RECENT SPATIOTEMPORAL PATTERNS IN SEASONAL SNOWLINES FOR GLACIERS IN THE WESTERN CORDILLERA

Future climate change is expected to strongly impact streamflow seasonality and annual discharge in the Western Cordillera, in part due to changes in the absolute and relative magnitudes of snow and glacier melt to the local hydrologic system. The seasonal snowline and snow-covered area (SCA) are critical parameters for estimating when and where the snowpack completely melts. Changes in these parameters over time are important indicators of both glacier surface mass balance and freshwater discharge from snow and ice. Although the SCA and snowline can be mapped on global scales using satellite observations, the trade-off between spatial and temporal resolution of satellite imagery historically limited the accuracy and applications of remote seasonal snowline and SCA measurements. Additionally, despite the use of the end-of-melt-season snowline as a proxy for the glacier equilibrium line altitude (i.e., elevation of zero mass balance), well-established SCA classification methods have not been calibrated or thoroughly evaluated in glacierized environments. Here we employ a supervised classification approach to detect the seasonal snowline on glaciers using Landsat 8/9, Sentinel-2, and PlanetScope imagery. We apply the method to several glaciers spanning a range of latitudes in both maritime and continental climate regimes throughout the Western U.S. and Canada to analyze recent spatiotemporal trends in glacier seasonal snowlines since ~2016. In comparison to other years in the record, snowmelt in 2019 was especially early and rapid at many maritime glacier sites at all latitudes. Although observations at a single glacier do not directly correlate to regional trends, our findings have important implications for potential climatic and geometric controls on glacier surface mass balance and the timing of seasonal snow melt.