CLIMATE. 13 



CLIMATE. - 



Exact data in regard to the climate of the Oiied Souf are not easily 

 obtainable. The observations here given were made chiefly by a 

 medical officer of the French army during the summer of 1884."' 

 Unfortunately records covering a period of several years are not 

 available.'' 



The summer temperatures are very high, few hotter localities being 

 known in the Sahara. The monthly maximum shade temperatures 

 observed by Escard in the summer of 1881 are as follow^s (in degrees 

 Fahrenheit) : 



April 93 



May ____•___ 100 



June 10(3 



July 122 



August 116.5 



September 113 



October 91. 5 



In June, 1901, a maximum of 127.5° F. is said to have been reached. 

 The sum total of temperature during the summer, a factor of the 

 greatest importance in the ripening of the finer varieties of dates, is 

 said to be greater in the Oued Souf than in the Oued Rirh and the 

 Djerid. At the time of the writer's visit (November 22-26, 1901) 

 cool, cloudy weather prevailed, and the nights were decidedly cold. 



o Escard. Etude medicale et climatologique sur le pays de I'Oued Souf. 

 Archives de Med. et de Pharm. Milit, 7 : .33 (18SG). 



6 Since the above chapter on climate was written the records of observations 

 made at El Oued during the whole of 1904 and parts of 1903 and 190.") have been 

 received, through the courtesy of the Director of the Meteorological Service of 

 Algeria. These observations necessitate some modifications in the previously 

 written discussion of the climate of the Souf. The absolute maximum tempera- 

 .ture at El Oued in 1904 was 121.8° F. in May instead of 127.5° F. in June. The 

 absolute minimum in 1904 was 32° F. The mean relative humidity during 1904 

 at El Oued was 58.8. which is lower than the normal at Tozer, in Tunis (G0.8), 

 but higher than the normal at Ouargla and Biskra, Algeria (47.2 and 48.4, re- 

 spectively), and at Yuma, Ariz. (42.9). The sum of the monthly means of 

 evaporation at El Oued in 1904 is 1.50 inches, while the normal at Tuzer is 94 to 

 98.5 inches. The total precipitation at El Oued in 1904 was 3.23 inches, while 

 the normal yearly total is 3.61 inches at Ouargla, 6.73 inches at Biskra, 5.1 

 inches at Tozer, and 2.83 inches at Yuma. 



The ol)servations on the prevailing direction of the wind during 1904 and the 

 first half of 1905 do not agree with those made by Escard and quoted in the 

 text, but the data are insutticient for an adequate discussion of this factor. 



As the climatic factor which is most important in date growing is probalily 

 the effective temperature during the ripening season, a calculation has been made 

 of the sum totals of daily mean and of daily maximum temperatures above 

 «^.4° F. (18° C.) during the months of May to October, 1904, at El Oued, and. 

 for the sake of comparison, of the sums for the same months of the same year 

 at Ouargla and Biskra, Algeria; Tozer, in Tunis, and Mecca, in the Salton 

 Basin. California. Records at Mecca for May and June. 1904. not being avail- 

 able, the records for those months at Imperial, Cal., were substituted in making 



