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October 14th 2010 print

Tom Quirk

BOM loses rainfall

Analysts at the Australian Bureau of Meteorology have some explaining to do. In the last two years some 900 mm of rainfall have been removed from the rainfall record of the Murray-Darling Basin.

Shock Murray-Darling Basin discovery 

Analysts at the Australian Bureau of Meteorology have some explaining to do. 

In the last two years some 900 mm of rainfall have been removed from the rainfall record of the Murray-Darling Basin. This startling discovery was made by comparing the annual Murray-Darling Basin rainfall reported on the Bureau of Meteorology website in August 2008 and the same report found yesterday. 

The annual rainfall figures are shown as reported in October 2010: 
Yearly rainfall in the Murray-Darling Basin from 1900 to 2009 as reported in October 2010 with a mean value of 467 mm (solid line).  

There is no significant trend in rainfall through this period but there is large variability with rainfall extremes of a 257 mm minimum and a 787 mm maximum. 

The comparison with the August 2008 report is revealing. The difference is a decrease of 900 mm rainfall in the 2010 report. The significant decrease occurs after 1948: 
Changes to Bureau of Meteorology record of Murray-Darling Basin rainfall. Data downloaded August 2008 and October 2010 

The Bureau is already on record adjusting Australian temperature measurements and they now appear to have turned to rainfall, making the last 60 years drier than previously reported. 

One can understand that adjustments might be made to a few of the most recent years as records are brought up to date but a delay of forty or fifty years seems a little long. 

This raises the question how certain is the data that is used by policy makers? 

When we are confronted by apparently definitive forecasts of our future with rising temperatures and less rain, are we living through a period that brings to mind the Polish radio announcement of Soviet times?: 

The future is certain only the past is unpredictable.

 

UPDATE: Read Tom Quirk’s postscript to this article here