On clear nights in the late autumn and winter a very heavy dew falls, quite sufficient to saturate any bedding or kit left exposed to it.
On the west side of the watershed little or no dew falls.
To the west of the hills the rainy season coincides with that in the Nile Valley, while in the east rain may be expected between November and March, although local thunderstorms may occur at other times of the year.
The winter rain in the western hills is sometimes heavy thunder rain, and at other times a heavy downpour or thick mist, unaccompanied by electrical disturbances.
Vegetation.In the lower parts of the khors, where they merge into open desert, the vegetation is very scanty. It is confined to a thin line of scattered scrub which marks the lowest part of the valley.
As the valleys become narrower and more marked the trees are larger.
Selem, samr, and tundub, form the chief part of the vegetation, with gamob in Wadi Amur and a thick belt of “eitil” in Khor Arab, near its junction with Khor Oi.
In the valleys east of the watershed the trees are larger and more numerous. Khor Adit is especially noticeable in this respect, with its large gemmeiza trees near Sinkat well, its thick covering of arak bush along the bed of the valley, and sunt and other trees of considerable size near the watercourse. The steep and stony khors, however, such as Khor Garar and the upper part of Khor Okwat, are in most places swept too bare of earth to allow of the growth of trees of any size.
The grazing on both sides of the watershed is confined to the actual valleys.
The watersheds dividing the westward-flowing khors are low rough ridges of black rock and gravel, and are practically destitute of vegetation.