IRRIGATION. 



29 



Tablk 5. — Rainfall (in iiiclics) of loralitirs in tlw deserf region of Algeria, as compared 

 with si))til<ir localities of the soiUhii'eMerji United States. 



I 



Month. 



,lniiii!iry. .. 

 Februarv . 

 Mtucli ."..- 



April 



May 



June 



July 



August 



September 

 October . . . 

 November 

 December. 



Year 



Algeria. 



Tougoun, 



0.61 

 .54 

 .80 

 .44 

 .39 

 .04 

 .03 

 .02 

 .31 

 .43 

 .54 

 .88 



5.01 



Biskra. 



0.67 

 .68 

 .69 

 .83 

 .72 

 .31 

 .12 

 .14 

 .80 

 .59 

 .42 

 .74 



6.73 



Ouargla. 



0. .50 

 .30 

 .88 

 .36 

 .13 

 .11 

 .00 

 .00 

 .00 

 .22 

 .50 

 .6H 



3.61 



Bou 

 Saada. 



0.79 



.79 



1.32 



1.56 



1.55 



.67 



.32 



.31 



.91 



.87 



.64 



.88 



10.61 



United States. 



Yuma, 

 Ariz. 



0.48 

 .41 

 .27 

 .08 

 .03 

 .00 

 .13 

 .33 

 .15 

 .23 

 .26 

 .46 



2.83 



Phoenix, 

 Ariz. 



0.80 

 .70 

 ..58 

 .30 

 .13 

 10 

 03 

 88 

 64 

 37 

 54 

 86 



1 



6.93 



Tucson, 

 Ariz. 



0.79 



.90 



.77 



.27 



.14 



.26 



2.40 



2.60 



1.16 



.64 



.81 



1.00 



11.74 



Volcano 



Springs, 



Cal. 



0.25 

 .39 

 .07 



Trace. 



Trace. 

 .00 

 .12 

 .09 

 .00 

 .12 

 .07 

 .52 



1.64 



i 



I 



A comparison of precipitation in the Algerian desert and that of the 

 southwestern ITnited States is instructive antl interesting-. Bou Saada 

 has approximately the same annual total as Tucson, which it resembles 

 in situation and elevation, but there is the .same difference in distribu- 

 tion as was noted in the case of atmospheric humidity. More rain 

 falls in winter and less in summer at the Algerian than at the Arizona 

 locality. At Biskra and Phoenix very nearly the .same total amount 

 of rain falls during the year, and the disti"ibiition at the two points 

 corresponds more closely than as between Bou Saada and Tucson; At 

 Ouargla and at Tougourt the rainfall is considerabh' greater in yearly 

 total tlian at Yuma and at Volcano Springs. In distribution, however, 

 these four stations resemble each other to a considerable degree. On 

 the whole, if we consider only localities which repre.sent the mo.st 

 extreme conditions in both great arid regions, it would appear that the 

 desert country of the southwe.stern United States is decidedly drier 

 than the Sahara of Algeria. 



IRRIGATION. 



Algeria i.s less fortunately endowed than Egypt as regards water 

 supply. She has no large river like the Nile, containing even at its 

 lowest stage a very considerable volume of water for irrigating pur- 

 poses. On the contrai\v, the water courses of the French colony are 

 of a torrential character, running high after lieav}' rains but dwin- 

 dling to mere rivulets in summer. Most of them are short, rising in 

 the mountain ranges of the coast region, and thus not draining a suf- 

 ficiently large area to gather a great volume of water. Their fall is 

 heavy, and they accomplish a vast amount of erosion, so that when 

 high their waters carry a large amount of silt. P^ven the Cheliti', 

 which has its source in the mountains that form the northern boundar}' 

 of the Sahara and traverses the entire width of the high plateau, is 



