Using paleoclimate reconstructions to analyse hydrological epochs associated with Pacific Decadal Variability

Abstract

Abstract. The duration of dry or wet hydrological epochs (run lengths) associated with positive or negative Inter-decadal Pacific Oscillation (IPO) or Pacific Decadal Oscillation (PDO) phases, termed Pacific Decadal Variability (PDV), is an essential statistical property for understanding, assessing and managing hydroclimatic risk. Numerous IPO and PDO paleoclimate reconstructions provide a valuable opportunity to study the statistical signatures of PDV, including run lengths. However, disparities exist between these reconstructions making it problematic to determine which reconstruction(s) to use to investigate pre-instrumental PDV and run length. Variability and persistence on centennial scales are also present in some millennium long reconstructions, making consistent run length extraction difficult. Thus, a robust method to extract meaningful and consistent run lengths from multiple reconstructions is required. In this study, a dynamic threshold framework to account for centennial trends in PDV reconstructions is proposed. The dynamic threshold framework is shown to extract meaningful run length information from multiple reconstructions. Two hydrologically important aspects of the statistical signatures associated with the PDV are explored: (i) whether persistence (i.e. run lengths) during positive epochs is different to persistence during negative epochs and (ii) whether the reconstructed run lengths are stationary during the past millennium. Results suggest that there is no significant difference between run lengths in positive and negative phases of PDV and that it is more likely than not that the PDV run length has been non-stationary in the past millennium. This raises concerns about whether variability seen in the instrumental record (the last ~ 100 years), or even in the shorter 300–400 year paleoclimate reconstructions, is representative of the full range of variability.

Comparison of published palaeoclimate records suitable for reconstructing annual to sub-decadal hydroclimatic variability in eastern Australia: implications for water resource management and planning

“…This is consistent with the findings from other studies (e.g. Zhang et al, 2018;Dixon et al, 2019) and again suggests that the last ~200 years is unusual and that multidecadal-scale persistence rather than more frequent fluctuations between wet and dry conditions has dominated most of the last 1000 years.…”

“…However, palaeoclimate-based reconstructions of past hydroclimatic variability come with their own uncertainties, assumptions, and limitations (e.g. Tozer et al, 2016Tozer et al, , 2018Dixon et al, 2017Dixon et al, , 2019Zhang et al, 2018). Consequently, as also recommended in Kiem et al (2016), further research is needed to (i) better understand, quantify, and deal with uncertainties and inconsistencies in the palaeoclimate information and (ii) provide the translational science required for water resources managers and planners to maximise the practical value of palaeoclimate records in assessing and managing drought and flood risks.…”

“…As documented in previous studies (e.g. Tozer et al, 2016Tozer et al, , 2018Dixon et al, 2017Dixon et al, , 2019Zhang et al, 2018), and as evident from Section S1 in the Supplementary Material, there are numerous sources of uncertainty associated with palaeoclimate records and lack of agreement across different sources of palaeoclimate https://doi.org/10.5194/hess-2020-314 Preprint. Discussion started: 30 June 2020 c Author(s) 2020.…”