DroughtsDroughts

School: Abdallah Al-Alayly School: Abdallah Al-Alayly

Teacher: Ms. Abeer AbdallahTeacher: Ms. Abeer Abdallah

Prepared by: Grade 9 studentsPrepared by: Grade 9 students

Definition of DroughtsDefinition of Droughts

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

The Nature of DroughtsThe Nature of Droughts

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

Causes of DroughtCauses of Drought lack of a precipitation lack of a precipitation high temperature, strong wind, and low humidity all of which high temperature, strong wind, and low humidity all of which

increase the loss of moisture increase the loss of moisture shifting of normal cyclone (low pressure storm system) tracks shifting of normal cyclone (low pressure storm system) tracks

across a region across a region High pressure systems in which cold, dense air sinks and is High pressure systems in which cold, dense air sinks and is

warmed by compression warmed by compression abnormally low sea surface temperature abnormally low sea surface temperature Human activities also contribute to the development of Human activities also contribute to the development of

drought conditions; poor cropping methods and improper soil drought conditions; poor cropping methods and improper soil conservation techniques often contribute to create the drought.conservation techniques often contribute to create the drought.

Effects of DroughtsEffects of DroughtsPrimary effects:Primary effects: Primary effects of drought result from a lack of water. As a dry Primary effects of drought result from a lack of water. As a dry

period progresses and water supplies dwindle, existing water supplies period progresses and water supplies dwindle, existing water supplies are overtaxed and finally dry up. The primary losses are loss of crops 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 low of livestock and other animals, and loss of water for hygienic and drinking.drinking.

Secondary effects of drought: Secondary effects of drought: As water supplies swindle and crops and fodder are depleted, families As water supplies swindle and crops and fodder are depleted, families

begin to migrate in search of better grazing lands for their herbs or begin to migrate in search of better grazing lands for their herbs or move to cities to seek jobs and alternative sources of income. move to cities to seek jobs and alternative sources of income.

The migration may, in itself, contribute to spreading the scope of the The migration may, in itself, contribute to spreading the scope of the disaster, especially if grazing animals are moved with people. disaster, especially if grazing animals are moved with people.

If drought is long term, it may result in permanent changes of If drought is long term, it may result in permanent changes of settlement, social, and living patterns settlement, social, and living patterns

major ecological changes, such as increased scrub growth, increased major ecological changes, such as increased scrub growth, increased flash flooding and increased wind wing erosion of soils. flash flooding and increased wind wing erosion of soils.

ExamplesExamplesBolivia:Bolivia: The drought during 1983 had The drought during 1983 had

affected large areas of 7 of the affected large areas of 7 of the Bolivia’s nine departments, 80% of Bolivia’s nine departments, 80% of crops were lost. 35% of Bolivia’s crops were lost. 35% of Bolivia’s total land area was directly affected. total land area was directly affected. The drought deprived 1.6 million The drought deprived 1.6 million peasant farmers to their source of peasant farmers to their source of income and food supply.Total income and food supply.Total agricultural losses were estimated at agricultural losses were estimated at U.S. $417.2 million.U.S. $417.2 million.

Cambodia:Cambodia: Cambodian farmers plant rice Cambodian farmers plant rice

seedlings into a bone dry paddy field seedlings into a bone dry paddy field in Kampong Speu province, 25 miles in Kampong Speu province, 25 miles west of Phnom Penh. Rice west of Phnom Penh. Rice production is being hit by the worst production is being hit by the worst drought in 20 years.drought in 20 years.