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Water resources: Use and over exploitation of surface and ground
water – floods, droughts, conflicts over water, dams –benefits and problems
About 97% of the water on the Earth
is salt water and only three per cent (2.5–2.75 %) is fresh water; slightly over two
thirds of this is frozen in glaciers and polar ice caps. The
remaining unfrozen freshwater is found mainly as groundwater, with only a small
fraction present above ground or in the air. 1.75–2% frozen
in glaciers, ice and snow, 0.5–0.75% as fresh groundwater
and soil moisture, less than 0.01% of it as surface water in lakes,
swamps and rivers
Fresh water is a renewable resource,
yet the world's supply of groundwater is steadily decreasing, with depletion
occurring most prominently in Asia, South America and North America, although
it is still unclear how much natural renewal balances this usage, and whether
ecosystems are threatened. Brazil is
estimated to have the largest supply of fresh water in the world, followed
by Russia and Canada
Water uses
Agriculture
It is estimated that 70% of worldwide
water is used for irrigation, with 15-35% of irrigation withdrawals being
unsustainable. It takes around 2,000 - 3,000 litres of water to produce
enough food to satisfy one person's daily dietary need. This is a
considerable amount, when compared to that required for drinking, which is
between two and five litres.
Today, the competition for water
resources is much more intense. This is because there are now seven billion
people on the planet, their consumption of water-thirsty meat and vegetables is
rising, and there is increasing competition for water from industry, urbanization, biofuel crops, and water reliant food items. In the
future, even more water will be needed to produce food because the Earth's
population is forecast to rise to 9 billion by 2050.
Industries
It is estimated that 22% of worldwide
water is used in industry. Major industrial users include hydroelectric
dams, thermoelectric power plants,
which use water for cooling, ore and oil refineries, which use water in chemical processes,
and manufacturing plants, which use water as a solvent. Water withdrawal can be
very high for certain industries, but consumption is generally much lower than
that of agriculture.
Domestic use [house hold]
It is estimated that
8% of worldwide water use is for domestic purposes. These include drinking water, bathing, cooking, toilet
flushing, cleaning, laundry and gardening. Basic domestic water requirements have been estimated
by Peter Gleick at around 50
liters per person per day, excluding water for gardens. Drinking water is water
that is of sufficiently high quality so that it can be consumed or used without
risk of immediate or long term harm. Such water is commonly called potable
water. In most developed countries, the water supplied to domestic, commerce
and industry is all of drinking water standard even though only a very small
proportion is actually consumed or used in food preparation. An assessment of water management in agriculture sector was
conducted in 2007 by the International Water Management Institute in Sri Lanka to see if the world had sufficient
water to provide food for its growing population. It assessed the current
availability of water for agriculture on a global scale and mapped out locations
suffering from water scarcity. It found that a fifth of the world's people,
more than 1.2 billion, live in areas of physical
water scarcity, where there is not enough water to
meet all demands. A further 1.6 billion people live in areas experiencing economic
water scarcity, where the lack of investment in
water or insufficient human capacity make it impossible for authorities to
satisfy the demand for water. In addition, one third of the world's population
does not have access to clean drinking water, which is more than 2.3 billion
people.
Environment
Explicit environment water use is
also a very small but growing percentage of total water use. Environmental
water may include water stored in impoundments and released for environmental
purposes (held environmental water), but more often is water retained in
waterways through regulatory limits of abstraction. Environmental water
usage includes watering of natural or artificial wetlands, artificial lakes
intended to create wildlife habitat, fish ladders, and water
releases from reservoirs timed to help fish spawn, or to restore more natural
flow regimes.
Like recreational usage,
environmental usage is non-consumptive but may reduce the availability of water
for other users at specific times and places. For example, water release from a
reservoir to help fish spawn may not be available to farms upstream, and water
retained in a river to maintain waterway health would not be available to water
abstractors downstream.
Flood
A flood is an overflow of water on land which is usually dry. Sometimes
a water resource (river, lake or pond)
gets flushed with too much water.
Unusually heavy rain sometimes causes floods. When there is too much water, it
may overflow beyond its normal limits. This water then spreads over land,
flooding it. Extreme flooding can also be caused by a tsunami or a
large storm that causes a storm surge. Floods that happen quickly are
called flash floods.
The most deadly flooding was in 1931
in China and killed between 2,000,000 and 4,000,000 people.
During a flood, people try to move
themselves and their most precious belongings to higher ground quickly. The
process of leaving homes in search of a safe place is called evacuation.
During a flood there is plenty of water, but it is
mostly polluted and not safe to drink. If
people drink the dirty water, they may suffer from diseases such as typhoid and cholera.
Flooding is usually caused by a volume of water
within a water body, such as a lake, overflowing. Sometimes a dam breaks,
suddenly releasing a large amount of water. The result is that some of the
water travels to land, and 'floods' the area. Many rivers are in a channel,
between river banks. They flood when the strength of the river causes it to
flow beyond the banks. This is more common at bends or meanders. Flood damage can be prevented by moving away from
places that flood. However, people have long liked to have their homes and
businesses alongside water because water is good for agriculture and transport and
in other ways. Floods are also caused due to improper management of drains.
In 2010 and 2011, Queensland floods hurt Australia's Gross Domestic Product (GDP) by diminishing export revenues. Operations at about 40 coal mines were
disrupted because of the floods. Crops were
damaged and grazing lands were underwater.
The 2015 South Indian floods resulted from heavy rainfall generated by
the annual northeast monsoon in November–December 2015. They affected
the Coromandel Coast region of the South
Indian states of Tamil Nadu and Andhra Pradesh, with Tamil Nadu and the city of Chennai particularly hard-hit. More than 500 people
were killed and over 18 lakh (1.8 million) people were
displaced.
Drought
Causes of drought is due to
1. Precipitation
deficiency, 2. Dry season, 3 El Niño, 4. Erosion and human activities, 5. Climatic
changes
People tend to
define droughts in three main ways:
1. Meteorological drought is brought about when there is a prolonged
time with less than average precipitation. Meteorological drought usually
precedes the other kinds of drought.
2. Agricultural droughts affect crop production or the ecology of
the range. This condition can also arise independently from any change in
precipitation levels when soil conditions
and erosion triggered by poorly planned agricultural endeavors cause a
shortfall in water available to the crops. However, in a traditional drought,
it is caused by an extended period of below average precipitation.
3. Hydrological drought is brought about when the water reserves
available in sources such as aquifers, lakes and reservoirs fall below the statistical average. 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 Sovietrule. Similar circumstances also place their
largest lake, Balkhash, at risk of completely drying out
Consequences of drought
Effects vary according to
vulnerability. For example, subsistence farmers are more likely to migrate
during drought because they do not have alternative food-sources. Areas with
populations that depend on water sources as a major food-source are more
vulnerable to famine.
Drought can also reduce water
quality, because lower water-flows reduce dilution of pollutants and
increase contamination of remaining water-sources.
Drought is a normal, recurring feature of the climate in most
parts of the world. It is among the earliest documented climatic events,
present in the Epic of Gilgamesh and tied to the biblical story of Joseph's
arrival in and the later Exodus from Ancient
Egypt. Hunter-gatherer migrations in 9,500 BC
Chile have been linked to the phenomenon, as has the exodus of early
humans out of Africa and into the
rest of the world around 135,000 years ago.
Water conflict
11% of the global population, or 783 million people, are still without access to
improved sources of drinking water which provides the catalyst for
potential for water disputes.
Water conflicts can occur on the intrastate and interstate levels. Interstate
conflicts occur between two or more neighboring countries that share a
trans-boundary water source, such as a river, sea, or groundwater basin. Recent humanitarian catastrophes, such
as the Rwandan
Genocide or the war in Sudanese
Darfur, have been linked back to water conflicts.
According to UNESCO, the current interstate conflicts occur mainly in the
Middle East (disputes stemming from the Euphrates and Tigris Rivers among Turkey, Syria, and Iraq; and the Jordan
River conflict among
Israel, Lebanon, Jordan and the State of Palestine), in Africa (Nile
River-related conflicts among Egypt, Ethiopia, and
Sudan), as well as in Central Asia (the Aral
Sea conflict among Kazakhstan, Uzbekistan,
Turkmenistan, Tajikistan and Kyrgyzstan). At a local level, a remarkable
example is the 2000 Cochabamba protests in Bolivia, depicted in the 2010 Spanish film Even the Rain by Icíar Bollaín.
Dams - Benefits and problems
Dams
are built across rivers to store water for irrigation, hydroelectric power
generation and flood control. The dams built to serve more than one purpose are
called "multi-purpose dams". These dams were called the "temples
of modern India" by the country's first Prime Minister, Jawaharlal
Nehru.
Benefits
of dams are
1. Dams are built to
control flood and store flood water
2. Sometimes dams are
used for diverting part or all of the water from river into a channel.
3. Dams are used mainly
for drinking and agricultural purposes.
4. Dams are built for
generating electricity
5. Dams are used for
recreational purposes
6. Navigation and
fishery can be developed in the dam areas
Problems of dams
Dams may face
problems upstream or downstream as listed below:
a.
Upstream
problems
1. Displacement of
tribal people
- Loss
of non-forest land
- Loss
of forests, flora and fauna
- Landslides,
sedimentation and siltation occurs
- stagnation
and waterlogging around reservoirs retards plant growth
- Breeding
of vectors and vector-borne diseases
7. Reservoir Induced
Seismicity (RIS) causes earthquakes
b.
Downstream
problems
- Water
logging and salinity due to over irrigation
- Reduced
water flow and silt deposition in rivers
- Salt
intrusion at river mouth
- Since
the sediments carrying nutrients gets deposited in the reservoir, the
fertility of the land along the river gets reduced
- Due to structural
defects or faulty design of the dam may cause sudden dam failure leading
to collapse and destruction to life and property.
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