The State Government is using outdated data to underpin the next 10-year South West forests blueprint, provoking outrage from conservationists who say the move makes a mockery of scientific process.
Documents released under Freedom of Information laws reveal the Government will use rainfall figures from 1961 to 1990 as a baseline for setting logging targets in the next Forest Management Plan.
The statistics will be a cornerstone of the plan, which will run from 2014 to 2023, because rainfall assumptions are a key part in determining how many trees can be logged each year.
But the Government said the figures were only a starting point and any final decisions would take account of climate projections by the CSIRO, Australia's top scientific organisation.
A spokeswoman for Environment Minister Bill Marmion said yesterday these projections would be based on expected changes to "climate parameters", including temperature and rainfall to 2070.
"CSIRO's climate change severity scenarios have been used for modelling the potential impacts of climate change on sustained timber yields," she said.
WA Forest Alliance spokeswoman Jess Beckerling said it was scandalous the Government was using old rainfall figures rather than current ones because totals had fallen about 10 per cent since 1990.
She said forestry targets should be set according to reliable rainfall data and assuming redundant, higher figures would lead to unsustainable logging and an environmental disaster.
"Obviously, forests and rain have a critical relationship," Ms Beckerling said. "Whether it's forest health and biodiversity or the recovery time after logging or the productive capacity or the areas you can log - all of those things rely on rainfall information.
"So if your rainfall data is inaccurate, the whole plan is going to be inaccurate."
Shadow environment minister Sally Talbot said the Government, through the Department of Environment and Conservation, was hijacking a scientific process.