Adapting Lake Ice Phenology Method for Small, Rapidly Changing Glacial Lakes of the Nepalese Himalayas

<jats:p>Lakes globally are losing seasonal ice cover under climate change, a phenomenon studied under lake ice phenology (LIP). While LIP changes carry serious implications for lake ecology, LIP remains uncharacterized for small, rapidly changing glacial lakes in the Nepalese Himalaya. We present the first focused LIP study for five of Nepal's glacial lakes (&amp;gt;1 km&amp;sup2;) over 2001&amp;ndash;2025, updating the current remote sensing-based single-band reflectance method to account for the dynamic morphological and optical properties of these lakes. MODIS daily red-band reflectance, averaged over the lake and smoothed using a Savitzky-Golay filter, was related to Landsat-derived reference ice fraction observations to construct phenological time series and distinguish freeze and melt events. One lake (Imja) was excluded from phenological analysis due to a failed model fit, though its morphological and spectral properties were still assessed. Among the glacial lake changes observed, three lakes showed a rapid (1.8&amp;ndash;2.8 times) increase in surface area, two showed increased geometric complexity, and all showed lake-specific differences in spectral properties but no systematic within-lake spectral change over time. The ice-freeze season occurred from late November to early April, with only Tsho Rolpa's break-up start showing a nearly significant advancing trend (&amp;minus;1.55 days/year, p=0.07). Modelling uncertainties were varied and substantial, and results showed close dependence on parameter choices. These uncertainties and data limitations point to the need for in-situ monitoring networks to build long-term, validated records of how these vulnerable lake systems respond to a changing climate.</jats:p>