Comment on 'Drought variability in the eastern Australia and New Zealand summer drought atlas (ANZDA, CE 1500-2012) modulated by the Interdecadal Pacific Oscillation'

The study of (Palmer et al 2015 Environ. Res. Lett. 10 124002) details a spatial reconstruction of drought across eastern Australia and New Zealand over the last 500 years. The authors used a global 0.5° by 0.5° gridded network of the self-calibrating Palmer drought severity index (scPDSI) spanning 1901–2012 as the basis for a nested point-by-point regression to reconstruct austral summer (DJF) scPDSI for this region. Their study used 176 tree rings from New Zealand, Indonesia and Australia, and one coral record from the Great Barrier Reef. In their paper Palmer et al (2015) compared three publically available proxy records and reconstructions derived from the Law Dome ice core (East Antarctica) to their reconstructed scPDSI. These were the LD summer sea salt (LDsss) series, which is a proxy for Western Pacific sea surface temperature and subtropical eastern Australian rainfall (Vance et al 2013 J. Clim. 26 710–25, 2015 Geophys. Res. Lett. 42 129–37, Tozer et al 2016 Hydrol. Earth Syst. Sci. 20 1703–17), and two Interdecadal Pacific Oscillation (IPO) reconstructions produced using two independent methods, namely the Piece-wise Linear Fit (PLF) and Decision Tree (DT) series (Vance et al 2015 Geophys. Res. Lett. 42 129–37, 2016 Clim. Past 12 595–610). We show that the treatment of the Law Dome LDsss record and the PLF and DT IPO reconstructions mis-characterizes both the utility and targets of the three records.