Fifth article in a series that discusses the technical aspects of rainfall
While, from various aspects, all and any rainfall measured against the background of an arid climate will provide some value, the rain measure bringing the grass lands, in particular to life and maintaining that life and its growth, carries considerable weight in our arid climate context.

It is that 8 mm minimal measure that provides the starting point. Preferably, bearing in mind our scales of temperature, both in the air and on the surface, a 10mm measure provides a more secure base from which to identify a productive fall of rain. Grass growth should be expected following such a measure and further similar falls should maintain that growth across the following days stretching into weeks.
Depending on the porosity of the soil, the growth will ensue across a varying number of days.
The point has been raised concerning, say, two consecutive days of , again say, 8 or so mm. Would there not be sufficient penetrative volume to ensure or maintain grass growth? I feel that that decision can only be made where individual instances can be regularly noted. It would depend purely upon the soil types at that particular place, such considerations are beyond the immediate world of rainfall. Further, what about 9.9 or 9.8mm falls? Mr Ben Strohbach commented “Don't split hairs”. Again, such splitting of hairs could only be done against the much localized background of one particular site.
We have not got down to the task of plotting rainfall, on the current day-to-day basis, on to a local or regional map, to provide indicators of grass growth potential.
First of all, the current rainfall stations do not make daily reports. Their monthly return is the requirement of an official rainfall station; secondly, telephonic reports are notorious for their potential for inaccuracy, no matter how dedicated the observer or the recipient may be. The verification of that monthly return provides valid fulfillment.
A further consideration is that the reporting station is but a dot on the map. Unless a broader range of data is available, one must assume that there is a very limited range to that individual value as measured. One does not have to be an ardent weather observer or rainfall reporter to know how desperately limited is the range of an individual shower or thunderstorm.