'IRAQ AND THE PERSIAN GULF' [‎129r] (262/862)

CLIMATE
I ?7
snowfall in a year. 1 In winter every year snow falls on the Kurdish
and Persian hills, and in the higher parts foul weather with snow may
last a fortnight or longer. One traveller at the end of January records
continuous snow-cover on northward-facing slopes down to 3,500
feet, and deep snow on sheltered plateaux at 5,000 feet (photo. 71).
Southern aspects at this altitude would clear after two days’ sunshine,
but passes are often blocked to animal transport. January and
February are apparently the months of greatest snowfall in the
higher mountains. Movement in March and early April is much
impeded by flooded rivers caused by the melting snow.
Thunder is more marked from March to June than in other months
and is commoner in the north than in the south (fig. 47). It is a rare
occurrence after the coming of the Shamal until November. It is
sometimes heard without rain being precipitated, but rain from
April to June is generally accompanied by thunder, and occasionally
such storms are violent.
Hail is both a winter and spring phenomenon. It is not common,
but occasionally the stones are remarkable for their size.
Dust-storms (fig. 48; Table VIII)
The desert nature of Iraq favours the occurrence of dust-storms
because the alluvium is easily broken up by aridity and a hot sun
into fine particles of dust. A dust-storm is defined by two criteria, a
wind-force of 4 (Beaufort scale) or more and a decrease of visibility
to less than 1,100 yards caused by fine dust. The true sand-storm
(haboob) of the Sudan is very rare in Iraq, but dust-storms are
common and sometimes violent. In very severe dust-storms visi
bility may be reduced to 20 yards (photo. 72).
Dust-storms may occur at any time of the year, but they are
classified seasonally into two types: winter dust-storms from
November to May and summer dust-storms from June to October.
Winter storms are generally associated with the westerly atmospheric
depressions (p. 169) or with thunder-storms. If the ground has
dried sufficiently after the previous depression, dust may rise over
a wide area in front of the oncoming depression as the wind freshens
from the south-east. Thus many winter dust-storms come frequently
from this quarter. Others caused by thunder-storms are much more
1 The figures in Table VI for snow, thunder, and hail are taken from the Statistical
Abstract 1940 published by the Ministry of Economics in Iraq. The number of
years of observations is not stated.
A 5195
N