I do not measure it but it is so in ...
When someone asks you about how you are measuring something and you didn't personally do the measuring, then just read that is "what measure are you using?" ... in this case, that would be: "something to do with rainfall". Which is not very specific. In order to help you, I need to know about how you are thinking.
Are you thinking annual rainfall or record low rainfall?
How do you decide on a rainfall figure for an entire continent?
Are you counting snow or just liquid water?
But at least it's more specific than "driest"
...it is so in the informations I found.
Where did you find those "informations"? What sort of data sources are you using?
Precipitation data is quite easy to find - but tends to be "rainfall equivalents" for Antarctica.
The various scientific bases there keep track while the Australian government has a whole met service to look up ;)
A brief informal scan suggests 5-600mm/annum for Oz, and 1-200mm/annum for Antarctica... what data you use depends heavily on what you want it for.
Driary must be related raining amount.
Note: do you have a link to a dictionary definition for the word "driary"?