Unprecedented high northern Australian streamflow linked to an intensification of the Indo-Australian monsoon

Streamflow in Australia's northern rivers has been steadily increasing since the 1970s, most likely due to increased intensity in the Indo-Australian monsoon. However, because of limited data availability, it is hard to assess this recent trend and therefore contextualize potential future climatic changes. In this study, we used a network of 63 precipitation-sensitive tree-ring chronologies from the Indo-Australian and Asian monsoon regions to reconstruct streamflow in the Daly catchment in the Northern Territory of Australia from 1413 to 2005 CE. We used a novel wavelet-based method to transform the variance structure of the tree-ring chronologies to better match the hydroclimate prior to reconstruction with a hierarchical Bayesian regression model. Our streamflow reconstruction accounts for 72%-78% of the variance in the instrumental period and closely matches both historical flood events and independent proxy records, increasing confidence in its validity. We find that while streamflow has been increasing since the 1800s, the most recent 40-year period is unprecedented in the last similar to 600 years. Comparison to an independent coral-based streamflow record shows regional coherency in this trend. Extreme high flows were found to be linked to La Nina events, but we found no significant relationship between streamflow and El Nino events, or streamflow and other regional climatic drivers. More work is therefore needed to understand the drivers of the recent streamflow increase, but, regardless of the cause, water managers should be aware of the paleoclimatic context before making decisions on water allocations.