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to fail. The catchment basin of the Gazelle river may be credited with 
a mean annual rainfall of 7 5 centimetres between May and October, 
while the mean annual rainfall on the Arab river cannot be more 
than 30 centimetres between June and September. The Sobat river 
in its upper reaches enjoys an annual rainfall of about 1.25 metres 
and of *75 metres in its lower reaches. The time of rain is between 
March and September. The lands draining into the White Nile north 
of Tewfikieh have an annual rainfall of about 20 centimetres between 
June and September. 
The Abyssinian part of the catchment basin of the Blue Nile enjoys 
a good rainfall throughout nine months of the year from February 
to October, with generally heavy rain between May and September, 
and very occasionally in October. The rainfall here may be taken as 
1.25 metres per annum. In the plains of the eastern Sudan traversed 
by the lower reaches of the Blue Nile and the Atbara the rainfall is 
very much lighter and may be considered as 30 centimetres between 
July and September ; fairly constant and heavier in the south, and very 
inconstant and lighter in the north. The Atbara and its tributaries 
in their upper reaches on the northern slopes of Abyssinia, have rain 
from May to the end of August and occasionally into September. 
There are great fluctuations in the rainfall. The mean annual rainfall 
may be taken as 75 centimetres. 
The desert area between Khartoum and Cairo has occasional winter 
rains especially in the parts near the Bed sea, but as these rains are 
nearly all soaked up by the desert, and very little, here and there, 
reaches the Nile, we may neglect them altogether. Railways have to 
be provided with culverts and bridges where they cross the terminal 
reaches of the khors and wadis which run considerable bodies of 
water for a few hours after rain; but the effect on the Nile is practi- 
cally nothing. Along the sea-board of the Mediterranean there are 
a few inches of rain every winter, sufficient as a rule to raise poor 
crops of barley. 
In the catchment basins of Lakes Victoria and Albert the direction 
of the winds may be taken as north-east in winter and south-east 
in summer. The maximum monthly temperature may be taken as 
35° and the minimum as 12°, with a mean for the year of 21°. 
Along the Albert Nile the north wind blows through the winter* 
and southerly winds prevail from about' the 15th of April to October 
The temperature may be taken as ranging from a monthly maximum 
of 38° to a monthly minimum of 16°, with a mean of 27°. 
