Trends, Breaks, and Biases in the Frequency of Reported Glacier Lake Outburst Floods

Summary

This global analysis of 1,997 dated glacier-related floods reveals that the reported rise in glacier lake outburst floods cannot be readily attributed to atmospheric warming alone, as GLOF reports and glacier field surveys have decelerated whilst temperatures have accelerated over the past five decades. The authors identify a marked break in GLOF reporting trends after the 1970s and document substantial geographic and temporal biases, estimating that 40–80% of GLOFs may have gone undetected in the early–mid 20th century. The study underscores the need to account for reporting biases when attributing GLOF frequency changes to climate forcing.

Regional applicability

This is a global analysis with no specific focus on United Kingdom conditions or mountain ranges. However, the methodological insight regarding reporting biases and the decoupling between temperature trends and reported GLOF frequencies is relevant to any assessment of climate-driven hazard frequency trends worldwide, including in temperate or alpine regions with historical glacier lakes and limited early observation records.

Key measures

Frequency of reported GLOFs; annual air temperatures; annual number of field-based glacier surveys; temporal and geographic patterns in GLOF reporting across six mountain ranges; projected proportion of unnoticed GLOFs in early–mid 20th century

Outcomes reported

The study analysed trends in reported glacier lake outburst floods (GLOFs) across six major mountain ranges from 1901–2017, examining whether increases reflect atmospheric warming or reporting bias. Key findings include a distinct break in GLOF reporting trends after the 1970s, decoupling between accelerating temperature rise and declining GLOF reports in recent decades, and substantial underreporting of GLOFs in the early–mid 20th century.

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