Heat and Moisture Anomalies During Crop Failure Events in the Southeastern Australian Wheat Belt

Prolonged droughts and heatwaves are common causes of agricultural failure in Australia, yet the origins of these climate anomalies remain understudied. Here, we use a Lagrangian trajectory model driven by atmospheric reanalysis and constrained by satellite data to unravel the sources of precipitation and heat over the Southeastern Australia wheat belt. Furthermore, we assess the impact of local and upwind drought conditions on the moisture and heat imports to the region. Results indicate that the most extreme crop failure events over the wheat belt (i.e., 1994, 2002, and 2006) were associated with persistent high-pressure systems. The ocean provided on average 72% of the moisture for precipitation and 39% of the heat arriving over the wheat belt, with the moisture sources substantially decreasing during crop failure events. Upwind drought further intensified rainfall deficits and heat stress during these events due to lower moisture and higher heat imports to the region. This was particularly clear during the initial phase of the Millennium Drought in 2002. Then, yield deficits exceeded 50%, and similar to 4% of the precipitation originated from drought-affected regions upwind, compared to the 9% that was expected climatologically from those regions. Simultaneously, the heat import from these regions upwind increased by similar to 10 W m-2, from the climatological 23%-25%, during this event. While these results indicate a limited potential for upwind land management to mitigate downwind agricultural loss in the Southeastern Australia wheat belt, other agricultural regions with a higher climatic dependency on remote land may benefit from such strategies. Droughts and heatwaves are posing threats to wheat production worldwide. In Australia, one of the largest wheat producers, the relationship between crop yield and climate anomalies remains understudied. Here, we use a novel framework dedicated to track heat and moisture across the atmosphere, which enables the identification of the sources of precipitation and temperature over the Southeastern Australia wheat belt, and the quantification of the influence of droughts on agricultural productivity. Results show that upwind droughts intensify precipitation deficits and heat stress by providing less moisture and more heat to the wheat belt during the years in which wheat production decays. This holds potential implications for land use management strategies dedicated to ensuring agricultural food supply by influencing weather patterns. Crop failure events in the Australian wheat belt relate to anomalies in precipitation and its contribution from land and oceanic origins Land surfaces provide less moisture but more heat than the oceans and this difference tends to be aggravated during crop failure events Upwind droughts amplify the precipitation deficits and heat accumulation in the Australian wheat belt