Decrease in southeastern Australian water availability linked to ongoing Hadley cell expansion

Abstract

Southeastern Australia experienced the worst drought of the instrumental record from 1997 to 2009, which was broken by Australia's wettest 2 year period on record (2010/2011). This drought was primarily a cool season (April to October) phenomenon. In contrast, the breaking of the drought was a warm season (November to March) phenomenon. This reduction in winter rainfall along with an absence of very wet months led to a greater reduction in streamflow across the region than would be anticipated based on the 12% reduction in mean annual rainfall alone. The results presented in this article have linked the extent, duration, and severity of this drought to the ongoing observed expansion of the Southern Hemisphere Hadley cell at a rate of 0.5°/decade. This expansion has intensified the subtropical ridge over southern Australia, pushing cool season midlatitude storm tracks further south, leading to a reduction in winter rainfall and runoff across the region. The climate of southeastern Australia has been drying during cooler months The rainfall reduction produced a larger than anticipated reduction in runoff The drying is related to expansion of the Southern Hemisphere Hadley cell