CLIMATE OF ALGERIA. II 



this important climatic factor for the colony as a whole. Thus the annual 

 evaporation-rainfall ratios are as follows: the littoral, 2.5; the Tell, 3.5; 

 the High Plateau, 9.4; the desert, 46.5. The relation of these expressions 

 may also be given thus: 1:1.4:3.7:18.6, for the several regions above 

 given, by which we see how rapidly the aridity of the country increases as 

 the desert is entered. The present custom of considering the southern 

 base of the Sahara Atlas as the northern edge of the desert, in place of 

 including the High Plateau, as was done earlier, is thus well grounded. 



The temperatures of the air vary greatly for the different regions, and 

 usually the variation is to be directly related to the positions of the stations 

 as regards the coast and the altitude. Along the coast, however, the tem- 

 peratures vary even if the stations are at approximately the same eleva- 

 tion. The mean annual temperature at Oran is 16. o° C. and at La Calle 

 1 7. 7 C, while a study of the January temperatures shows that a similar 

 relation holds good for the entire south coast of the Mediterranean, be- 

 tween Oran and Alexandria. Algiers furnishes one exception to this state- 

 ment, in that the mean annual temperature is 18. i° C. On the High 

 Plateau the mean temperature falls to 12.7 C. (Batna) and 13.5 (Setif). 

 No records appear to have been made for the high mountains of eastern 

 Algeria, although the fact that snow may remain in sheltered places as 

 late as the latter part of July* would indicate that the mean temperature 

 at 2,000 meters elevation is much lower than any above given. On the 

 Algerian Sahara the mean annual temperature is usually higher than at 

 any point nearer the coast, but even here there is considerable variation, 

 depending, among other factors, on the altitude of the stations and their 

 relation to the Atlas. The mean temperature is given by Engler as 20.5 C. 

 for Biskra, 21.0 C. for Ghardaia, and 2 2. 2 ° C. for El Golea. As increased 

 temperature means increased evaporation, we have in this one factor a pow- 

 erful agent making for aridity, and when this is associated with decreasing 

 rainfall, as one leaves the coast region, its influence as a determinative fac- 

 tor in the environment of plants is thus seen to be of great importance. 



The annual variations in the temperature of the air are very consider- 

 able throughout the colony and are especially great on the desert and 

 the High Plateau. At Algiers the variation is 40. 7 ° C, at Setif it is 

 48. 2 C, and at Ghardaia it is 47. q° C. An annual absolute variation 

 of 50 C. is not uncommon on the desert, and Engler cites a range of 

 57.0 C. at Ghardaia. 



The daily range of the temperature is also considerable for all stations, 

 but is especially marked in those of the High Plateau and the desert. The 

 daily range as given by Engler for the former is 17.4 C., and for the latter 

 20.0 C, but the range on the High Plateau may be greater than 17. 4 C, 

 especially during the summer months. For example, at Batna, in 1904, a 



* Kearney and Means, loc. cit. 



