Rain Producing Influences in South Australia. 103 



miniiniim temperature departtires so often show, a wide flow of 

 air coming inland from the neighborhood of Wyndham or Port 

 Darwin, this may carry its water vapour without much addition 

 from the dry plains beneath for perhaps 2000 miles before it 

 shows by its cloud production that through gradual cooling 

 the limit of its moisture-holding capacity is nearly reached. 

 Precipitation may not begin till the Murray is reached, or even 

 the highlands of the Divide, but it might begin considerably 

 earlier, and perhaps two or three hundred miles further inland if 

 it encountered the disturbing effect of buoyant, moist air rising 

 from such a source as L. Eyre or L. Torrens. That is, for 

 large inland areas, the influence of the lake evaporation helps 

 to determine not only the amount of rain, but perhaps more often 

 whether there shall be some rain or none. In a sense it may be 

 partly a question as to when and where ''the tap is to be turned 

 on." 



Australia's Increasing Aridity — a Partial Cause. 



In these papers, reference has already been made to 

 the different ways in which vegetation may affect rain- 

 fall. It has flrst been shown that the substitution of growing 

 cereal crops or grass for Mallee scrub causes a marked increase 

 in the rainfall of the districts in lee of the improved area, 

 especially in spring. Then irrigation was proved to show some 

 similar effects. And now I have been able to show greater 

 effects still, from the recently increased water storages in the 

 great lakes of South Australia, the benefits being almost on a 

 continental scale. For the increasing lake water storage, the 

 changing character of the natural drainage channels, and the 

 lessening of the water demands of the forest covering under 

 pastoral occupation have been shown to be important factors. 

 We may now logically apply these results to the solution of a 

 larger problem. 



The early settlers in the eastern interior of this continent 

 found inland perennial vegetation to consist first of a belt of 

 vigorous growing trees with abundant foliage occupying the 

 more elevated upland regions; next on the foothills and adjacent 

 plains the hardier types of the same with smaller leaf surface; 

 then further inland stunted and distinctly drought-resistant 

 types, such as Mallee eucalypts, bull-oaks (casuarinas), etc. ; and 

 further inland still, under severer conditions, salt bush, blue 

 bush, etc. 



