On periodic growth and shrinkage of glaciers in the Warwan sub-basin, western Himalaya, between 1990 and 2020

Knowledge about glacier extent, dynamics, and characteristics are important for climate change attribution and prediction. Understanding on long-term dynamics and glacier inventory is crucial, particularly for the melt-dominated and latitudinally-diverse western Himalayan glacier basins. In this study, a temporal inventory is prepared for Warwan-sub basin (WSB), utilizing satellite imageries since the 1993 (Landsat TM: 1993; ETM⁺: 2001, 2008; OLI: 2020) and elevation model (SRTM DEM: 2000). The base inventory was generated for the year 2001 and systematically adjusted to the glacier situations in 1993, 2008, and 2020. Results indicate that in the year 2001, WSB in the western Himalaya included 84 glaciers (> 0.02 km²) covering an area of 187.9 ± 5.8 km². The mapping (2001) further revealed a supraglacial debris cover of 15% of the glacierized area (28.2 ± 0.9 km²). Overall, the debris cover increased by 6% between 1993 and 2020. Temporal analyses clearly suggest a period of gain in the glacierized area (2001-2008) interspersed by the two phases of decline (1993-2001 and 2008-2020). Results specify a stronger decline in the glacierized area during 1993 to 2001 (197.03 ± 6.1 to 187.9 ± 5.8 km²) than between 2008 and 2020 (188.4 ± 5.9 to 182.8 ± 5.66 km²). Remarkably, the glacierized area increased from 187.9 ± 5.8 to 188.4 ± 5.8 km² during 2001 to 2008. In view of widespread recession of regional glaciers, the gain in the area between 2001 and 2008 represents a peculiar characteristic of WSB that needs further detailed investigation. Further analyses suggest that low-altitude, east-facing, debris-free, steep-sloped, and small glaciers experienced greater loss in the area than large, debris-covered, north-facing, gently sloped, and high-altitude glaciers. Overall, the study at the sub-basin scale reveals inherent glacier dynamics with periodic increase and decrease in the glacierized area and a notable influence of non-climatic factors in regulating spatial heterogeneity and the rate of glacier changes.