What is the impact of climate change on stored snow and its significance in the Tibetan Plateau and the Himalayas?

The Himalayan range, which extends over~2400 km, constitutes the largest concentration of snow and ice after the two Polar Regions and is highly sensitive to the ongoing climate changes. The region feeds three major river basins namely: the Indus, the Ganga and the Brahmaputra Basins (Fig. 1) which in turn support a population of more than a billion people. Though there has been a large interest in studying the climatic variability over diferent parts of the cryospheric domain of the Himalaya, there still exists a wide gap in ground-based data as also the uncertainty in data on most aspects (Azam et al. 2021) such as the highly heterogeneous behaviour of glacial melting (Hugonnet et al. 2021). There is a negative balance in the eastern Himalaya, a relatively less negative mass balance in the western Himalaya and a in the Karakoram these are in balasnce. (Amir et al. 2018). Similarly, the estimates of snow cover and rainfall are also highly variable mainly because of an inadequate meteorological observatories in the highly inaccessible mountainous terrain. The decline in the glacier mass balance alters the local and regional hydrological cycle and is a major concern for the agrarian economy of India. Several Indian research institutes, governmental organizations, IITs, and Universities are engaged in conducting research and studying the dynamics of glaciers and their impact on the hydrological cycle natural hazards through remote sensing techniques and ground observations. A brief review of work related to the contemporary dynamics of glaciers in the Himalaya has been articulated in Kulkarni and Shirsat (2020), Sharma et al. (2021), Kulkarni et al. (2021b), Pant et al. (2018), Romshoo (2023), Arora (2018) and several others. A comprehensive data repository on the contemporary as well as paleao glaciers, from Sikkim in the East to Himachal in the West has been reconstructed using techniques ranging from geomorphological mapping, sedimentological analysis, geochemistry, absolute dating of soil and rocks using Infrared Stimulated Luminescence (IRSL), and 10Be Terrestrial Cosmogenic Nuclide (TCN) surface exposure dating (Sharma et al. 2021). Glacial mass balance studies and chronologies, landscape evolution Western Himalaya The topographic analysis of the various glacial valleys in the Western Himalaya (Fig. 1) such as the Sutlej and Bhaga basins indicates a general tendency of loss in smaller glaciers; losing a higher percentage of area as compared to the larger glaciers (Das et al. 2023a, b; Mandal and Sharma 2020). Analysis of a total of 306 glaciers (>0.2 km2 ) with an area of 360.3 ± 4.0 km2 , inventoried between 1971 and 2020, showed accelerated glacier shrinkage (∼8.2±1.5% or 0.16 ± 0.03% year−1) during this period which correlates well with the climatic variability. The signifcant winter temperature increase and year-round precipitation decrease in the Bhaga basin, since the 1990s, have probably augmented ice loss during the early twenty-frst century (Das et al. 2023a, b). Most of the glaciers in this basin have experienced critical thinning and lost huge ice mass in the range from − 6.07 m w.e. to − 9.06 m w.e. during 2008–2018 (Nagajothi et al. 2020). In-depth work in the transitional zone between the monsoon-dominated Pir-Panjal and westerly-dominated TransHimalaya Chandrabhaga basin (Das et al. 2023a); including the Miyar and Thirot watersheds in the Upper Chenab, has been carried out in the recent years (Deswal et al. 2023). The ice mass loss of Gepang Gath Glacier (GGGL) in Chandra basin, western Himalaya was assessed by Kumar et al. (2021a) using multi-year satellite dataset of Landsat series (TM, ETM+and OLI, 1989–2017), indicating~0.28 km3 of ice volume loss between 1989 and 2017. The glacier retreated~846 m with an average rate of 30 m a−1 and lost~0.73±0.05 km2 frontal area from 1989 to 2017. The studies over parts of western Himalaya covering the ranges in the upper Indus Basin (Romshoo 2023; Abdullah et al. 2020) using the TanDEM-X and SRTM-C Digital Elevation Models (DEMs) from 2000 to 2012 have shown that 12,243 numbers of glaciers of the region have thinned on an average of −0.35±0.33 m a−1 during the observation period. Higher thickness reduction was observed on the glaciers situated at lower altitudes (−1.40±0.53 m a−1) and with shallower slopes (−1.52±0.40 m a−1). The cumulative glacier mass loss of−70.32±66.69 giga tonnes (GT) was observed during the observation period, which, if continued, would signifcantly afect the sustainability of water resources in the basin. Rana et al. (2023) described the morphological and dynamic changes of Parkachik Glacier, Suru River valley, Ladakh Himalaya using satellite images of the period, 1971–2021 supported by feld campaigns between 2015 and 2021. The result reveal that overall, the glacier retreated by − 210.5 ± 80  m with an average rate of 4 ± 1 m a−1 between 1971 and 2021. In contrast, a feld study suggested that the glacier retreat increased to−123±72 m at an average rate of−20±12 m a−1 between 2015 and 2021. Under an integrated Himalayan Cryospheric Observation and Modelling (HiCOM) program, National Centre for Polar and Ocean Research (NCPOR) has been conducting glaciological studies on six benchmark glaciers of Chandra and adjoining basin in Western Himalaya to collecting ground data for estimation of glacial mass balance and energy budget of glaciers. These studies have revealed that the mean annual mass wastage of Chandra basin glaciers was −0.21 m w.e. before 2000 which increased signifcantly to−0.56 m w.e. after 2000 (Patel et al 2021). Chandra basin has lost 3.8 GT (0.62 m w.e a−1) of glacier mass with a mean thing of 5.5 m during the last 9 years (2013–2022). Annual mass loss of monitored glaciers in the Chandra basin varies from+0.71 m w.e. a−1 to −1.65 m w.e. a−1. A model-based study revealed that the Chandra basin glaciers have been losing mass with a mean annual mass balance of−0.59±0.12 m w.e. a−1 during 2013–2019 (Patel et al. 2021). Similarly, other adjoining basins Miyar and Parvati have also been continuously losing a huge mass (0.85 m w.e a−1). Studies related to energy balance in the Chandra basin (Oulkar et al. 2022; Pratap et al. 2019) have highlighted that inward fuxes account for most of the total heat fux over the ablation zone, resulting in strong summertime melting. The study revealed that the net radiation (RN) contributes~75% in total energy (FM) during the melt season while sensible heat (HS), latent heat (Hl ), and ground heat (HG) fuxes shared 15%, 8%, and 2%, respectively. Net short-wave radiation progressively increases during ablation and decreases during winter but net long-wave radiation works as a sink of energy throughout the year. Higher positive sensible and latent heat fux over the ablation zone during summer of the glacier surface enhances the ice ablation and contributes~88% of total ice melt. Geological Survey of India (2020) has been monitoring Neh Nar, Rulung (Jammu & Kashmir); Gara, Gor-Garang, Shaune Garang, Hamtah (Himachal Pradesh) on a long-term basis, for example, the mass balance studies of the Hamtah glacier that started in 2010 are still going on. Based on the geomorphological mapping, Infrared Stimulated Luminescence (IRSL), and 10Be Terrestrial Cosmogenic Nuclide (TCN) surface exposure dating techniques, various stages in the movement of glaciers in the Chandra basin have been dated. The oldest Chandra Glacial Stage is found to be contemporaneous to the late Marine Isotope Stage 6 (MIS 6; 186±30–113±10 ka) and also synchronous with some of the north-western Himalayan established glacial chronologies (Das et al. 2023a). Four local glacial stages in the Upper Chenab basin are: 1. the Chandra, 2. the Batal, 3. Dali, and 4. Mayar; each succeeding advance stood many degrees smaller than the previous episode. A similar corresponding trend exists for the adjoining Beas basin but each episode is many degrees smaller in magnitude. Results indicate that since the presumed Little Ice Age period extensions, glaciers in the region have experienced terminus retreat and area loss (Deswal et al. 2023).