Assignment
Name:
Aliza Hamid by group 3
Zainab, ume-habbiba,mlaika,hifza,mursaleen .
Subject:
Environmental science
Topic:
Drought
College:
Superior college mailsi
Submitted to:
Mam Faiza Khalil
Drought:
A drought is a period of drier-than-normal conditions. [1]: 1157 A drought can last for
days, months or years. Drought often has large impacts on
the ecosystems and agriculture of affected regions, and causes harm to the
local economy.[2][3] Annual dry seasons in the tropics significantly increase the
chances of a drought developing and subsequent wildfires.[4] Periods of heat can
significantly worsen drought conditions by hastening evaporation of water vapour,
[5]
drying out forests and other vegetation and increasing fuel for wildfires
Definition
Fields
outside Benambra, Australia suffering from drought in 2006.
The IPCC Sixth Assessment Report defines a drought simply as "drier than normal conditions".[1]:
1157
This means that a drought is "a moisture deficit relative to the average water availability at a
given location and season".[1]: 1157
According to National Integrated Drought Information System, a multi-agency partnership,
drought is generally defined as "a deficiency of precipitation over an extended period of time
(usually a season or more), resulting in a water shortage". The National Weather Service office
of the NOAA defines drought as "a deficiency of moisture that results in adverse impacts on
people, animals, or vegetation over a sizeable area".[11]
Categories
The different categories of droughts have different causes but similar effects:
1. Meteorological drought occurs when there is a prolonged time with less than
average precipitation.[14] Meteorological drought usually precedes the other
kinds of drought.[15] As a drought persists, the conditions surrounding it
gradually worsen and its impact on the local population gradually increases.
2. Hydrological drought is brought about when the water reserves available in
sources such as aquifers, lakes and reservoirs fall below a locally
significant threshold. Hydrological drought tends to show up more slowly
because it involves stored water that is used but not replenished. Like an
agricultural drought, this can be triggered by more than just a loss of rainfall.
For instance, around 2007 Kazakhstan was awarded a large amount of money
by the World Bank to restore water that had been diverted to other nations
from the Aral Sea under Soviet rule.[16] Similar circumstances also place their
largest lake, Balkhash, at risk of completely drying out.[17]
3. Agricultural or ecological droughts affect crop production or ecosystems in
general. This condition can also arise independently from any change in
precipitation levels when either increased irrigation or soil conditions and
erosion triggered by poorly planned agricultural endeavors cause a shortfall
in water available to the crops.
Causes
Contraction and desiccation cracks in the dry earth of the Sonoran desert,
northwestern Mexico
General precipitation deficiency
See also: Precipitation
Mechanisms of producing precipitation include convective, stratiform,[23] and orographic rainfall.
[24]
Convective processes involve strong vertical motions that can cause the overturning of the
atmosphere in that location within an hour and cause heavy precipitation,[25] while stratiform
processes involve weaker upward motions and less intense precipitation over a longer duration.[26]
Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid
water that freezes on contact with the surface, or ice.
Climate change
See also: Effects of climate change on the water cycle and Effects of climate
change on agriculture
Climate change affects many factors associated with droughts. These
include how much rain falls and how fast the rain evaporates again.
Warming over land increases the severity and frequency of droughts
around much of the world. In some tropical and subtropical
[43][44]: 1057
regions of the worldImpacts
Global drought total economic loss risk
Pair of dead oryx in Namibia during the 2018–19 Southern Africa
drought. After years of drought and dust storms the town
of Farina in South Australia was abandoned.
Drought is one of the most complex and major natural hazards, and it has devastating impacts on
the environment, economy, water resources, agriculture, and society worldwide.[18]
One can divide the impacts of droughts and water shortages into three groups: environmental,
economic and social (including health).
Environmental and economic impacts
Agricultural impacts
Further information: Effects of climate change on agriculture
