A Drought Monitor for Australia

Drought management is one of the most serious challenges that producers in the Australian agricultural industry can face. However, drought is complicated and often associated with multiple variables such as rainfall, atmospheric evaporative demand, and antecedent soil moisture conditions. For these reasons, managing drought using a single index or indicator is not always effective, but most existing drought information services in Australia rely on this approach. This study introduces the Drought Monitor and Australian Combined Drought Indicator (CDI), which uses a multi-index approach to capture the symptoms of both short-term meteorological drought and longer-term agricultural drought. Climate variables used as inputs for the CDI are evapotranspiration (ET), the Normalized Difference Vegetation Index (NDVI), soil moisture (SM), and the Standardized Precipitation Index (SPI). These inputs are consolidated using a normalized linear combination where their percentage contribution (or weights) are derived using a principal component analysis (PCA) to specifically calibrate the index for Australia to achieve maximum variance. The CDI was evaluated against observed wheat yield and cattle death rate, as well as total pasture growth simulated by the AussieGRASS model. The results indicate that the CDI has a significant positive correlation with wheat yield and total pasture growth. The Drought Monitor was also well-received by survey respondents, and has the potential to become a valuable drought monitoring tool for identifying drought impacts and related risks, supporting decision-making in government policy, and assisting Australian producers to prepare for and adapt to future drought changes.