Droughts

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Droughts

• School Abdallah Al-Alayly
• Teacher Ms. Abeer Abdallah
• Prepared by Grade 9 students

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Definition of Droughts

• Drought is a normal, recurrent feature of
  climate, although many erroneously consider it a
  rare and random event. It occurs in virtually all
  climatic zones, but its characteristics vary
  significantly from one region to another. Drought
  is a temporary aberration it differs from
  aridity, which is restricted to low rainful
  regions and is a permanent feature of climate.

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The Nature of Droughts

• Drought is essentially an imbalance of the
  hydrologic cycle. In this cycle, water vapor
  enters the atmosphere by evaporation from oceans,
  lakes, and ground surfaces and by transpiration
  from plants. Water is returned to the earth in
  the form of rain or snow. Some of it recharges
  the soil moisture, some accumulate in bodies of
  water, and some runs off to the oceans. Thus
  drought can result simply from a deficiency in
  precipitation over a period of time, or it maybe
  caused or by excessive evaporation and
  transpiration.

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Causes of Drought

• lack of a precipitation
• high temperature, strong wind, and low humidity
  all of which increase the loss of moisture
• shifting of normal cyclone (low pressure storm
  system) tracks across a region
• High pressure systems in which cold, dense air
  sinks and is warmed by compression
• abnormally low sea surface temperature
• Human activities also contribute to the
  development of drought conditions poor cropping
  methods and improper soil conservation techniques
  often contribute to create the drought.

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Effects of Droughts

• Primary effects
• Primary effects of drought result from a lack of
  water. As a dry period progresses and water
  supplies dwindle, existing water supplies are
  overtaxed and finally dry up. The primary losses
  are loss of crops low of livestock and other
  animals, and loss of water for hygienic and
  drinking.
• Secondary effects of drought
• As water supplies swindle and crops and fodder
  are depleted, families begin to migrate in search
  of better grazing lands for their herbs or move
  to cities to seek jobs and alternative sources of
  income.
• The migration may, in itself, contribute to
  spreading the scope of the disaster, especially
  if grazing animals are moved with people.
• If drought is long term, it may result in
  permanent changes of settlement, social, and
  living patterns
• major ecological changes, such as increased scrub
  growth, increased flash flooding and increased
  wind wing erosion of soils.

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Examples

• Bolivia
• The drought during 1983 had affected large areas
  of 7 of the Bolivias nine departments, 80 of
  crops were lost. 35 of Bolivias total land area
  was directly affected. The drought deprived 1.6
  million peasant farmers to their source of income
  and food supply.Total agricultural losses were
  estimated at U.S. 417.2 million.
• Cambodia
• Cambodian farmers plant rice seedlings into a
  bone dry paddy field in Kampong Speu province, 25
  miles west of Phnom Penh. Rice production is
  being hit by the worst drought in 20 years.