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Drought is generally known as a continuous period of dry weather. The causes of
droughts can be natural or anthropogenic. In most cases such as the Dust Bowl
in the US, the causes of droughts can be a combination of both natural and
anthropogenic factors. Due to the nature of drought and human factors, there will
be problems in managing an inhabited environment prone to droughts.
The natural causes of drought include the shifting of rain belts and El Nino
Southern Oscillation (ENSO). The Intertropical Convergence Zone (ITCZ) can
shift north or south depending on the movement of the overhead sun and
according to which hemisphere is experiencing summer. This affects the location
of the descending limb of the Hadley cell, which will result in the formation of
subtropical high pressure belts around 20-30 degrees North and South of the
Equator. The area under this zone will experience descending air. The air
strongly subsides and warms adiabatically by compression. As a result, the air
cannot cool to saturation point and this inhibits condensation. Cloud formation is
suppressed, which results in little precipitation. The size of this area varies from
year to year. If the air sinks over a larger area than normal, droughts can occur,
particularly along the edges of deserts. An example is the Sahel, which is located
along the southern edge of the Sahara
El Nino is used to describe an extensive warming of the upper ocean in the
tropical eastern Pacific lasting up to a year or even more. It is linked with a
change in atmospheric pressure known as the Southern Oscillation (SO). During
an El Nino event, there is a reversal of normal conditions in pressure,
precipitation and often winds and ocean currents in the Equatorial Pacific region.
Instead of pressure rising over the Eastern Pacific and falling over the Western
Pacific, it now rises over the Western Pacific and descends over Eastern Pacific.
This allows the ITCZ to migrate southwards and causes the trade winds to
weaken in strength or sometimes, even to be reversed in their directions. The
descending air is now over South-east Asia and gives that region much drier
conditions than it usually experiences, and on extreme occasions, even causing
drought. Bangladesh was one of the most affected areas in El Nino events.
During the 1997-98 El Niño, Bangladesh experienced a 60% rainfall deficit in
June 1997.Consequently, the southeast monsoon wind was delayed by one
month and the country faced a short drought condition.
One of the major anthropogenic causes of droughts is the rise in population
densities. This leads to an increase in demand for food, which results in the
progressive conversion of natural ecosystems into farmland and has contributed
to desertification. This is mainly due to unhealthy farming practices such as the
overcultivation of croplands, shortening of fallow seasons, overgrazing of
rangelands, mismanagement of irrigated cropland and desertification.
Desertification is the permanent transformation of the land surface by human
activities to resemble a desert. For example, the US Dust Bowl was caused by
sustained drought conditions and worsened by years of land management
practices that left topsoil susceptible to the forces of the wind. The soil, depleted
of moisture, was lifted by the wind into great clouds of dust and sand which were
so thick they concealed the sun for several days at a time. They were known as
"black blizzards”.
The greenhouse effect is a naturally occurring phenomenon which people have
known about since the mid-19th century. Greenhouse gases in the atmosphere
such as carbon dioxide absorb long wave radiation from the Earth’s surface. This
helps to warm the Earth and maintain temperatures that enable life to exist. As
human activities have continually increase the amount of greenhouse gases in
the air, the greenhouse effect is escalating and global temperatures are rising.
This phenomenon is known as global warming. It may cause climate boundaries
to shift their positions, making some regions wetter while others become drier.
Also, global warming may increase the frequency of El Nino, which would worsen
drought conditions.
The management of an inhabited environment prone to droughts focuses on
three aspect: prediction, mitigation and response.
Prediction involves the use of instrumental records of drought, which are
observed data measured by weather monitoring instruments. Such a prediction
method is being adopted in the US. They reveal the short-term behavior (less
than 100 years) and spatial patterns of drought, helping scientists learn more
about the character of droughts. Although these records include the major 20th
century droughts, they are too short to assess the reoccurrence of major
droughts such as those in the 1930s to 1950s. As a result, this provides a
general prediction rather than the occurrence of specific droughts. Moreover,
drought is a creeping phenomenon. It develops slowly over large areas and an
extended period of time. Hence, droughts are much more difficult to identify.
Mitigating of droughts in inhabited areas include measures such as the reduction
in herd numbers. When feed resources are getting short, one solution is to
critically evaluate the members of the herd and eliminate those that are less
useful. Sale or agistment (relocating herd to non-affected pastures) are the two
options available to reduce stock numbers. Although such measures can
decrease the pressure on land in the short run as less amount of food is needed
to feed smaller herd numbers, this may be detrimental in the long run. This is
especially so if the area experiences food insecurity as droughts result in crop
failure. Under such circumstances, the livestock can serve as food for the people.
If a reduction in herd numbers occurs, there will be a greater reduction in food
supply and this can lead to a host of problems such as starvation. During the
1968 to 1974 Sahelian drought, grain crops failed and foraging cattle could find
no food to eat. In the worst stages of the drought, nomadic cattle herders had to
sell their remaining cattle. As the cattle were their sole means of subsistence, the
nomads soon starved.
One of the aspects of response to drought in an inhabited area is food aid. This
is one of the most important humanitarian responses of the international
community, in relation to drought. For some LDCs, food aid has become almost
synonymous with drought relief. During the 2002 drought in South Africa,
charities such as CARE responded with food aid and emergency water supplies
to help solve immediate problems of malnutrition and drinking water. However,
food aid may not necessarily prevent famine-related deaths. This is because
famine-related deaths are highly age-specific and are dependent on other factors
such as the presence of endemic disease. For example, over 20% of people in
South Africa are HIV positive. People who are HIV positive often lack energy to
grow food, conserve water and cope with drought. AIDS can also make
malnutrition worse. Thus, they are unable to sustain themselves. In such
situations, these people require immediate medical attention besides food aid.
Without medical aid, food aid can be deemed as ineffective in the long run.
In conclusion, the causes of droughts can vary from natural to anthropogenic or
even a combination of both. Due to the nature of drought and the human factors
involved, problems are encountered in the management of drought in an
inhabited environment.