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Increased outburst flood hazard from Lake Palcacocha due to human-induced glacier retreat


A potential glacial lake outburst flood from Lake Palcacocha (Cordillera Blanca, Peru) threatens Huaraz, a city of 120,000 people. In 1941, an outburst flood destroyed one-third of the city and caused at least 1,800 fatalities. Since pre-industrial times, Lake Palcacocha has expanded due to the retreat of Palcaraju glacier. Here we used observations and numerical models to evaluate the anthropogenic contribution to the glacier’s retreat and glacial lake outburst flood hazard. We found that the magnitude of human-induced warming equals between 85 and 105% (5–95% confidence interval) of the observed 1 °C warming since 1880 in this region. We conclude that it is virtually certain (>99% probability) that the retreat of Palcaraju glacier to the present day cannot be explained by natural variability alone, and that the retreat by 1941 represented an early impact of anthropogenic greenhouse gas emissions. Our central estimate is that the overall retreat is entirely attributable to the observed temperature trend, and that the resulting change in the geometry of the lake and valley has substantially increased the outburst flood hazard.

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Fig. 1: In situ (1939, 1940 and 1970) and satellite (1987 onwards) images showing the evolution of Lake Palcacocha.
Fig. 2: Regional observed and attributable temperature anomalies, and impacts on decadal mean mass-balance profile.
Fig. 3: Mass-balance response to temperature change and modelled and observed retreat of Palcaraju glacier.
Fig. 4: Analysis of the signal-to-noise ratio for Palcaraju glacier.

Data availability

All climate data (observations and reanalysis) that support the findings of this study are publicly available from the KNMI Climate Explorer (, except the Mayor General FAP Armando Revoredo Iglesias Airport station data, which was downloaded from the Center for Climate and Resilience Research (University of Chile) Climate Explorer ( All CMIP5 model data used in this study are available in public repositories, for example, The model data used here are stored on the Natural Environment Research Council’s (NERC) designated data centre for the atmospheric sciences, BADC (British Atmospheric Data Centre). The GWI data are available from

Code availability

Code will be available upon request to the corresponding author.


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We thank M. Baker and F. Otto for valuable comments and conversations, and K. Haustein for providing GWI data. R.F.S.-S. acknowledges support from the School of Geography and the Environment, University of Oxford, the Oxford Sustainable Law Programme and the Natural Environment Research Council grant NE/S007474/1, R.F.S.-S. and G.H.R. from NSF PLR-1643299 and S.L. and M.R.A. from The Nature Conservancy-Oxford Martin School Climate Partnership. We gratefully acknowledge support from The Nature Conservancy-Oxford Martin School Climate Partnership and NSF CLD2019647 and the personal computing time given by the CPDN volunteers for the RCM data used to support our findings in this article. We thank the estate of H. Kinzl, whose pioneering observations are shown in Fig. 1, for permission.

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All the authors planned the analyses, which R.F.S.-S. and G.H.R. performed. All the authors contributed to the interpretation of the results and to writing the manuscript.

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Correspondence to R. F. Stuart-Smith.

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Supplementary Discussion, Figs. 1 and 2, and Tables 1–3.

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Stuart-Smith, R.F., Roe, G.H., Li, S. et al. Increased outburst flood hazard from Lake Palcacocha due to human-induced glacier retreat. Nat. Geosci. 14, 85–90 (2021).

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