Science Advances

Supplementary Materials

This PDF file includes:

  • Introduction
  • OWDA as a scientific advancement over previous work
  • Gridded monthly scPDSI target field
  • OWDA tree-ring network
  • Climate sensitivity of OWDA tree-ring chronologies
  • Validation of OWDA tree-ring climate response
  • Augmenting tree-ring chronologies with historical tree-ring data
  • Standardizing OWDA tree-ring data for climate reconstruction
  • Standardizing OWDA historical/modern tree-ring data
  • Estimating low- to medium-frequency variance retention
  • Point-by-point regression
  • Comparisons with Pauling spring-summer precipitation reconstructions
  • Additional validation tests of the OWDA
  • References
  • Table S1. List of tree-ring chronologies used for producing the OWDA.
  • Fig. S1. Map of the OWDA domain showing 5414 half-degree grid points of JJA scPDSI (small black dots) and the 106 annual chronology tree-ring network (red and blue triangles).
  • Fig. S2. Maps, by decade (up to 1950), of the changing densities of precipitation stations (solid red dots) available for interpolation on the half-degree regular grid used to produce the CRU TS precipitation field (
  • Fig. S3. Comparisons of calibration period (1928–1978) and validation period (1901–1927) scPDSI averages and their variances.
  • Fig. S4. Statistical properties of gridded summer scPDSI data over the 1928–1978 calibration period and tests of normality using a simple and robust test of normality based on joint use of skewness and kurtosis (69).
  • Fig. S5. CDL between 5414 grid points of summer scPDSI used for reconstruction over the OWDA domain.
  • Fig. S6. Summary maps of correlations between summer scPDSI and the tree-ring network over the 5414 grid points of the OWDA domain calculated for the 1928–1978 calibration period, using the PPR program in the same way that it was used to produce the OWDA reconstructions.
  • Fig. S7. Example of a historical/modern tree-ring chronology from northeastern France developed by the iterative procedure described in the text.
  • Fig. S8. Overlay plots of Tornetrask power spectra (frequencies from 0 to 0.1) for different detrending options before (RCS/SSD) and after (SF-RCS/SSD) the application of the signal-free method to the data using the same curve-fitting options: Opt 0—RCS detrending (designed to preserve the most low- to medium-frequency variance); Opt 1—negative exponential/linear detrending (monotonic nonincreasing, least flexible SSD option); Opt 2—cubic smoothing spline detrending based on the median segment length of the data (moderately dataadaptive, fixed intermediate flexibility); and Opt 3—the Friedman variable span smoother (locally adaptive, very flexible).
  • Fig. S9. Example of the two-stage SF-RCS method applied to the historical/modern Quercus species (QUSP) tree-ring data of northeastern France used as an example by Auer et al. (48).
  • Fig. S10. Additional low- to medium-frequency variance retained in the historical/modern tree-ring chronologies using the two-stage SF-RCS procedure.
  • Fig. S11. Calibration and validation statistical maps of the eight-member ensemble-average OWDA reconstructions.
  • Fig. S12. Correlations of OWDA JJA scPDSI reconstructions with Pauling spring-summer precipitation reconstructions primarily reconstructed from long instrumental and historical climate indices (18).
  • Fig. S13. Comparison of OWDA and Pauling maps for 1540 (“year-long unprecedented European heat and drought”) (21).
  • Fig. S14. Maps of exceptional droughts in Czech lands (20).
  • Fig. S15. Maps of the great European famine (22).
  • Fig. S16. OWDA mean and median maps for nine noteworthy 17th-century droughts over England and Wales: 1634, 1635, 1636, 1666, 1667, 1684, 1685, 1694, and 1695 (33).
  • Fig. S17. OWDA mean and median maps for eight noteworthy Ottoman Empire droughts: 1570, 1591, 1592, 1594, 1595, 1607, 1608, and 1610 (107).
  • Fig. S18. OWDA mean and median maps for 12 noteworthy pre-1450 historical droughts in England and Wales: 1084, 1129, 1136, 1222, 1242, 1252, 1263, 1272, 1284, 1288, 1305, and 1385 (110).
  • References (45–110)

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