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What was once the Aral Sea at Muinak,
Qoraqalpoghiston, Uzbekistan.
Photo: so11e via Flickr. |
The Aral Sea is a well known environmental disaster
zone. But this year, it got a whole worse, writes Anson Mackay, as its
biggest basin dried up completely to expose a toxic, salty wasteland.
With continuing irrigation and declining river flows due to climate
change, the desert is only set to expand.
The Aral Sea has reached a new low, literally and figuratively. New
satellite images from NASA show that, for the first time in its recorded history, its largest basin has completely dried up.
However, the Aral Sea has an interesting history - and as recently as
600-700 years ago it was as small, if not smaller, than today.
The Aral recovered from that setback to become the world's fourth largest lake, but things might not be so easy this time round.
Today, more people than ever rely on irrigation from rivers that
should instead flow into the sea, and the impact of irrigation is
compounded by another new factor: climate change.
Really a lake - but now, a wasteland
Sandwiched between Kazakhstan and Uzbekistan, the Aral Sea is
actually a lake, albeit a salty, 'terminal' one. It is salty because
evaporation of water from the lake surface is greater than the amount of
water being replenishing through rivers flowing in.
It is terminal because there is no outflowing river. This makes the
Aral Sea very sensitive to variations in its water balance caused either
by climate or by humans.
Indeed, the sea has long been a
cause celebre in the world
of environmental catastrophes, an exemplar of the devastating harm that
ill thought-out economic policies can have on the environment.
Intensive irrigation of cotton plantations in the deserts of the
western Soviet Union prevented water reaching the Aral Sea, leading to
the drastically low levels we see today. This in turn meant the
highly-salty waters
killed off many plants and animals.
During early Soviet Union times, the Aral Sea and its fringing
wetlands were a significant resource for the fishing industries,
agriculture, animal husbandry and fur trapping.
Six decades of profligate cotton irrigation
But in the 1950s, the extent of irrigated land used for 'white gold'
(cotton) increased dramatically from 4 billion to 8 billion hectares,
with Uzbekistan becoming one of the world's
largest cotton producers.
To feed cotton's insatiable demand for water, the Karakum Canal was
built out of the desert sands and because it was unlined, water losses
were extremely high.
During the late 1960s, the amount of water evaporating from the Aral
Sea become greater than the amount of water entering the lake, so lake
levels declined dramatically in the 1970s and 1980s. More than 75% of
the surface area and more than 90% of the lake's volume has been lost.
In 1987-1988, the lake split into two, and the Large and Small Aral
Sea basins were created. International efforts have been made to protect
the Small Aral Sea through the construction of dams, and this has meant
that lake levels here have
increased.
The Large Aral Sea continued to shrink and subsequently split itself
into two basins; a deeper, smaller west Large Aral and a more shallow,
but expansive, east Large Aral. And it is this latter basin which NASA
images show had dried out completely this summer.
Toxic, salty dust storms causing disease and death
The environmental impact of the drying Aral has been devastating.
Hundreds of thousands of people have been displaced and hundreds of
species have disappeared. Toxic metals and agrochemicals (herbicides,
pesticides, insecticides), used to prevent disease and pests from
lowering cotton yields, found their way into the sea through its rivers.
But because the Aral is a terminal lake, the pollutants were never washed out, and they instead sunk to the bottom sediments.
Now these bottom sediments are exposed to the air, they are blown up into the atmosphere as
toxic, salty dust storms, which can spread for many hundreds of kilometres causing increased deaths and chronic disease,
especially the young.
However, lower lake levels have also exposed ancient irrigation
systems and mausoleums surrounded by settlements (some remains of which
are still under water), built during the late Middle Ages. This means
that in certain parts of the Aral, lake levels during 13th-14th century
must have been lower.
We still aren't sure exactly what caused such extreme regression, but
a cooler, drier climate played a role. The 13th century Mongol invasion
of central Asia also led to the Amu Dar'ya, one of two major rivers
that feed the Aral, being
diverted to the Caspian Sea. Clearly humans were a major factor in the Aral's previous dry spell.
By the late 16th century, the Aral Sea started to fill up again, in
part because irrigated channels meant the Amu Dar'ya once more
flowed into the lake.
With climate change and continuing irrigation, water flows will cease
A key question that remains today therefore is how much of the lake's
current regression is due to intensive irrigation and how much may be
due to climate change over the past 50 years. Recent studies suggest
only 14% of the shrinking of the Aral Sea since the 1960s was caused by climate change, with irrigation by far the biggest culprit.
Researchers looking at what will happen to Aral Sea levels with
global warming over the next few decades have combined several model
predictions together and expect
net water loss to increase as more evaporation leads to less river inflow.
However, if irrigation of the rivers continues, then net water loss
will be even greater as river flow into the Aral Sea will essentially
cease.
Climate change may be one of the world's great problems but
over-irrigation is at least possible to reverse with the right policy
changes. But the two issues together make a disastrous combination.
The future for much of the Aral Sea does not look great.
Anson Mackay is Professor of Environmental
Change at University College London. He received funding from INTAS
between 2003-2005 to research water level change in the Aral Sea over
recent millennia.
This article was originally published on
The Conversation. Read the
original article.
