Rock glaciers represent hidden water stores in the Himalaya

Abstract

In High Mountain Asia (HMA), ongoing glacier retreat affects human and ecological systems through reduced water availability. Rock glaciers are climatically more resilient than glaciers and likely contain potentially valuable water volume equivalents (WVEQ). In HMA knowledge of rock glaciers is extremely sparse and here we present the first systematic assessment of rock glaciers for the Himalaya, which encompass ~25,000 landforms with an estimated areal coverage of 3,747 km². We estimate the WVEQ of Himalayan rock glaciers to be 51.80 ± 10.36 km³ (41-62 trillion litres). Their comparative importance vs glaciers (rock glacier: glacier WVEQ ratio) in the Himalaya was 1:24, ranging between 1:42 and 1:17 in the East and Central Himalaya, respectfully. We show that Himalayan rock glaciers constitute hydrologically valuable long-term water stores. In the context of ongoing glacier recession and mass loss, their relative hydrological value in mountain regions will likely increase and deserves greater study. Main In High Mountain Asia (HMA), which comprises the Tibetan Plateau and its surrounding mountain ranges (including the Himalaya, Karakoram, Tien Shan, and Pamir), the cryosphere forms natural water towers that are integral for ecosystem services provision, and for supplying multiple societal needs to ~800 million people living in the mountains and surrounding lowlands 1. However, considerable continued glacier mass loss is projected throughout the twenty-first century 2-4. Under high-end climate scenarios, warming that exceeds 2 °C global average during the twenty-first century (RCP8.5), relative to the pre-industrial period will result in projected HMA glacier volume loss of ~95% by 2100, relative to the present-day. Volume losses are driven by an average temperature change of +5.9 °C and +20.9% rise in average precipitation, the latter increasingly of rain (Fig. 1). Indeed, reductions in snow water equivalent have been reported for a number of catchments in HMA, particularly during spring and summer 5. For the RCP4.5 scenario, most basins fed by HMA glaciers are projected to reach peak water by ~2050; 2045 ± 17 years (Indus), 2044 ± 21 years (Ganges) and 2049 ± 18 years (Brahmaputra), for example 6 .

Modelling rock glacier velocity and ice content, Khumbu and Lhotse Valleys, Nepal

“…By using the minimum and maximum inference values, the estimated ratio ranges between 1:21 and 1:13. Our modelling-based results are lower than earlier estimates (1:9), yet reveal higher hydrological importance than across the Himalayas (1:24) (Jones et al, 2018b;Jones et al, 2021).…”

“…Recent work (Jones et al, 2021) was the first to show that around 25,000 rock glaciers exist in the Himalayas, covering 3747 km² and containing 51.80 ± 10.36 km³ of water volume equivalent. The comparative importance of rock glacier ice content versus that in glaciers in the region was 1:25, ranging from 1:42 to 1:17 in the Eastern and Central Himalaya and falling to 1:9 in Nepal.…”

Detecting Rock Glacier Displacement in the Central Himalayas Using Multi-Temporal InSAR

“…Rock glaciers are widely distributed in the central Himalayas [58]. Following the baseline concepts and practical guidelines of the IPA Action Group rock glacier inventories and kinematics (version 4.1), we visually identified rock glaciers by referring to highresolution satellite images and manually delineated the outline of each rock glacier.…”

“…To investigate in detail the large-scale deformations of rock glaciers in the central Himalayas, the MT-InSAR method was applied to interferometric wide swath mode (IW) Sentinel-1A data from both ascending and descending orbits. A total of 12 tracks of ascending and descending data overlapping the rock glacier distribution were processed for this paper (Figure 1, Rock glaciers are widely distributed in the central Himalayas [58]. Following the baseline concepts and practical guidelines of the IPA Action Group rock glacier inventories and kinematics (version 4.1), we visually identified rock glaciers by referring to highresolution satellite images and manually delineated the outline of each rock glacier.…”

Rock Glacier Characteristics Under Semiarid Climate Conditions in the Western Nyainqêntanglha Range, Tibetan Plateau

“…Due to their high elevation and remote location, rock glaciers are usually assessed with remote sensing techniques (Jones et al, 2021;Z. Ran & Liu, 2018;Reinosch et al, 2021;Schmid et al, 2015;Villarroel et al, 2018).…”