traditional region, east-central Sudan. It is bordered on the east by Ethiopia. The Atbara River, an important tributary of the Nile, flows northwestward through Kassala and causes seasonal floods during torrential summer rains. Rocky deserts dominate the centre of the region, while in the north is the Butana Plain, with sandy clay soils and occasional low hills with short grass scrub and acacia. The south is underlain by Nubian sandstone and has thickets of acacia trees and tall grasses. Rainfall decreases steadily from south to north, with 40 inches (1,000 mm) falling annually in the extreme south but only 13 inches (330 mm) at Kassala town. The chief settlements in the region are Kassala and Al-Qadarif.
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