Himalaya is experiencing unprecedented warming since recent past which is more than the global average and also more than the Indian sub continental landmass. The warming is even more pronounced at higher altitudes in Himalaya. This rising rate of warming at higher altitudes has been termed as Elevation Dependent Warming or EDW by the scientists working in the domain. The phenomenon of EDW is also observed in the Uttarakhand Himalaya using space based datasets. Uttarakhand is a Himalayan state of India with very diverse topography. A study carried out by the team of Scientists at Indian Institute of Remote Sensing (IIRS), ISRO (Pandey et. all, 2024) reported that about 25% of the total area of the Uttarakhand is located above an altitude of 3500 m asl as analyzed from digital elevation models and most of the part is covered with snow and glaciers ice throughout the years. Presence of snow and glacier ice at higher altitudes has a profound influence on the energy balance as they regulates the incoming and outgoing solar radiations. Snow and ice reflect backs most of the incoming solar radiation maintaining a colder atmosphere at higher altitudes. As the temperature at higher altitudes in Uttarakhand is rising fast, consequently the snow cover area is diminishing and subsequently the surface albedo is decreasing.
Figure: Bar plot graph compares the number of glacial lakes and the percentage change in the area (expansion) of the glacial lakes in the last two decades at every 500 m elevation zone of Uttarakhand Himalaya
In response to this elevated warming, the glaciers in Uttarakhand Himalaya are retreating and melting faster. The huge amount of melt water from accelerated melting of glaciers getting accumulated in the depression formed in the periphery of glaciers and causing formation and expansion of glacial lakes. A total of 209 glacial lakes (excluding highly dynamics ponds formed at glacier surface) with an area of 6.77 km2 were identified from satellite imageries of the year 2020 by the study done by a team at IIRS Dehradun. The glacial lakes were located between an elevation range of ~3040 and 5700 m asl, with numerous (more than 80%) lakes lying above 4600 m asl. Examining glacial lakes from 2000 to 2020 showed significant changes in the number and area of glacial lakes. The total number of glacial lakes in 2000 was 165, spanning 5.2 km2, which increased to 209 in 2021, spanning 6.77 km2, implying the formation of 44 new lakes. The glacial lake area increased by ~1.6 km2 (~31%). Altitudinal examination of lake development revealed that the number of glacial lakes rose dramatically above an altitude of 5200 m asl. In 2000, there were 67 glacial lakes above 5200 m asl, which increased to 102 in 2021, accounting for an increase in the lake area by ~0.38 km2 indicating the influence of EDW.
Figure
Glacial lake expansions in the central Himalaya, Uttarakhand, India, at various altitudes from 2000 (yellow polygon) to 2020 (black polygons). (a-b) Area change of a glacial lake located at ~4685 m asl in Niti valley, Alaknanda basin. (c-d) Area change of a glacial lake located at an elevation of ~4755 m asl. (e-f) Area change of Safed Lake (~4875 m asl) in the Goriganga basin. (g-h) Area change of a glacial lake located at ~ 5550 m asl in the Alkananda basin, upstream of Mana village, Badrinath area.
When glacier ice melts and becomes lakes or bare ground, the percentage of incoming solar energy/radiations that are absorbed and reflected varies. Because water absorbs between 80 and 90 percent of solar energy, it has the ability to heat its surroundings more than the barren surfaces can heat it. Greater and more concentrated insolation occurs at higher altitudes and lower latitudes. There is an increase in the area and number of lakes at higher elevations during the last two decades. Furthermore, above 5200 m asl, the number of lakes and area increased dramatically. The changes in snow-ice-lake distribution at higher altitudes have consequences for increased solar radiation absorption and heat storage, causing greater warming and a rise in temperature at higher elevations. As snow cover area and glacier ice decrease, a positive feedback loop produces a warming, snow and ice loss, reduced albedo, and increased solar radiation absorption as glacial lake water grows. Further, the growing meltwater bodies at higher altitudes has potential significant role in changing the solar radiation and surface energy balance and thus, local and regional climate and cryosphere and is a crucial part of snow-water-albedo-temperature feedback loop and hence EDW. Further, the most crucial implication of the high altitude temperature variability with increasing trend (EDW) is towards glacial hazards.
References:
Glacial Lakes of Uttarakhand, an Atlas (2020). https://antrikshgyan.iirs.gov.in/pdf/Glacial_Lake_Atlas_HR_Uttarakhand.pdf.
Pandey P., Ali S.N., Bhardwaj A., Banerjee B., Khan M.A.R., Fulkar P.G., (2024). Pattern and imprints of elevation-dependent warming on central Himalayan cryosphere as revealed by Earth Observation datasets. Results in Earth Sciences, Volume 2, 2024, 100021, ISSN 2211-7148, https://doi.org/10.1016/j.rines.2024.100021. (https://www.sciencedirect.com/science/article/pii/S2211714824000086)
Pandey P., Ali S.N., Champati Ray,P.K., (2021). Glacier-glacial lake interactions and glacial lake development in the central Himalaya, India (1994–2017). J. Earth Sci. 32 (6), 1563–1574.
Sabin T.P., Krishnan R., Vellore R., Priya P., Borgaonkar H.P., Singh B.B., Sagar A., (2020). Climate change over the Himalayas. In Assessment of climate change over the Indian region. Springer, Singapore, pp. 207–222.