Understanding the origins of climate anomalies during low-yield years in Australia’s largest breadbasket

Wheat yield in Australia is highly dependent on year-to-year climate variability. Prolonged droughts and anomalously high temperatures have been considered as causes of agricultural failures in recent years. However, the origins of these climate extremes and their impacts on yield remain under study. Here, we use a Lagrangian trajectory model driven by atmospheric reanalysis data to delineate the source regions of moisture and heat over Australia’s largest rainfed agricultural region. In particular, we focus on extreme crop failure years (1994, 2002, 2006) and analyze the impact of upwind droughts on heat and moisture imports into the region. Our results indicate that low-yield years are often associated with stable high-pressure systems that lead to a decreased import of moisture from the surrounding oceans. Within the breadbasket, however, this caused higher-than-usual surface sensible heating. Moreover, the analyzed low-yield years coincide with widespread droughts over the Australian continent. We find that upwind droughts can further influence moisture and heat imports to the region. During the initial phase of the Millennium Drought in 2002, crop failure over the breadbasket exceeded 50% and only around 9% of the precipitation over the region originated from (upwind) land — this constitutes a decrease of 5.0% compared to the climatological average. Simultaneously, the heat import from remote land regions increased from an average of 22.8% to 24.7% in 2002. While our findings suggest that upwind droughts played only a minor role for Australia's largest breadbasket due to the influence of oceanic contributions in the region, other agricultural areas that show a larger dependency on moisture and heat imports from the land would be more susceptible to upwind climate anomalies.