Creating forecasts of cattle heat stress for Australia: challenges and prototypes

In Australia, a heatwave is defined as a run of unusually high daytime and night-time temperatures persisting for three or more days and is routinely forecast by the Bureau of Meteorology through its heatwave service, primarily to support human health and community safety. No equivalent spatial heat stress forecasts currently exist for Australian cattle or other grazing livestock, creating an important information gap. Here, we introduce 7-day prototype spatial forecasts of cattle thermal stress for Australia, derived from the bureau’s numerical weather prediction system. These forecasts are based on commonly used thermal stress metrics, including the Temperature–Humidity Index, Heat Load Index, and the Cattle Comfort Index. Our results demonstrate that the forecast system was able to predict a significant cattle heat stress event across southern Queensland in late January 2024 with useful skill out to approximately 5 days. Beyond this lead time, forecast errors increased, largely due to difficulties in predicting relative humidity and wind speed. A similar decline in forecast skill with lead time was found for other regions, based on verification of thermal stress forecasts spanning the 2022/23 and 2023/24 austral summers. Accurately forecasting cumulative heat load remains challenging due to inherent prediction system errors at forecast initialisation. Overall, this study highlights both the potential value and current limitations of a national thermal stress forecast system for Australia’s grazing livestock, relative to existing subscription-based services. The nationally consistent spatial forecast prototypes presented here provide meaningful early guidance for graziers managing heat risk on their properties and have the potential to improve livestock welfare outcomes in the future.