ARID PORTIONS OF SOUTH AUSTRALIA. 55 



CLIMATE. 



Rainfall. 



The most arid part of South Australia, as well as of Australia as a 

 whole, is situated in the Lake Eyre Basin, as has already been pointed 

 out. The character of the rainfall for Oodnadatta may be taken as 

 representative of other portions of this intensely dry region. Ap- 

 parently the station with the least average rainfall is Kanowana, 

 where it is 4.33 inches annually; at Oodnadatta, however, the average 

 is 4.85 inches. The monthly average distribution of the rainfall at 

 Oodnadatta is given in table 12, which shows that the seasonal raina 

 are fairly equally divided, although averaging highest in the summer. 

 Thus, at Oodnadatta the average is 1.80 inches in summer, 0.98 inch 

 in autumn, 1.03 inches in winter, and 1.04 inches in spring. As table 

 12 suggests, the actual rainfall month by month for different years is 

 very unequal in amount, so that a table of averages does not have the 

 significance it otherwise might possess. The seasonal periodicity, so 

 well marked over much of the state, is accordingly not so dependable 

 at Oodnadatta and in the Lake Eyre Basin. However, as has just 

 been indicated, the rains of summer, undependable as they may be 

 and slight as they are, are nevertheless rather more in amount than 

 those of any of the other seasons; and it is not impossible that the 

 adjustment of certain of the native plants to their environment is 

 sufficiently delicate so as to largely hinge on just such relatively small 

 differences in the seasonal rainfall. So far as the character of the 

 individual storms is concerned, relatively few of them are of so large 

 amount as to be mainly lost by superficial run-off. On the other 

 hand, a remarkably large percentage of the rainfall occurs in amounts 

 too small to directly benefit plants. The proportion of the total 

 rainfall which occurs in separate storms, amounting to 0.15 inch or 

 less at Oodnadatta, lies between about 17 and 56 per cent of that for 

 the year, as shown by the rainfall records of 1901-1906, inclusive 

 (table 11). The average monthly effective rainfall for those years is 

 as follows: January 0.06, February 0.64, March 0.03, April 0.32, May 

 0.24, June 0.29, July 0.34, August, 0.13, September 0.46, October 

 0.15, November 0.29, and December 0.20 inch. According to these 

 records, therefore, the storms of summer, so far as the effective rainfall 

 is concerned, are considerably less than those of winter. Inasmuch 

 as the actual summer rainfall exceeds that of winter, it would be of 

 much interest and importance to know, when a long series of years is 

 taken into account, whether over such long period the effective rain- 

 fall would hold the relation above shown to be the case during the 

 years 1901-1906, inclusive. 



