress and drought occurrence in 2007.

Satellite-based measurements of vegetation as an indicator of drought from 2007 (see description below).
Source:NASA GIMMS Group at Goddard Space Flight Center 2007
( click to enlarge )

Box 2: Drought in Southern Africa 2007

Hot, dry weather from January through March 2007 wilted crops in southern Africa. The severe drought produced near-record temperatures that, combined with a lack of rainfall, caused extensive crop damage, particularly in western crop areas, reported the United States Department of Agriculture’s Foreign Agricultural Service. In South Africa, the anticipated yield from the corn crop dropped from ten million tons in December to six million tons in April because farmers couldn’t plant in the dry conditions and many of the crops that were planted wilted in the dry heat. The last South African drought of this magnitude occurred in 1992.

The impact of the drought on vegetation throughout southern Africa is illustrated in this image. The image shows vegetation conditions in March 2007 compared to conditions during the average March between 1999 and 2006 as measured by the SPOT satellite. Brown areas show where plants were less thick or where fewer plants grew than average. Green areas, by contrast, indicate that vegetation was thicker and more lush than average.

Source: NASA Earth Observatory 2010

 

Impacts of Drought

Drought is often seen as simply an agricultural and food supply issue, but studies have shown that the impacts of droughts are far-reaching, with significant economic, environmental and social impacts. The table below, adapted from Vogel, Laing and Monnik (1999), summarises the impacts of drought in Southern Africa, these issues are relevant to drought vulnerable areas around the world.

Table: Impacts of drought in southern Africa

Primary impacts

Secondary impacts

Social

Disrupted distribution of water resources

Migration, resettlement, conflicts between
water users

Increased quest for water

Increased conflicts between water users

Marginal lands become unsustainable

Poverty, unemployment

Reduced grazing quality and crop yields

Overstocking; reduced quality of living

Employment lay-offs

Reduced or no income

Increased food insecurity

Malnutrition and famine; civil strife and conflict

Increased pollutant concentrations

Public health risks

Inequitable drought relief

Social unrest, distrust

Increased forest and range fires

Increased threat to human and
animal life

Increased urbanization Social pressure,
reduced safety

 

Environmental

Increased damage to natural habitats

Loss of biodiversity

Reduced forest, crop, and range land
productivity

Reduced income and food shortages

Reduced water levels

Lower accessibility to water

Reduced cloud cover

Plant scorching

Increased daytime temperature

Increased fire hazard

Increased evapotranspiration

Crop withering and dying

More dust and sandstorms

Increased soil erosion; increased air
pollution

Decreased soil productivity

Desertification and soil degradation
(topsoil erosion)

Decreased water resources

Lack of water for feeding and drinking

Reduced water quality

More waterborne diseases

Economic

Reduced business with retailers

Increased prices for farming commodities

Food and energy shortages

Drastic price increases; expensive
imports/substitutes

Loss of crops for food and income

Increased expense of buying food, loss of income

Reduction of livestock quality

Sale of livestock at reduced market price

Water scarcity

Increased transport costs

Loss of jobs, income and property

Deepening poverty; increased unemployment

Less income from tourism and recreation

Increased capital shortfall

Forced financial loans

Increased debt; increased credit risk
for financial institutions

Source: FAO 2004, adapted from Vogel, Laing and Monnik (1999)

 

 

 

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