"كتيّب الجزيرة العربية المُعد تحت إشراف القسم التاريخي لوزارة الخارجية – رقم ٩٠". [‎٧] (١٤٨/٢٢)

Arabia]
CLIMATE
7
The western side of the Yemen plateau drains to
wards the Red Sea through several wadis, while others
flow eastwards and lose themselves in the sand. In
Asir, too, are numerous fertile valleys, the largest, the
Wadi Bis,ha, with its tributary thle Wadi Shahran
being in the east. The most important wadi in Hejaz
is the Wadi Hamd, which unites two main channels
from the ridge, one draining the Kheibar Harra, the
other the Aweirid Harra. The first gives Medina its
underground water and extensive oasis; the second
supplies the palm-groves of El-Ala.. Generally, how
ever, the wadis of Hejaz produce very little fertility,
and in the northern part of the district (Midian)
practically none.
(3) Climate
The climate of Arabia, thanks to its extreme dryness,
is generally healthy and invigorating. Travellers in
the desert or mountains often suffer more from cold
than from heat, and snow is not infrequent in the
highlands of the north. In the interior the nights are
cool, even in the hottest months, and on the highest
plateaux the daily range of temperature is enormous.
On the coast, however, the heat is usually oppressive,
Jedda, Hodeida, and Muscat being among the hottest
towns in the world.
Like Persia and Egypt, Arabia is exceptionally dry
and rainless, and only in Yemen and Asir are there
sufficient periodic rains for cultivation. For the rest,
the most favoured region is the northern Nefud with
Jebel Shammar, but the rainfall here is less than that
of the Egyptian Delta. Over the rest of the central
mass and the greater part of the southern desert the
rainfall is almost entirely absent.
The Midian highlands get rather more rain than the
Egyptian Delta, and the rest of the Hejaz rather more
than Middle Egypt. In Mecca and Medina, as well
as further north, heavy rains occur during thunder
storms. In the Hejaz lowland the mean annual