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  • Matters Arising
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Concerns about data linking delta land gain to human action

Nature volume 614, pages E20–E25 (2023)Cite this article

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Matters Arising to this article was published on 08 February 2023

The Original Article was published on 22 January 2020

arising from J. H. Nienhuis et al. Nature https://doi.org/10.1038/s41586-019-1905-9 (2020)

River deltas are diverse, economically and ecologically important ecosystems that are increasingly vulnerable to environmental change. A recent study reported that human impacts on the morphology of deltas at the global scale has led to a net gain in land area1. However, we suggest that an unconventional definition of deltas, miscellaneous coastal features unduly characterized as deltas and misidentified changes in delta area have led to inaccurate statistical analyses in the study1 and that a recently published correction2 does not address our concerns. We call for the rigorous verification and analysis of large environmental datasets.

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Fig. 1: Previous categorization of river mouths as deltas.
Fig. 2: Misidentified land change shows no correlation with change in sediment flux.

Data availability

We used the original data provided by the corresponding author of Nienhuis et al.1 and data1 uploaded on GitHub (https://github.com/jhnienhuis/GlobalDeltaChange).

Code availability

All of the MATLAB codes used for the data analysis and figure production have been uploaded to GitHub (https://github.com/FlorinZai/Global_Delta_Check). Interactive Google Earth Engine scripts are also provided as links in the GitHub repository. These can be used to compare our operator-derived buffers with the automatic buffers of Nienhuis et al.1.

References

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Author information

Authors and Affiliations

  1. Institut Terre Environnement Strasbourg, UMR 7063, CNRS, Strasbourg, France

    Florin Zăinescu

  2. GEODAR Research Center, Faculty of Geography, University of Bucharest/RYA, Bucharest, Romania

    Florin Zăinescu, Alfred Vespremeanu-Stroe & Florin Tătui

  3. Aix Marseille University, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France

    Edward Anthony

  4. Sfântu Gheorghe Marine and Fluvial Research Station, University of Bucharest, Sfântu Gheorghe, Romania

    Alfred Vespremeanu-Stroe

  5. i-Sea SAS, Merignac, France

    Manon Besset

Authors
  1. Florin Zăinescu
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  2. Edward Anthony
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  3. Alfred Vespremeanu-Stroe
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  4. Manon Besset
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  5. Florin Tătui
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Contributions

All authors developed and contributed to drafts of the text and figures. The concept for this article was designed by E.A. and F.Z.; F.Z., F.T. and M.B. contributed to data analysis and acquisition. All authors contributed to the elaboration of the concepts presented here.

Corresponding author

Correspondence to Florin Zăinescu.

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The authors declare no competing interests.

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Extended data figures and tables

Extended Data Fig. 1 Statistical relationships further invalidating claim of delta land area gain due to humans.

Corrected Fig. 3a of Nienhuis et al.1 (ai) is compared with the same sediment flux change ratio with different data corrections for the V1 dataset. R2 of 0 with p = 0.0004 is obtained with x-axis values between 0 and 2 (92%) of the data. When the whole dataset is considered, p becomes non-significant (p = 0.98). A correction for the Yellow delta land changes results in R2 of 0 or very close to 0, and a p-value that is not statistically significant for bins (aii, blue). Max100 land change (our data) replaced into V1 dataset shows R2 = 0 and p that is not significant. Continuous lines show regressions for all the ‘delta’ points; dashed lines show regressions for the 20 bin averages; axes are extended to show the full variability of bins. Most of the large deltas fall beyond the chart’s y axis. Comparison of the ratio \({Q}_{{\rm{river}}}^{{\rm{d}}}/{Q}_{{\rm{river}}}^{{\rm{p}}}\) with version 2 (V2) land changes (bi), and of the difference \({Q}_{{\rm{river}}}^{{\rm{d}}}-{Q}_{{\rm{river}}}^{{\rm{p}}}\) with V2 land changes of Nienhuis et al.1 (bii); comparison of version 1 (V1, original) and V2 datasets of Nienhuis et al.1 for Max100 deltas shows low agreement for all deltas (ci), and no agreement for 75 deltas within ± 1 km2 land change (cii); comparison of V2 dataset of Nienhuis et al.1 with Max100 land change obtained through our data check and our buffers shows good agreement for all deltas (di), and fair agreement for 75 deltas within ± 1 km2 land change (dii).

Extended Data Fig. 2 Exemplification of misidentified land changes.

Distribution of our 108 random samples and the 100 largest deltas (Max100) on the sediment discharge continuum of Nienhuis et al.1 (ai), and their global distribution (aii). Note biased error check of Nienhuis et al.1 limited to Madagascar Island (aii) (see further comment on the Madagascar choice in the Supplementary Discussion); comparisons of land changes of Nienhuis et al.1 with our 108 random samples (44 polygons, bi, bii- zoom on data), and with the Max100 deltas (ci, cii- zoom on data). Plots bii, cii show subsets of their respective datasets, all with R2 = 0. Examples of wrongly identified land changes by Nienhuis et al.1 obtained on a selection of large deltas as a result of misplaced buffers (d, j), human-induced land transformations wrongly reported as natural land changes (e, f, h), and misidentified deltas (k). Original buffers (light grey) of Nienhuis et al.1 are compared with our re-drawn data-check buffers (yellow) based on which only natural, and not human-transformed, delta coastal change should be calculated.

Extended Data Table 1 Analysis of 108 randomly selected ‘river mouths’ from data of Nienhuis et al.1 showing numerous discrepancies
Full size table

Supplementary information

Supplementary Information

This file contains the Supplementary Methods and references.

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Zăinescu, F., Anthony, E., Vespremeanu-Stroe, A. et al. Concerns about data linking delta land gain to human action. Nature 614, E20–E25 (2023). https://doi.org/10.1038/s41586-022-05624-x

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