Mapping Himalayan glacial lake outburst flood hazard through time and space

When glacial dams fail catastrophically, the ensuing glacial lake outburst floods (GLOFs) can cause devastating impacts to downstream environments and infrastructure. Large-impact GLOFs imprint distinct geomorphic features in the landscape that can remain diagnostic for hundreds of years, particularly for GLOFs sourced from moraine-dammed lakes. In this work, we used multi-temporal very-high-resolution-satellite imagery to systematically map the occurrence of impactful GLOFs from moraine-dammed lakes along the Himalayan arc between the Indus and the Salween rivers. Additionally, we binned mapped events by approximate date of occurrence to quantify changes in GLOF frequency through time. This new data set adds over 200 newly mapped GLOFs from ~200 lakes to the 108 events documented in published compilations. We find notable spatial heterogeneity in GLOF hazard along the Himalayan arc. Furthermore, we find that GLOF frequency from moraine-dammed lakes in the last 20 years is markedly lower than earlier time periods from 1970-2000 or from the end of the Little Ice Age to 1970. This decrease in GLOF frequency in recent time is despite continued growth of glacial lakes, likely increases in the frequency of mass movements that commonly trigger GLOFs from moraine-dammed lakes, and mapping bias that likely underestimates GLOF occurrence from earlier time periods.