This tectonic environment sets the stage for the
hydrology of Iraq which is at least partly related
to the major dust storms that we are seeing in the
news. The trough of the overall syncline of Iraq
is occupied by the twin rivers, the Tigris and
Euphrates, the lower reaches of which gave birth
to some of the earliest civilizations. These
rivers (along with some smaller rivers)
historically fed the Mesopotamian marshlands which
used to occupy the plain which dominates much of
south-eastern Iraq. In the last decade or few,
major hydro-engineering structures have held back
this water in reservoirs, diverted it for
irrigation, or simply re-routed it so that it
wouldn't supply the marshlands and, as a result,
about 90% of the marshlands have become dry. Fine
sediments tend to settle out of stream water when
it slows in marsh or lake systems so the soil
exposed by drying the marshes is composed of
readily erodible fine particles. Add strong winds
(which I'll talk about in a moment) and a lot of
vehicles driving over these surfaces, and you get
a lot of fine material getting into the atmosphere
and making very severe dust storms.
During spring and autumn months,
atmospheric low pressure systems can develop over
Iraq which bring with them the Sharqi, a gusty and
dusty wind from the southeast that comes with
serious dust storms and sometimes thunderstorms.
As temperatures warm during the summer, a high
pressure system develops and the winds (called the
Shamal) become more steady from the north and
northwest and are very dry.
shows this reasonably well.
satellite images of the dust storms we've heard
about in the region of late,
This shows the Sharqi and that these winds
can carry dust from as far away as Africa.
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