Less extreme and earlier outbursts of ice-dammed lakes since 1900

Episodic failures of ice-dammed lakes have produced some of the largest floods in history, with disastrous consequences for communities in high mountains(1-7). Yet, estimating changes in the activity of ice-dam failures through time remains controversial because of inconsistent regional flood databases. Here, by collating 1,569 ice-dam failures in six major mountain regions, we systematically assess trends in peak discharge, volume, annual timing and source elevation between 1900 and 2021. We show that extreme peak flows and volumes (10 per cent highest) have declined by about an order of magnitude over this period in five of the six regions, whereas median flood discharges have fallen less or have remained unchanged. Ice-dam floods worldwide today originate at higher elevations and happen about six weeks earlier in the year than in 1900. Individual ice-dammed lakes with repeated outbursts show similar negative trends in magnitude and earlier occurrence, although with only moderate correlation to glacier thinning(8). We anticipate that ice dams will continue to fail in the near future, even as glaciers thin and recede. Yet widespread deglaciation, projected for nearly all regions by the end of the twenty-first century(9), may bring most outburst activity to a halt.

Automated summary

Episodic failures of ice-dammed lakes have caused catastrophic floods in high mountains. By analyzing 1,569 ice-dam failures in six major mountain regions, we find that extreme peak flows and volumes have significantly decreased since 1900, while median flood discharges have remained stable or slightly decreased. Ice-dam floods today occur at higher elevations and earlier in the year compared to 1900. Ice-dammed lakes with repeated outbursts also show a similar decline in magnitude and earlier occurrence, although with only moderate correlation to glacier thinning. Widespread deglaciation by the end of the twenty-first century may bring most outburst activity to a halt.