Two climate-sensitive tree-ring chronologies from Arnhem Land, monsoonal Australia

The ecology of the Australian monsoon tropics is fundamentally shaped by dry conditions between May and October followed by highly variable rainfall over the months of November to April. Due to its crucial ecological importance, a better understanding of past hydroclimate variability in the region is of great interest to land managers and custodians in this region. Short instrumental records also make highly resolved terrestrial palaeoclimate records for northern Australia prior to 1900 CE of considerable scientific importance. Here, we present two new well-replicated Callitris intratropica ring-width chronologies from Arnhem Land in northern Australia, one of which extends the tree-ring record in the region by another 86 years, back to 1761. Both chronologies have clearly defined regional patterns of correlations with temperature, precipitation, potential evapotranspiration and two drought indices (the self-calibrating Palmer Drought Severity Index (PDSI) and the Standardised Precipitation Evapotranspiration Index (SPEI)) across the lower latitudes of the Northern Territory. Results indicate considerable scope for hydroclimatic reconstructions based on C. intratropica for transitional periods into and out of the wettest time of the year. This suggests that such reconstructions would reflect variability in the duration of the wet period. While precipitation or streamflow reconstructions may be possible for both these transitional periods, drought reconstructions will be best focused on the months of March-May at the end of the wet period. Hydroclimate reconstructions would provide important baseline information for understanding the rate and magnitude of current regional climate change for these ecologically and culturally important transitional periods.