The variability of 'nature's limit' in South Australia

The 1864/65 drought that hit South Australia prompted the establishment of Goyder’s Line, which has long been known in the State as the division between land suitable for cropping and land only viable for pasture. Current cropping areas however extend beyond this line, suggesting that either a) the line is not well defined, b) cropping is currently occurring on ‘non-viable’ land or c) the line is variable from year to year. In this study, the 220 mm growing season (April to October) rainfall isohyet is used as a proxy for SA’s cropping boundary in order to assess its temporal and spatial variability. Using indices of the El Niño/Southern Oscillation, Indian Ocean Dipole, Southern Annular Mode and the Subtropical Ridge, it is shown that climate state significantly influences the location of the 220 mm growing season rainfall isohyet. This implies that the boundary between viable and non-viable cropping areas (i.e. “nature’s limit”) is non-stationary. These results also indicate the key influences on South Australia’s climate and have important implications globally for agricultural practices operating in or bordering semi-arid environments.