The Murray-Darling river system covers most of NSW and Victoria, so it's not hard to intuit that a drier river system will result in drier conditions in NSW and

The Murray-Darling river system covers most of NSW and Victoria, so it's not hard to intuit that a drier river system will result in drier conditions in NSW and Victoria. I don't have a source which says "the fires were predominantly caused by the drying of the river system", but given the geography it seems more unlikely (at least to me) that it didn't have a significant impact.