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Roughly 90 percent of the annual rainfall occurs between
November and April, most of it in the winter months from December
through March. The remaining six months, particularly the hottest
ones of June, July, and August, are dry.
Except in the north and northeast, mean annual rainfall
ranges between ten and seventeen centimeters. Data available from
stations in the foothills and steppes south and southwest of the
mountains suggest mean annual rainfall between thirty-two and
fifty-seven centimeters for that area. Rainfall in the mountains
is more abundant and may reach 100 centimeters a year in some
places, but the terrain precludes extensive cultivation.
Cultivation on nonirrigated land is limited essentially to the
mountain valleys, foothills, and steppes, which have thirty or
more centimeters of rainfall annually. Even in this zone,
however, only one crop a year can be grown, and shortages of rain
have often led to crop failures.
Mean minimum temperatures in the winter range from near
freezing (just before dawn) in the northern and northeastern
foothills and the western desert to 2o-3° C and 4o-5° C in
alluvial plains of southern Iraq. They rise to a mean maximum of
about 15.5° C in the western desert and the northeast, and
in the south. In the summer mean minimum temperatures range from
about 22.2° C to about 29° C and rise to maximums between
37.7o and 43.3° C. Temperatures sometimes fall below freezing
have fallen as low as -14.4° C at Ar Rutbah in the western
They are more likely, however, to go over 46° C in the summer
months, and several stations have records of over 48° C.
The summer months are marked by two kinds of wind phenomena.
The southern and southeasterly sharqi, a dry, dusty wind
with occasional gusts of eighty kilometers an hour, occurs from
April to early June and again from late September through
November. It may last for a day at the beginning and end of the
season but for several days at other times. This wind is often
accompanied by violent duststorms that may rise to heights of
several thousand meters and close airports for brief periods.
From mid-June to mid-September the prevailing wind, called the
shamal, is from the north and northwest. It is a steady
wind, absent only occasionally during this period. The very dry
air brought by this shamal permits intensive sun heating
of the land surface, but the breeze has some cooling effect.
The combination of rain shortage and extreme heat makes much
of Iraq a desert. Because of very high rates of evaporation, soil
and plants rapidly lose the little moisture obtained from the
rain, and vegetation could not survive without extensive
irrigation. Some areas, however, although arid do have natural
vegetation in contrast to the desert. For example, in the Zagros
Mountains in northeastern Iraq there is permanent vegetation,
such as oak trees, and date palms are found in the south.
Data as of May 1988