The principal wadis, from north to south, are Hasium, Di-ib, and Haieit.
The Wadi Hasium, after emerging from the hills of Abu Hodeid, skirts the Kajoj and Musa ranges, which it leaves some distance to the south, and flows through open country to the sea. It contains the wells of Kajoj and Shalatein.
The Wadi Di-ib, perhaps the most important wadi of the Eastern Atbai, rises in the Amarar country, probably as far south as the 20th parallel, and flows generally northwards. About 20 miles before it turns eastwards to traverse the open maritime plain, it opens out into a wide basin, a mile in breadth and 8 to 10 miles in length, containing a bed of rich alluvial soil. This basin forms the principal cultivable land in the Um Ali Bisharin country. It is the property of the Shantirab, but portions are allotted both to the Amrab and Belgab in good years. An important tributary on the left bank of the Di-ib is the Wadi Hufra, which, rising in the Amrab country in the hills to the north-east of Onib, joins it at the north end of the J. Elba range. It receives all the drainage from the hills of the southern Belgab country by the Wadis Is and Legia. At several places in its bed, the Arabs cultivate and obtain good crops of dura.
Wadi Haieit, in the southern Atbai, is also said to be cultivated.
The ranges of Elba and Asotriba are composed of red granite, whilst at the foot of the latter are small hills of very beautiful hornblende porphyrite.
Climate.The climate of the Atbai is probably the best in the Sudan. The air is of absolute purity, and the elevation, 1,500 to 3,000 feet above sea level, very considerably mitigates the shade temperature. The heat of the sun, however, is intensely fierce in warm weather, owing to the glare from the sand and rocks. During the summer, waves of superheated air are occasionally known, such as that which destroyed a convoy on the march from Korosko to Abu Hamed in 1897.
In winter, the cold is quite severe, and anyone proposing to travel there in December or January should make sure he has plenty of bedding and warm clothes.
Though it is essentially a very dry climate, dew falls at Deraheib on the west of the watershed in December, and a misty haze, which seems to be connected with moisture in the air, frequently covers the whole country. The climate of the littoral is, as may be supposed, much warmer than that of the interior.
Rainfall.The rain falls in violent local showers during the months of July and August, called the “Shuti” rains. In exceptional years, showers occur in May and June.
Many places go without rain for several years in succession, but during the above-mentioned months it is always risky to camp in the bed of a wadi, as a spate may come down, though no rain nor clouds have been visible to the traveller.