Understanding glacier dynamics since the Little Ice Age in the sub-basins of Chandrabhaga Basin, Lahaul Himalaya, India

This study quantifies the changes in glaciers since the Little Ice Age (LIA) in the sub-basins of the Chandrabhaga River basin of Lahaul Himalaya, Himachal Pradesh, India. It further illustrates the extent of the Little Ice Age (LIA) glaciers and provides the ability to understand the impact of climate change on glaciers. We mapped 1,011 contemporary glaciers in 2023 using Landsat satellite images and compared them to the LIA glacier extents. The total glacier area retreated from 1855.60 km 2 during the LIA to 1368.13 km 2 in the present (2023). Since the LIA, 26.27% (487.47 km 2 ) of the glacier area has retreated. However, the rate of glacier retreat varies spatially among the sub-basins of the Chandrabhaga basin. As the glacier vacated almost 24.66 and 31.69% in the Chandra and Bhaga sub-basins of the upper Chandrabhaga, respectively, up to Tandi, whereas 26.87% in the lower Chandrabhaga basin between Tandi and Udaipur, and 20.93% in Miyar sub-basin, which confluences at Udaipur from the right flank down the valley. The total number of glaciers has increased from 574 during the LIA to 1,011 at present, which is a result of bifurcation of tributary glaciers from main trunk glaciers due to increased warming and reduced precipitation in the region. The trend of increased temperatures is reflected in the 10 stations (TerraClimate gridded data) of the region. The temperature minimum (Tmin) and temperature maximum (Tmax) increased by 0.03 °C/year and 0.01 °C/year, respectively, and with a total shift of 0.77 ± 0.24 °C between 1958 and 2024, whereas, the total annual precipitation of 67 years (1958–2024) suggests a reduction of ~1.80 mm/year, indicating conditions for the negative glacier budget reflected through retreat. The retreating trend is further reflected in the equilibrium line altitude (ELA). Based on the toe-to-headwall altitude ratio (THAR), ELA indicates an upward shift from 5,162 m during LIA to 5,277 m during 2023, with a rise of 116 ± 35 m (2.24%) since LIA.