Australia’s Murray-Darling Basin experienced three consecutive years of meteorological drought across 2017–2019, collectively named the ‘Tinderbox Drought’. Rainfall deficits during the three-year drought were focussed in the Australian cool season (April to September), and deficits in both the cool season and the annual total were unprecedented in the instrumental record. However, at ~120 years long, Australian rainfall records are not long enough to have captured the full possible range of variability, particularly for multi-year extreme events. That is, observations are an incomplete sampling of the full possible range of rainfall variability. Climate model simulations may provide longer timeseries, however climate models have known biases in Australian rainfall (Grose et al. 2020). Therefore, to determine if the Tinderbox Drought was outside the expected range of internal variability, we constructed Linear Inverse Models (LIMs) that simulate internal variability in Australian rainfall and associated global sea surface temperature (SST) anomalies. We used the LIMs to produce 10000-year-long rainfall records that emulate the stationary statistics of observed Australian rainfall, hence reflecting more of the full possible range of variability.   Overall, we find that rainfall deficits were most severe 1) in the northern Murray-Darling Basin; and 2) during the final year of the drought (2019). Global SST anomalies during the drought mostly did not resemble the pattern that is most reliably associated with low rainfall over the Murray-Darling Basin (warm anomalies in the central tropical Pacific and the western Indian Ocean). In fact, global SST anomalies observed during the Tinderbox Drought are not reliably associated with negative rainfall anomalies across the Murray-Darling Basin—this is particularly the case for the first two years of the drought. In terms of single-year rainfall anomalies, the only aspect of the Tinderbox Drought that was beyond the expected natural range was annual-total rainfall over the northern Murray-Darling Basin during 2019. However, when considered in terms of basin-wide rainfall over the full three years, negative anomalies during the Tinderbox Drought were beyond the expected natural range in terms of both cool season and annual rainfall. This suggests an anthropogenic contribution to the severity of the drought. Additionally, we find that Linear Inverse Models are a valuable tool for estimating whether or not an observed extreme rainfall event falls within the expected natural range. References Grose, M. R., Narsey, S., Delage, F. P., Dowdy, A. J., Bador, M., Boschat, G., et al. (2020). Insights from CMIP6 for Australia's future climate. Earth's Future, 8, e2019EF001469.
The climate of the past two thousand years (2k) provides context for current and future changes, and as such is vital for developing our understanding of the modern climate system. Building on previous phases of the PAGES 2k network, Phase 4 of the PAGES 2k Network paves the way for a new level of understanding of the global water cycle, including enhanced science-policy integration. Previous PAGES 2k network phases emphasised temperature reconstructions, fundamentally improving our understanding of global climate changes over the Common Era. These reconstructions received widespread recognition and were featured in the Summary for Policymakers of the IPCC’s Sixth Assessment Report. Integration of this data with state-of-the-art Earth systems models, proxy system models and data assimilation yielded a more comprehensive understanding of the associated physical drivers and climate dynamics.  Phase 4 challenges our community to turn its focus towards hydroclimate. Our aim is to reconstruct hydroclimatic variability over the Common Era, from local to global spatial scales, at sub-annual to multi-centennial time scales, developing a process-level understanding of past hydroclimate events and variability. Our multi-faceted approach includes (1) developing new hydroclimate syntheses that are well-suited for data-model comparisons, (2) improving the interoperability and scope of existing data and model products, and (3) facilitating the translation of our science into evidence-based policy outcomes. In this presentation, we report on our activities and progress to date, particularly highlighting the early stages of our data synthesis efforts.
Data & code repository for Forced changes in the Pacific Walker circulation over the past millennium This repository contains scripts and auxiliary data necessary for recreating the figures in the paper Forced changes in the Pacific Walker Circulation over the past millennium (https://doi.org/10.1038/s41586-023-06447-0) [published in Nature October 2023; available online August 2023]. The code is tested with R version 4.1.2. Repository Structure `Falster_PWCreconstructions`: zipped folder contains our ensemble reconstruction of ΔSLP (1200-2000 CE) `Falster2022_PWC_reconstruction.csv`: a csv with one column per ensemble member. Column headers state the reconstruction method, and gridded SLP product used to train the reconstruction (200 ensemble members per unique combination of reconstruction method and training index). `Falster2022_PWC_reconstruction.xlsx`: Excel workbook, with one tab per unique combination of reconstruction method and training index (200 ensemble members each). `Falster2022_PWC_reconstruction_full_ensemble_median_and_95pct_range.csv`: a csv with the median and 95% range (2.5th and 97.5th percentiles) of the full 4800-member ΔSLP reconstruction ensemble. Includes raw summary values, and summary values with a five-year running mean. For robust analysis of ΔSLP, we strongly recommend working with the full ensemble rather than these summary values. `Falster_PWCreconstruction_code`: zipped folder contains scripts and auxiliary data necessary to generate figures in the main text `scripts`: contains R scripts necessary to generate figures in the main text `Figure1`: folder containing scripts to perform analysis and generate Fig. 1 in the main text `Figure2`: folder containing scripts to perform analysis and generate Fig. 2 in the main text `Figure3`: folder containing scripts to perform analysis and generate Fig. 3 in the main text `Figure4`: folder containing scripts to perform analysis and generate Fig. 4 in the main text `Figure5`: folder containing scripts to perform analysis and generate Fig. 5 in the main text `Figure6`: folder containing scripts to perform analysis and generate Fig. 6 in the main text `data`: contains all auxiliary data necessary for the analysis and visualisation, including: reconstructions in .rds format shapefiles for mapping processed ΔSLP and Nino 3.4 RSST timeseries from the CESM1 LME and PMIP3/4 models How to cite this repository If using code or data from this repository, please cite the original publication, available from https://www.nature.com/articles/s41586-023-06447-0. This repository can be cited with https://doi.org/10.5281/zenodo.7742760.
Geochemical data for Lake Surprise, a crater lake located in western Victoria, southern Australia. Scanning XRF data (Si, Ti, Fe, Mn, Ca, S), calibrated to percentages. Carbon isotope composition of bulk sediment organic matter. Chronology derived from radiocarbon dates from concentrated pollen samples.
We examine the characteristics and causes of southeast Australia's Tinderbox Drought (2017 to 2019) that preceded the Black Summer fire disaster. The Tinderbox Drought was characterized by cool season rainfall deficits of around -50% in three consecutive years, which was exceptionally unlikely in the context of natural variability alone. The precipitation deficits were initiated and sustained by an anomalous atmospheric circulation that diverted oceanic moisture away from the region, despite traditional indicators of drought risk in southeast Australia generally being in neutral states. Moisture deficits were intensified by unusually high temperatures, high vapor pressure deficits, and sustained reductions in terrestrial water availability. Anthropogenic forcing intensified the rainfall deficits of the Tinderbox Drought by around 18% with an interquartile range of 34.9 to -13.3% highlighting the considerable uncertainty in attributing droughts of this kind to human activity. Skillful predictability of this drought was possible by incorporating multiple remote and local predictors through machine learning, providing prospects for improving forecasting of droughts.
The Pacific Walker Circulation (PWC) has a major influence on weather and climate worldwide. But our understanding of 1) its response to external forcings; and 2) its internal variability across timescales remain unclear. This is in part due to the length of the observational record, which is too short to disentangle forced responses from internal variability.  Here we assess the internal variability of the PWC as well as its response to the two largest external forcings of the Common Era: volcanic eruptions and anthropogenic forcing. We do this using a new annually-resolved, multi-method, palaeoproxy-derived PWC reconstruction ensemble spanning 1200-2000. The reconstruction is derived from 59 palaeoclimate proxy records, mostly from the Iso2k database of water isotope proxy records (Konecky et al., 2020). The basis for the reconstruction is previous work by Falster et al. (2021), demonstrating that global water isotope variability has a strong mechanistic link with the PWC via its major influence on the global water cycle. The PWC reconstruction ensemble comprises 4800 members that sample uncertainty from observational data, reconstruction method, and record chronologies.  We identify a significant PWC weakening in the 1-3 years following large volcanic eruptions, similar to the response seen in some climate models. However, we find no significant industrial-era (1850-2000) PWC trend relative to the preceding 650 years, which contrasts the PWC weakening simulated by most climate models. In fact, the strength of the PWC is not correlated with global mean temperature across timescales. We also find that the 1992-2011 PWC strengthening—previously attributed either to volcanic or anthropogenic aerosol forcing—was indeed anomalous, but not unprecedented as compared to the past 800 years. Hence it may have occurred due to decadal internal variability. The one place we did identify an industrial-era PWC change is in the power spectrum, where a post-1850 shift to lower-frequency variability suggests a subtle anthropogenic influence.  References: Konecky, B. L., McKay, N. P., Churakova (Sidorova), O. V., Comas-Bru, L., Dassié, E. P., DeLong, K. L., Falster, G. M., Fischer, M. J., Jones, M. D., Jonkers, L., Kaufman, D. S., Leduc, G., Managave, S. R., Martrat, B., Opel, T., Orsi, A. J., Partin, J. W., Sayani, H. R., Thomas, E. K., Thompson, D. M., Tyler, J. J., Abram, N. J., Atwood, A. R., Cartapanis, O., Conroy, J. L., Curran, M. A., Dee, S. G., Deininger, M., Divine, D. V., Kern, Z., Porter, T. J., Stevenson, S. L., von Gunten, L., and Iso2k Project Members: The Iso2k database: a global compilation of paleo-δ18O and δ2H records to aid understanding of Common Era climate, Earth Syst. Sci. Data, 12, 2261–2288, 2020. Falster, G., B. Konecky, M. Madhavan, S. Stevenson, and S. Coats: Imprint of the Pacific Walker Circulation in Global Precipitation δ18O. J. Climate, 34, 8579–8597, 2021.
Data & code repository for Forced changes in the Pacific Walker circulation over the past millennium This repository contains scripts and auxiliary data necessary for recreating the figures in the paper Forced changes in the Pacific Walker Circulation over the past millennium (https://doi.org/10.1038/s41586-023-06447-0) [published in Nature October 2023; available online August 2023]. The code is tested with R version 4.1.2. Repository Structure `Falster_PWCreconstructions`: zipped folder contains our ensemble reconstruction of ΔSLP (1200-2000 CE) `Falster2022_PWC_reconstruction.csv`: a csv with one column per ensemble member. Column headers state the reconstruction method, and gridded SLP product used to train the reconstruction (200 ensemble members per unique combination of reconstruction method and training index). `Falster2022_PWC_reconstruction.xlsx`: Excel workbook, with one tab per unique combination of reconstruction method and training index (200 ensemble members each). `Falster2022_PWC_reconstruction_full_ensemble_median_and_95pct_range.csv`: a csv with the median and 95% range (2.5th and 97.5th percentiles) of the full 4800-member ΔSLP reconstruction ensemble. Includes raw summary values, and summary values with a five-year running mean. For robust analysis of ΔSLP, we strongly recommend working with the full ensemble rather than these summary values. `Falster_PWCreconstruction_code`: zipped folder contains scripts and auxiliary data necessary to generate figures in the main text `scripts`: contains R scripts necessary to generate figures in the main text `Figure1`: folder containing scripts to perform analysis and generate Fig. 1 in the main text `Figure2`: folder containing scripts to perform analysis and generate Fig. 2 in the main text `Figure3`: folder containing scripts to perform analysis and generate Fig. 3 in the main text `Figure4`: folder containing scripts to perform analysis and generate Fig. 4 in the main text `Figure5`: folder containing scripts to perform analysis and generate Fig. 5 in the main text `Figure6`: folder containing scripts to perform analysis and generate Fig. 6 in the main text `data`: contains all auxiliary data necessary for the analysis and visualisation, including: reconstructions in .rds format shapefiles for mapping processed ΔSLP and Nino 3.4 RSST timeseries from the CESM1 LME and PMIP3/4 models How to cite this repository If using code or data from this repository, please cite the original publication, available from https://www.nature.com/articles/s41586-023-06447-0. This repository can be cited with https://doi.org/10.5281/zenodo.7742760.
1500-year stable carbon and oxygen isotopes in larch tree-ring cellulose from the Altai-Sayan Mountain Range region (49-51N, 87-89 E) Regional summer (June-July-August) precipitation reconstruction for the Altai-Sayan Mountain Range region based on d13C in tree-ring cellulose (d13Ccell ) combined with Co/Inc and Rb/Sr from Teletskoe Lake core sediments (TLs).Regional summer air temperature (June-July-August) reconstruction based on d18Oin tree-ring cellulose (d18Ocell), tree-ring width (TRW), latewood density (MXD) and elemental concentrations (Ca, Ti, Br/Sr) in the Teletskoe Lake core sediments (TLs).
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