Glacier surface temperature warming in the Himalaya-Karakoram: Implications for glacier mass loss

Over the past two decades, glaciers in the Himalaya-Karakoram (HK) region have exhibited heterogeneous but accelerated mass loss. Factors driving this loss, such as atmospheric warming and snowfall variability, have been extensively studied by analyzing precipitation and air temperature data, often derived from meteorological reanalysis data. However, reanalysis data such as ERA5 exhibit significant biases and uncertainties, resulting in large spread in glacier mass balance estimates across studies. To address this, we propose to use thermal remote sensing data from the MODIS satellite, which provides glacier surface temperature (GST) at an 8-day temporal and 1 km spatial resolution.

This study leverages 24 years (2000–2024) of MODIS land surface temperature data to analyze GST characteristics, seasonality, and trends across HK subregions. Since temperature modulates glacier mass balance, remote-sensing-based GST is likely to be a superior dataset for mass balance modelling. We demonstrate this by obtaining a strong correlation (r: -0.47; p-value: 0.02) between GST and mass balance for ~6000 glaciers in the HK region. We also show that MODIS-derived GST outperforms ERA5 surface temperature when validated against in-situ surface temperature data measured on glaciers (R²: 0.88, RMSE: 3.57 °C vs. R²: 0.38, RMSE: 8.01 °C).

Our analysis of the spatiotemporal behaviour of GST reveals that during the ablation season, GST has been increasing at an average rate of +0.25 °C dec^-1across the HK region, with the Eastern Himalaya experiencing the highest warming (+0.44 °C dec^-1). Ablation months, August and September, exhibit more pronounced GST warming compared to other months. Comparisons between the decadal averages (2001-2010 vs. 2011-2020) indicate a marked increase in GST, on average +0.18 °C higher in the second decade across the HK subregions, with the Karakoram showing a threefold higher warming rate than others. Altitudinally, GST warming is strongest in mid-glacier areas (4300-5300 m), predominantly clean-ice zones, which warmed +0.30 °C more than debris-covered areas.

In the Eastern Himalaya, rising GST has significantly increased the annual positive GST area ratio (fraction of glacierised area with > 0 °C GST) by ~3% of total glacierised area, contributing to the region's steeper glacier mass loss than other subregions. Overall, the Eastern Himalaya stands out as a hotspot for GST warming, with significant increases annually, during the ablation season, and across altitudinal zones, making it highly vulnerable to persistent and accelerated glacier mass loss.

This study highlights the utility of satellite-derived GST for assessing glacier thermal states and their mass loss characteristics, offering valuable insights into glacier-surface-atmosphere interactions.