Evolving patterns of compound heat and water stress conditions: Implications for agriculture futures in Australia

Australia's agriculture has faced prolonged extreme heat and drought periods, leading to significant economic and agricultural losses. Climate projections show a rising risk of droughts and heatwaves in Australia, making it essential to understand these dynamics for effective planning and adaptation. We define agricultural heat and/or water stress (AgHWS) indices using crop and soil physiology thresholds. This crop-specific approach enhances our analysis of compound events' impacts on agricultural commodities. We examine both the compound and individual AgHWS conditions, tracking their changes through time. This is achieved through the implementation of historical reconstruction (back to 1961) and future projections (to 2099) using suitable CMIP5 models for Australia. For this, we utilise daily temperature and soil moisture data from the Australian Bureau of Meteorology's high-resolution (0.05°) National Hydrological Projections using CMIP5 climate forcing together with the Australian Water Resources Assessment – Landscape (AWRA-L) model. These projections are examined under two Representative Concentration Pathways (RCP4.5 and RCP8.5) and are compared to historical outputs from the AWRA-L model. Results indicate that: (1) AgHWS conditions are projected to increase in frequency, and intensity in future years with earlier onsets and prolonged durations across Australia; (2) AgHWS duration will rise from approximately 10 days per event in the late historical period to around 30 days per event for RCP 4.5, and 50 days per event for RCP 8.5 in the late future; (3) Northern Australia is projected to be severely impacted by AgHWS conditions while agricultural regions in south-eastern and south-western Australia appear to be less so; and (4) Water stress contributes most to the creation of AgHWS conditions, underscoring the importance of soil water conservation management. By analysing the spatio-temporal patterns of changes in both individual and compound AgHWS conditions, this study can support decision-making and helps inform targeted adaptation strategies for the agricultural sector across Australia.