Rainfall levels in the Riverina are generally low with the median annual rainfall over most of the region between , rising to between on the eastern fringe.
One method of classification of boundaries for the Riverina is the Interim Biogeographic Regionalisation for Australia that defines the bioregion as an area comprising , with biogeographic subregions covering each of the Lachlan, Murrumbidgee, Murray Fans, Victorian Riverina, Robinvale Plains, and Murray Scroll Belt [REF].