14 



PLANT HABITS AND HABITATS IN THE 



Fig. 56. — Mean rainfall of Australia for October, after Hunt. 



Evaporation. 



A relatively high rate of evaporation is one of the most striking 

 features of the Australian climate taken as a whole (table 4 and fig. 8a). 

 In a large portion of the continent it exceeds the rainfall, and in certain 

 regions, as indicated by table 3, the difference between evaporation and 

 rainfall may be very great. Moreover, in a fairly large area the annual 

 evaporation is relatively and actually high. Thus in about 40 per cent 

 of the continent the total evaporation is 100 inches or more annually. 

 Since there is a direct relation between the rate of evaporation and the 

 temperature of the air, as well as with other climatic factors, such as 

 relative humidity and rainfall, it follows that there is a regular course 

 run by it during the year. This feature is shown in figure 6. It will be 

 observed that in regions of winter rainfall the course of the monthly 

 evaporation amount is fairly consistently opposed to that of the rain- 

 fall, but that in regions within the zone of summer rains, as at Brisbane, 

 there is more or less coincidence between the course of the two climatic 

 elements. Table 4 is a detailed summary of the mean monthly and 

 annual evaporation amounts, as well as the highest and the lowest 

 means, for 4 stations. 



