A fair statement about the NSW trend from 1900 could be that after abnormally wet years from the end of the 1940's to the 1970's we have returned to a more normal rainfall pattern similar to the 1900 to 1945 period.
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It just so happens that 1950 was
the standout highest year in the NSW
rainfall record, at 930.15 on the Bureau of Meteorology (BoM) web site,
see the BoM graphic. So to use that year as a starting point of
course
a decline will be shown, which is very misleading unless policymakers
are also well aware of the statistical implications of the full
dataset, that choosing slightly different starting points can give very
variable results. A fair statement about the NSW trend from 1900 could be that after abnormally wet years from the end of the 1940's to the 1970's we have returned to a more normal rainfall pattern similar to the 1900 to 1945 period. |
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From the late 1940's to 1974
there were 6000 aircraft hours of cloud
seeding experiments carried out over SE Australia. The graphic
below
maps the rainfall anomaly for those years. So it is possibly that the much maligned cloud seeding experiments contributed to the high rainfall year of 1950 which CSIRO then use in a misleading way to convince the NSW Govt that future rain prospects are grim. You could hardly write a better black comedy plot. This map comes from a 2002 report by Ian Searle submitted to "The House of Representatives Standing Committee on Agriculture, Fisheries and Forestry Inquiry into Future Water Supplies for Australia’s Rural Industries and Communities." I can email a copy if you can not find using Google. |
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This graphic demonstrates how much of Sydney rainfall comes in relatively few scattered high rainfall months. Rainfall which has now been characterized as "freak" by Tim Flannery. Wonderful, a century long repeated natural phenomenon now is "freak". |