"كتيّب بلاد الرافدين. المجلد I. ١٩١٨" [‎٣‎٦] (٥٦٨/٤٥)

36
CLIMATE
The greatest ranges of temperature which may ordinarily be
anticipated, i. e. the difference between the mean monthly maximum
and mean monthly minimum temperatures, are 92-0° F., 90-9° F.,
and TG-S 0 F. for these three stations respectively.
Rainfall (Table IX, p. 50)
While the rainfall of lower Mesopotamia is less than that of
upper Mesopotamia, still an inch of rain usually falls in each
of three months of the year. At Baghdad and Babylon the largest
rainfall is in March, while at Basra the total for January is the
highest, being thus intermediate between the later date of the
maximum rainfall at places in northern Irak, and December, when
the heaviest rainfall at places in the Persian Gulf is recorded. The
total amount is not large at any station, ranging on the average
from 4 to 7 inches. June to September are practically rainless,
and in April, May, and October the amount which falls is small. The
rain days are consequently few (see Table X, p. 50), the highest
average number being 3-6 in March at Baghdad and in December
and January at Babylon, while at Basra it is 2-6 in January.
Snow falls occasionally, and as many as four days of snow were
recorded in January, 1912, at Babylon.
Humidity (Table VIII, p. 48)
The mean relative humidity at Baghdad lies between 60 and
80 per cent, from November to April, but falls much lower in
the summer, and is only 38 per cent, in June, from which it rises
slowly to 44 per cent, in September. At Babylon the values are
lower. Here, even in the winter, very low relative humidities
occur, 10 per cent, or less having been recorded in every month
except December and January during the period 1907-11.
Thunderstorms (Table XII, p. 54)
Thunderstorms appear to be rather frequent, for at Babylon,
which is the only place at which they have been regularly recorded,
they show a well-marked maximum in April and May, when nearly
five occur on an average. During the five years over which the
observations extended, 8 occurred in April of one year and 10 in
May of another. In July, August, and September none occurred,
and only a few in the autumn.