| Description |
The flows of the Indus River are a vital resource for food security, ecosystem services, hydropower, and economy for millions of people living in China, India, Afghanistan, and Pakistan. Glaciers of the high altitude Karakoram Mountains are the largest drivers of discharge in the Upper Indus Basin, and combined with snowmelt constitute the majority of runoff. While mass balance for the region remains only slightly negative since the 1970s, the glaciers of the Karakoram exhibit substantial variability both in time and space. Complex climatology, coupled with the challenges of field study in this rugged range, illicit notable uncertainties in observation and prediction of cryospheric response to changes in climate, and merit study of these systems on varying spatial and temporal scales. Spaceborne radar sensors acquire high spatial resolution imagery regardless of cloud cover or time of day, and offer unique insights into surface characteristics. Here we utilize Sentinel-1 Synthetic Aperture Radar (SAR) imagery to track transient snow lines and accumulation area ratios of wet snow on glaciers of the Shigar Watershed in the Karakoram Mountains of Pakistan through multiple ablation seasons. We evaluate the topographic effects of layover, shadow, and extreme local incidence angle on SAR imagery for the region, and compare SAR to optically derived snow cover maps. We quantitatively explore diurnal differences in radar ratio values, and examine their spatial and temporal context through the melt seasons of 2015 and 2017. Lastly, we discuss potential changes in surface conditions that could lead to diurnal changes in radar signal. SAR indications of snowpack conditions could provide critical insights into surface energy balance processes in remote alpine watersheds that are useful for both glacier mass balance modeling and runoff forecasting. |
