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Northern Hemisphere hydroclimate variability over the past twelve centuries

Abstract

Accurate modelling and prediction of the local to continental-scale hydroclimate response to global warming is essential given the strong impact of hydroclimate on ecosystem functioning, crop yields, water resources, and economic security1,2,3,4. However, uncertainty in hydroclimate projections remains large5,6,7, in part due to the short length of instrumental measurements available with which to assess climate models. Here we present a spatial reconstruction of hydroclimate variability over the past twelve centuries across the Northern Hemisphere derived from a network of 196 at least millennium-long proxy records. We use this reconstruction to place recent hydrological changes8,9 and future precipitation scenarios7,10,11 in a long-term context of spatially resolved and temporally persistent hydroclimate patterns. We find a larger percentage of land area with relatively wetter conditions in the ninth to eleventh and the twentieth centuries, whereas drier conditions are more widespread between the twelfth and nineteenth centuries. Our reconstruction reveals that prominent seesaw patterns of alternating moisture regimes observed in instrumental data12,13,14 across the Mediterranean, western USA, and China have operated consistently over the past twelve centuries. Using an updated compilation of 128 temperature proxy records15, we assess the relationship between the reconstructed centennial-scale Northern Hemisphere hydroclimate and temperature variability. Even though dry and wet conditions occurred over extensive areas under both warm and cold climate regimes, a statistically significant co-variability of hydroclimate and temperature is evident for particular regions. We compare the reconstructed hydroclimate anomalies with coupled atmosphere–ocean general circulation model simulations and find reasonable agreement during pre-industrial times. However, the intensification of the twentieth-century-mean hydroclimate anomalies in the simulations, as compared to previous centuries, is not supported by our new multi-proxy reconstruction. This finding suggests that much work remains before we can model hydroclimate variability accurately, and highlights the importance of using palaeoclimate data to place recent and predicted hydroclimate changes in a millennium-long context16,17.

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Figure 1: Location map of the proxy records used in this study sorted by archive.
Figure 2: Spatial-temporal distribution of gridded centennial hydrological proxy anomalies.
Figure 3: Probability density function of reconstructed and simulated Northern Hemisphere hydroclimate and temperature anomalies.

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Acknowledgements

Funding for this work was provided in part by the Swedish Research Council (grant number C0592401), and the Navarino Environmental Observatory (NEO) (project number 1946322). E.Z.’s contribution is part of the German Cluster of Excellence CLISAP (grant number EXC177). The publication cost was covered by the Bolin Centre for Climate Research, Stockholm University, and the Department of Physical Geography, Stockholm University. This is a contribution to the Past Global Changes (PAGES) 2k Network. We thank U. Büntgen at the Swiss Federal Research Institute WSL, and H. Grudd at the Swedish Polar Research Secretariat, for comments on the manuscript.

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Authors and Affiliations

Authors

Contributions

F.C.L. and P.J.K. designed the study from an original idea by F.C.L. and P.J.K., with input from H.S.S., E.Z., G.B. and D.F. F.C.L. and P.J.K. collected all the proxy data and H.S.S. screened the records for dating uncertainties. P.J.K. produced the software used for the analyses with input from the co-authors. E.Z. provided the model data and calculated the correlation decay length information. All authors contributed to discussion and interpretation of the results. F.C.L., P.J.K. and D.F. wrote the paper with input from the other co-authors.

Corresponding author

Correspondence to Fredrik Charpentier Ljungqvist.

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The authors declare no competing financial interests.

Additional information

Data and code is digitally archived at the NOAA Paleoclimatology/World Data Center for Paleoclimatology (https://www.ncdc.noaa.gov/paleo/study/19725).

Extended data figures and tables

Extended Data Figure 1 Estimated correlation decay length values.

a, The spatial decorrelation function ρ for centennial mean precipitation estimated from the output of the climate model ECHO-G35 over the period 1000–1990, following the procedure described in the Methods for the estimation of the centennial correlation decay length for hydroclimate variability. Distance is the correlation decay length from one point in kilometres. The different colours represent the latitudinal bands. b, An example of the estimated spatial autocorrelation function for centennial mean values of precipitation at latitudes 81.25° N, 80.00° N and 78.75° N, respectively, with the decorrelation length for latitude 80° N indicated in red. c, The simplified CDL function of hydroclimate variability at centennial timescales, derived from panel a, is used throughout the study to calculate the maximum search distances as a function of latitude.

Source data

Extended Data Figure 2 The fraction of land area, expressed as decadal means for 1900–1999, exceeding a given wetness or dryness threshold in the gridded reconstruction, model simulations, and instrumental precipitation data.

a, Weighted gridded proxy reconstruction derived from the subset containing only hydroclimate records resolved decadally or better. b, The same as a but for median-model anomaly values of annual precipitation. c, The same as a and b but for the Global Historical Climatology Network 5° × 5° (GHCN5) instrumental annual precipitation data. All decadal average values are standardized over the 1910–1979 period, and model and instrumental values are extracted from grid cells covered by gridded reconstructed values. The red horizontal bars denote the 50% levels.

Source data

Extended Data Figure 3 Boxplots showing decadal anomaly values of instrumental data, our gridded reconstruction, drought atlas data, and model simulation of precipitation over the 1900s.

a, Comparison of decadal anomalies between our gridded Northern Hemisphere (NH) hydroclimate reconstruction, the gridded 5 × 5° GHCN5 instrumental annual precipitation anomalies, the six individual model simulations (see Table 1) of annual precipitation and their median. b, Comparison of decadal anomalies between the Monsoon Asia Drought Atlas (MADA)21 and the corresponding domain in our gridded Northern Hemisphere hydroclimate reconstruction, the GHCN5 instrumental annual precipitation data set, and in the six individual model simulations of annual precipitation and their median. c, Comparison of decadal anomalies between the North American Drought Atlas (NADA)20 and the corresponding domain in our gridded Northern Hemisphere hydroclimate reconstruction, the GHCN5 instrumental annual precipitation data set, and in the six individual model simulations of annual precipitation and their median. The oval circles represent the mean, the small blank horizontal bar represents the median, the length of the bars represents the quartile range, and the dark grey dots represent the two standard deviation intervals, whereas the light grey dots represent outliers.

Source data

Extended Data Figure 4 Correlations between gridded proxy and model hydroclimate anomalies, and gridded hydroclimate temperature proxy anomalies.

a, Correlations between 45 centennial, lagged 25 years, weighted gridded proxy hydroclimate anomalies and their corresponding median total annual precipitation anomalies from six CMIP5 models, listed in Table 1, over the past twelve centuries. b, The Z-transformed block bootstrap p-values of the correlations shown in panel a. c, Correlations between 45 centennial, lagged 25 years, weighted gridded proxy hydroclimate anomalies and weighted gridded proxy temperature anomalies. d, The Z-transformed block bootstrap p-values of the correlations shown in panel c. Areas shown in grey in b and d have insignificant correlations.

Source data

Extended Data Figure 5 Simulated median values of annual precipitation from six atmosphere–ocean coupled general circulation models.

a, Raw, centennial, model anomaly median values calculated and treated and plotted in the same way as the hydrological proxy data. Only values from the same grid cells that are covered by proxy records are extracted (Methods). Anomalies are shown relative to the centennial mean and standard deviation over the eleventh–nineteenth centuries. The colour scale in both panels is truncated at −2 and 2. b Gridded, weighted, values for the same data over land areas with at least three independent grid values within the estimated centennial correlation decay length for centennial-scale hydrological variability.

Source data

Extended Data Figure 6 Centennial temperature proxy anomalies updated from ref.15.

a, Gridded, weighted, centennial proxy anomalies values derived from the data listed in Supplementary Table 2 and shown in Fig. 1b. Anomalies are shown relative to the centennial mean and standard deviation over the eleventh–nineteenth centuries. The colour scale is truncated at −2 and 2 and areas with insufficient proxy coverage to compute a gridded weighted mean value are left white. b, Gridded, weighted, centennial anomalies for simulated median values of annual mean temperature from six atmosphere–ocean coupled general circulation models. Only values from the same grid cells that are covered by proxy records are extracted (Methods).

Source data

Extended Data Figure 7 Gradients of proxy-reconstructed and simulated Northern Hemisphere centennial hydroclimate anomalies along three meridional transects for the tenth, twentieth and seventeenth centuries.

The tenth and twentieth centuries were the warmest centuries of the past twelve and the seventeenth century was the coldest. a, Smoothed, surfaced, and contoured weighted average centennial proxy anomalies for the tenth century (top right). The trend of the smoothed surfaced anomaly values, with their regression line, is shown along the meridional transects, passing through the densest data clusters (red line, North America; blue line, Europe and Africa; and black line, Asia). b, c, The same as a but depicting centennial proxy anomalies of hydroclimate for the seventeenth and the twentieth centuries, respectively. df, The equivalent analysis for the same centennial periods using median-model simulated values, extracted from the same proxy locations, of centennial precipitation anomalies (see Methods).

Source data

Extended Data Figure 8 Distribution and density of hydroclimate proxy records.

a, Number of contributing hydrological proxy records included in each proxy-centred anisotropic weighted mean calculation where there are three or more neighbouring proxies found in the search radius. b, Raw, centennial, hydroclimate proxy anomaly values derived from the data listed in Supplementary Table 1 and shown in Fig. 1a. Anomalies are shown relative to the centennial mean and standard deviation over the eleventh–nineteenth centuries. The colour scale is truncated at −2 and 2 and areas with insufficient proxy coverage to compute a gridded weighted mean value are left white.

Source data

Extended Data Figure 9 Histograms of cross-correlations with kernel density estimate added.

a, Cross-correlations between gridded hydroclimate proxy data and temperature proxy (PT) data. b, Cross-correlations between gridded hydroclimate model data and temperature model data. c, Cross-correlations between gridded hydroclimate proxy (PH) data and hydroclimate model (MH) data. d, Cross-correlations between gridded temperature proxy data and temperature model (MT) data. e, The same as a but Fisher-transformed. f, The same as b but Fisher-transformed. g, The same as c but Fisher-transformed. h, The same as d but Fisher-transformed. The thin curves in each histogram represent the kernel density estimates.

Source data

Extended Data Table 1 Results from multiple sensitivity tests of our gridded weighted hydroclimate reconstruction

Supplementary information

Supplementary Information

This file contains Supplementary Tables 1-6 and Supplementary References. (PDF 1466 kb)

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Ljungqvist, F., Krusic, P., Sundqvist, H. et al. Northern Hemisphere hydroclimate variability over the past twelve centuries. Nature 532, 94–98 (2016). https://doi.org/10.1038/nature17418

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