70 years of lake evolution and glacial lake outburst floods in the Cordillera Blanca (Peru) and implications for the future

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Climate change, glacier retreat and glacial lake outburst floods (GLOFs) are intertwined. The Cordillera Blanca in Peru has one of the world's longest GLOF records and here we assess the evolution of glacial lakes in the region between 1948 and 2017 and investigate the links to documented GLOFs. We also model future lake evolution under two climate scenarios to provide an assessment of current and future GLOF triggering potential. Our analysis shows that the number of lakes as well as the total lake area has increased during the historical period. The formation of new lakes is, however, not uniform among different lake types with bedrock-dammed lakes exhibiting the largest increase in recent decades. We argue that moraine-dammed lakes have already formed at the majority of potential locations in the Cordillera Blanca and that the next generation of lakes which are expected to form in response to glacier retreat over topographically suitable areas will be predominantly bedrock-dammed. Based on a regional GLOF inventory, we show that the peak frequency of GLOFs occurred from the late 1930s to early 1950s. While GLOFs originating from moraine-dammed lakes dominated in this period, recent GLOFs have originated from bedrock-dammed lakes. At the same time, the majority of GLOFs originated from lakes in a proglacial phase (i.e. in contact with glacier), even though the share of proglacial lakes did not exceed 12% at any time step during the analysed period. While many moraine-dammed lakes evolved into the glacier-detached evolutionary phase, bedrock-dammed lakes became a major lake dam type among proglacial lakes. Over the remainder of the 21st century, a further increase in lake area of up to 10% is anticipated, with up to 50 new bedrock dammed lakes likely to develop as glaciers retreat. There is little difference in lake development and GLOF triggering potential under climate scenarios driven by RCP 2.6 and 8.5. Based on topographic disposition, recent and future lakes do not individually appear more or less susceptible to landslide impact than lakes that already developed earlier in the 20th century. Synthesizing these findings, we forecast that bedrock-dammed lakes will become the dominant source of GLOFs in the next decades. Because such dams are inherently more stable, we expect overall lower GLOF magnitudes compared to documented GLOFs from moraine-dammed lakes.