6 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



strictly speaking, be reg, but a wide-stretching bajada, and the soil is 

 probably only in small part deposited by rivers. 



CLIMATE OF ALGERIA. 



The climate of Algeria is mild and temperate. This is due to several 

 factors, among which are its situation relative to the Mediterranean on 

 the north and to the Atlantic on the west, as well as to the great desert 

 which constitutes its southern portion, the great variation in topography, 

 and the fairly low latitude. Taking the colony as a whole, there is a great 

 range in temperature, precipitation, relative humidity, and evaporation, 

 to mention only such climatic features as have been reduced and are re- 

 corded; and the range in the intensity and in the quality of the light must 

 also be great. The climate of the northern portion of Algeria is coastal, 

 while that of the southern portion is continental. 



The distribution in time and in space and the amount of precipitation 

 are of the greatest importance as climatic features of Algeria. The rain- 

 fall is heaviest on the littoral, and especially heavy in the eastern portion 

 of the littoral. An average of 1,000 mm. is reported from the immediate 

 vicinity of the sea,* and as one goes southward the amount of precipita- 

 tion rapidly becomes less. In the Tell the average rainfall is 570 mm., 

 while on the High Plateau it is 310 mm. On the desert the rainfall is un- 

 certain both in amount and in time, except that when rains occur the time 

 coincides with the rainy season of northern Algeria. At Biskra the annual 

 precipitation is 199 mm., at Laghouat it is 198 mm., at Ghardaia it is 114 

 mm., and at El Golea it is 47 mm. In many places in the western Sahara, 

 five years or more go by without fall of rain. 



The differences in the geographical distribution of precipitation vary 

 from year to year, as may be illustrated by referring to that for the year 

 1908, which may be compared with the normal usual distribution as given 

 above. In the northern portion of the country more rain than usual was 

 reported; for example, there was over 1,000 mm. on the littoral east of 

 Algiers, and over 500 mm. on the High Plateau, but on the desert the 

 amount was somewhat less. At Laghouat it was 161 mm., at Ghardaia it 

 was 89.2 mm., and at Ouargla it was 28 mm. 



Besides the differences in amount of yearly rainfall, well-marked seasonal 

 amounts of precipitation are also to be noted. In the northern portion of 

 the colony rains are likely to occur in winter and spring, the summer and 

 early autumn being dry ; and as one goes south of the Saharan Atlas nearly 

 the same conditions obtain; that is, the rains usually fall during the rainy 

 season of the coast. The seasonal distribution of rain for the Tell, includ- 

 ing the stations of the littoral, the High Plateau, the Saharan Atlas, and 

 the desert, for a series of years including 1908, is given in table 1. 



* A. Engler, Die Vegetation der Erde IX. Die Pflanzenwelt Afrikas. 1 Bd., 1910, 

 page 902. 



