Glacier Albedo Reduction And Drought Effects In The Extratropical Andes, 1986-2020

Surface albedo typically dominates the mass balance of mountain glaciers, though long-term trends and patterns of glacier albedo are seldom explored. We calculated broadband shortwave albedo for glaciers in the central Chilean Andes (33-34 degrees S) using end-of-summer Landsat scenes between 1986 and 2020. We found a high inter-annual variability of glacier-wide albedo that is largely a function of the glacier fractional snow-covered area and the total precipitation of the preceding hydrological year (up to 69% of the inter-annual variance explained). Under the 2010-2020 'Mega Drought' period, the mean albedo, regionally averaged ranging from similar to 0.25-0.5, decreased by -0.05 on average relative to 1986-2009, with the greatest reduction occurring 3500-5000 m a.s.l. In 2020, differences relative to 1986-2009 were -0.14 on average as a result of near-complete absence of late summer snow cover and the driest hydrological year since the Landsat observation period began (similar to 90% reduction of annual precipitation relative to the 1986-2009 period). We found statistically significant, negative trends in glacier ice albedo of up to -0.03 per decade, a trend that would have serious implications for the future water security of the region, because glacier ice melt acts to buffer streamflow shortages under severe drought conditions.