Mapping seasonal glacier melt across the Hindu KushHimalaya with time series SAR

Abstract. Current observational data on Hindu Kush Himalayas (HKH) glaciers are sparse and characterizations of seasonal melt dynamics are limited. Time series synthetic aperture radar (SAR) imagery enables detection of reach-scale glacier melt characteristics across continents. We analyze C-band Sentinel-1 A/B SAR time series data, comprised of 32,741 Sentinel-1 A/B SAR images, determine the duration of seasonal glacier melting for 76,831 glaciers (65,108 km2), defined using optical observations, in the HKH across the calendar years 2017–2019. Signals of melt onset and duration are recorded at 90 m spatial resolution and 12-day temporal repeat across 96.62 % (62,907 km2) of the HKH cryosphere. Melt signals persist for more than 40 % of the year at elevations below 4,000 m a.s.l. and in excess of 15 % of each year at elevations exceeding 7,000 m a.s.l. Melt retrievals resemble characteristics of glacio-climatic subregions of the HKH: melt onsets sooner and occurs for a longer portion of each year in the Central and Eastern Himalaya compared to the Western Himalaya and Karakoram regions. Retrievals of seasonal melting span all elevation ranges of significant glacier area in the HKH region, extending greater than 1 km above the maximum elevation of an interpolated 0 oC summer isotherm. Furthermore, high elevation percolation zones are apparent from meltwater retention indicated by signals of delayed refreeze. Time series SAR datasets are suitable to support operational monitoring of glacier surface melt and the development and assessment of surface energy balance models of melt-driven ablation across the high-elevation temperate global cryosphere.