Case studies 

i) Rainfall variability. 
Winter crop rainfall in Queensland is highly variable compared to the rest of Australia. 
Queensland farmers use stored soil moisture from summer rains for their crops to 
supplement the erratic winter rainfall. 
At Dalby in southern Queensland, 150mm of in-crop rain (May 1st to October 1st) falls 
in only 60% of years. 
At Wagga Wagga in New South Wales and Merriden in Western Australia, 150mm or rainfall
is received in 90% of years. 

In other words, farmers in the Mediterranean climate of southern and western Australia
can almost always rely on sufficient in-crop rainfall to produce reasonable yields.
In Queensland, if the summer rains fail, the chance of harvesting a good crop the 
following winter is greatly reduced. 

(ii) Chickpeas and SOI. 
The chickpea growing season at Goondiwindi is May 1st to October 10th. 
From a water use efficiency model, we estimate 280mm of winter rain is needed to grow
a profitable chickpea crop. Interrogating HOWOFTEN? shows that the best probability (42%)
of achieving this rainfall occurs when the SOI is rapidly rising in April-May. The 
probability is zero if the trend is rapidly falling and under 30% in other years. 
Clearly the dice are loaded in favour of successfully growing chickpeas when the SOI is 
rising rapidly through April-May.