Perth and Catchments Rainfall History and Water Resources

**Perth and Catchments Rainfall History and Water Resources**
On 15 April The West Australian ran front page headline, "Perth faces another dry winter disaster" Click for 1 September dam storage graphic from Water Corporation showing dams starting to take inflow early this year and inflows increasing after a wet August. Dams Tim Flannery statement The West Australian 25 June that "...Perth will die..." gets me to start a press page. Click on Dr. Tim. I can cope with a politician, the WA Premier making para-normal statements about water resources ("..we are in a 25 year drought...") but for a scientist to swallow CSIRO climate modelling as though it is written on tablets of stone, has me puzzled. Could it be the Federal election due soon ? Could this talk scare a few more waverers into voting Green ? Any comments welcome. Up to date prediction for just above average SW WA rainfall in May-June-July 2004 from modeling by Scripps Institution of Oceanography. Click to see global prediction.These pages have been posted by Warwick Hughes a free lance earth scientist who thinks there is room for more scientifically based input into the debate over the future of Perth's water supply. Comments can be emailed to wazzau2002@yahoo.com.au Updated April 2004 Drought in Australia web site	Main contents: rainfall history forecasting rainfall misleading WaterCorp graphic climate change forest thinning Harvey water Cloud seeding Questions for Water Corporation Perth Waters Users Group Including comments on Government 29 July go ahead for seawater desalination plant Feb 05 comments on WaterCorp press claims re MANJIMUP water supply issues

Read how CSIRO Chief made incorrect claims re SW WA rainfall data on ABC TV 7.30 Report
Summary: The 2001-2003 water shortage in Perth and low dam levels represents a challenge for ratepayers and voters.
The Government line is that climate change is the cause and expensive new desalination facilities are a part of the solution.
The truth is that decades of forest regrowth and a lack of catchment management due to prevailing Green dogmas has suppressed streamflows and made a significant contribution to the current situation along with slightly lowered rainfall of the last 30 years. The process of catchment degradation is continuing, wasting too much of catchment rainfall.
2003 rainfall for Perth at 853 mm was above the average (791) for the years since 1975 and figures for 2004 ; dam levels have improved and there seems no rational reason to expect that rainfall ahead will not oscillate around the 800 mm PA level, as it has for 130 years that we know about. A more balanced approach is required by the Government before Perth people are saddled with the most expensive city water in Australia. Unnecessary spending on a massive desalination plant to augment the Perth water supply must affect other Government expenditure on schools, hospitals etc, there is no bottomless pit of public money. .

Perth rainfall history 1876-2004

The above graphic demonstrates clearly that there has been no decline in rainfall which would imperil supplies to the point where we have to consider expensive desalination options. 2001 was only the 15th dryest year since records began in 1876. What has happened to cause our water shortage is that consumption is ever rising, catchments are being steadily degraded by scrub regrowth impairing runoff and we have been less than prudent over a decade or more in putting off projects that could have brought on new supplies from dams.

Rainfall near the catchments is of course more relevant to dam storage than Perth rain and this map by Martyn Keen, WA Dept. of Agriculture shows how catchment rain is so much higher than Perth. Click on map for larger version. Click here for full map and legend.
Click for Dwellingup rain history and we see that 2001 was a dryer year relatively than in Perth. How blessed we are to be averaging a metre of rain per year so close to Perth. Government proponents of the "Perth water crisis" including the CSIRO often say that since the mid 1970's there has been a 20% reduction in rainfall in SW WA including Perth. My figures for Dwellingup show an average of 1313.8 mm 1934-1974 then 1181.8 mm from 1975-2003, so there has been 132 mm decrease since 1974 which to my way of thinking equates to a 10.05% reduction.

In the case of Perth, there was an average 880.3 mm of rain per year from 1876 to 1974 and 791.2 mm 1975 to 2003, a drop of 89.1 mm per year which equates to a 10.12% reduction in annual rainfall. I am still looking for the 20%.

What the Government should do in 2004/5.

The Kwinana desalination plant project should be put on hold and only a research role maintained.
A program of catchments management and bush thinning must start so runoff will improve.
Replace planned production from desalination with projects from The Water Corporations "pipeline" of engineering projects.
A tiny proportion of the money to be wasted on the desalination plant should be diverted to a cloud seeding project this winter and spring, now.
The cutting of the Gnangara pines should be brought forward, on the basis that the groundwater they are suppressing (valued at the production of Kwinana desal plant) means they have no net present value. Govt. should heed UWA proposal to convert Gnangara pines in a decade to a mix of new urban areas and native vegetation, freeing up 130 GL per year of groundwater.
The Agritech proposal to desalinate Wellington Dam wastewater looks too good not to take up.
The Premier could then announce that the money saved could contribute to schools, hospitals etc.

All too easy but Hey !!, would the Greens be happy ?

The composite graphic below sums up major trends relevant to the debate on Perth water supplies, data (except BoM rain fall) extracted from Water Corporation Annual Reports.

Salient points are;

Consumption rising but trimmed by belated sprinkler restrictions in 2002-3,
dam production at early 1980's levels in 2002-3,
ground water use drastically increased,
no trend in rainfall from 1979-2003; will switch to a better average for catchments when I have the data,
storage starting to recover after being too low for six years and rarely over 50% in last 15 years.

I am sure readers will correct me if I am wrong here but the contents of this web page are based on the assumption that our society through elected Governments plans for its future needs and welfare employing experts such as engineers, scientists and economists who should have due regard to rational facts and the most accurate histories of natural data possible. If this is not done we run the risk of basing policy on belief, which puts us closer to Witch Doctor or Cargo Cult societies.

The issues I am commenting on critically are mainly those that I can see have been inadequately dealt with to date.
These are;

historic rainfall data,
could more be done in forecasting rainfall for next few years, see work by Dr. Warren B. White,
the misleading streamflow graphic produced by The Water Corporation to be often used in their reports and now even more misleading on the new ourwaterfuture web site,
proposals to pipe a tiny fraction of Kimberley water to Perth are always shot down on cost but we should be looking at this water being piped south in the context of a "Nation Building" project linked to new migration above the 26th parallel,
unproductive bleating about "climate change" - as if climate is ever not changing,
the issue of selective logging and bush management in catchments which could increase stream flows to levels of some decades ago,
there is much evidence that cloud seeding has beneficially increased rainfall in many Australian locations yet this is never considered in respect of the Perth water shortage.
half of Perth's water supply comes from groundwater

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