Some farmers are predicting a billion-dollar loss to the grain industry after an unusually warm and dry start to winter in Western Australia.

WA Farmers president Tony York says, at best, many farmers are looking at an average season but it may be much worse without more substantial rainfall this month.

He predicts a 20 per cent drop in the value of grain crops compared to last year, which equates to $1 billion less in revenue.

But Grain Industry Association of WA executive member Michael Lamond says it's too early to make that call, adding that while it would not be a catastrophic season, some farmers could still lose a year's worth of income.

"It's not too good. It's unusual not to get any rain or very little rain in May-June," he told AAP on Monday.

"It's not unusual to have a break in the season ... but we're getting past that now."

Bureau of Meteorology duty forecaster Ricus Lombard says the generally dry start to winter is being experienced across the state and Perth is on track to have its warmest June on record.

He said Perth had averaged 23C for the first two weeks of winter and received 26mm of rain, which was well below the 172mm average for the month but there would be some rainfall this week.

Water minister Dave Kelly said the South West region was being affected by climate change, evidenced by the fact dams used to collect 300 gigalitres of water to supply Perth, which had dropped to about 25 gigalitres.

"We used to think that if you want to be waterwise you're going to have to live in a bit of a dust bowl," he told ABC radio.

"You can actually have a really liveable city, which is green but waterwise at the same time and that depends on how we manage our gardens (and) how we build our suburbs.

"The last thing I want to do in the current state of the books is tell the treasurer he needs to find another $1 billion for a desalination plant."

AAP

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