Variability of Soil Moisture Proxies and Hot Days Across the Climate Regimes of Australia

The frequency of extreme events such as heatwaves are expected to increase due to the effect of climate change, particularly in semi-arid regions areas of Australia. Recent studies have indicated a link between soil moisture deficits and heat extreme, focusing on the coupling between the two. This study investigates the relationship between the number of hot-days (Tx90) and four soil moisture proxies (SPI, API, MSDI and KBDI), and how the strength of this relationship changes across various climate regimes within Australia. A strong anti-correlation between Tx90 and each moisture index is found, particularly for tropical savannas and temperate regions. However, the magnitude of the increase in Tx90 with decreasing moisture is strongest in semi-arid and arid regions. It is also shown that the Tx90-soil moisture relationship strengthens during the El Nino phases of ENSO in regions which are more sensitive to changes in soil moisture.