(Bloomberg) -- Severe flooding episodes across vast swathes of eastern Australia this week show no signs of relenting as costs to farmers continue to mount, with another bout of heavy rain on course to hit the already sodden growing regions over this weekend.

Grain farmers are bracing for a further deterioration in weather conditions after Australia experienced its wettest November on record in 122 years, resulting in reports of widespread quality downgrades for crops. The rains have also bogged down machinery just as growers head into what should be peak harvest season across many areas in Queensland and New South Wales.

Badly Timed Rain Hurts Australian Wheat When World Needs It Most

While the full extent of the damage is still unknown as many growers are unable to access flooded paddocks to tally up the costs, the figure could top A$1 billion ($707 million), according to the NSW Department of Primary Industries. Much of that would be put down to lost crop potential, even though Australia is still on track to produce a record wheat harvest this season.

The downpours and quality downgrades are deepening concerns about dwindling global supplies of bread-making wheat after severe drought slashed production in Canada and parts of the U.S. earlier this year. 

After the Bureau of Meteorology officially declared a La Nina event last week -- a weather phenomenon that brings greater rainfall and increased probability of cyclones and floods -- there’s unlikely to be any drastic improvement in the rain outlook over the coming months. Total falls during the December to February period are expected to be above the median for NSW, the eastern two-thirds of Queensland and Victoria state.

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