'IRAQ AND THE PERSIAN GULF' [‎128r] (260/862)

CLIMATE I75
very small and conditions favourable to heat-stroke occur. For the
medical aspects of heat-stroke, see Chapter IX, p. 428-30.
Up country beyond the lower delta the relative humidity in summer
is lower, particularly in the early morning. The difference in comfort
is much more marked than appears from the mean figures. This is
caused in part by the fact that the Shamal is stronger and more regu
lar, and partly by there being less standing water. Everywhere the
Shamal brings relief, because it prevents stagnation of the air and so
increases evaporation from the body. Under canvas some relief can
be obtained by opening the lower parts of the tent in order to obtain a
draught of hot dry air.
Precipitation (fig. 46; Tables V, VI, VII)
Rain. Almost the whole rainfall of Iraq occurs in winter or spring
and accompanies the depressions crossing the country from the
Mediterranean. Of the five stations of which there are continuous
records for any length of time, Mosul alone has more than 6 inches,
and all indicate how arid are the plains throughout the six summer
months (Table V). December, January, and February are the wettest
months, but except in the north the mean of each of these three
months nowhere reaches 2 inches.
During the last few years the rainfall has been recorded at
a number of places by observers in different government depart
ments (Iraq Railways, Posts and Telegraphs, Police, &c.), and by
the Iraq Petroleum Company. From these (Table VI) it is possible
to construct a provisional rainfall map (fig. 46). Precipitation in
the Kurdish mountains is considerably higher than in the plains,
Zakho, Amadia, Ruwandiz, and Halabja all recording an average of
more than 40 inches for the 4 years from 1936 to 1939. Travellers
in the mountains write of rain falling on every day for two or three
weeks on end in winter. This higher rainfall causes the sudden
rises in volume of all the left-bank tributaries of the Tigris which
are so marked a feature of their regimes (p. 26).
The normal number of wet days is not high even in winter, so that
rain when it comes is fairly heavy. But the two days which have
recorded the heaviest downpours both fell outside the three normally
wettest months: 4*5 inches in 24 hours at Diwaniya in May and
3*4 inches in 24 hours at Mosul in November.
Snow. Snow and sleet have occurred throughout Iraq at different
times, but none of the four stations average more than two days’