Distribution and relevance of aufeis (icing) in the Upper Indus Basin

Significant role of permafrost in regional hydrology of the Upper Indus Basin, India

Upper Indus Basin (UIB), being climatologically sensitive and socio-economically important, has emerged as a hotspot for eco-hydrological studies. Permafrost, one of the essential components of the regional hydrological cycle with a critical role in microclimate, is also an important water resource in the UIB. Despite being an important component of the cryospheric system, permafrost is least studied in the UIB. In present study, we used stable oxygen and hydrogen isotopic composition in supra-permafrost water (SPFW) and aufeis along with precipitation, snowpack, glacier and other groundwaters to assess their variability and estimate their contribution to regional hydrology. The sources are evolving isotopically, depending on physiographic and hydrometeorological factors, with each source attaining different (if not distinct) isotopic signatures. The isotopic signatures (with different ranges) of sources help in estimating the contribution from these sources. A significant altitude gradient of δ18O is observed in stream water, SPFW and other groundwaters. Isotopic composition in SPFW is differentially modulated by fractionation, resulting in isotopic variability from the source waters. The results suggest snowmelt and/or glacier melt as the source of SPFW. To stream flow, SPFW is the dominant contributor (43 ± 18 %) at higher elevations (> 4300 m a.m.s.l.) in July, followed by snowmelt (26 ± 10 %). In September, SPFW contribution decreases (14 ± 8 %), but the contribution from other groundwaters becomes dominant (39 ± 11 %) to stream flow. The results indicate the significant role of seasonal thawing and freezing of active layer on the contribution from SPFW. This study highlights the significant role of permafrost in the hydrological system of the basin. The study also emphasizes the need to understand the dynamics of permafrost, taliks of various types (e.g., supra-permafrost subaerial talik) and active layer under changing climate to define the subsequent implications to regional hydrology, eco-hydrological systems and micro-climate of permafrost regions.

Icings of the Kunlun Mountains on the Northern Margin of the Qinghai-Tibet Plateau, Western China: Origins, Hydrology and Distribution

Icing/Aufeis processes are a typical feature of permafrost hydrology in mountainous regions. Regional databases of Aufeis have been compiled since the 2010. In this study, we attempted to create an initial Aufeis database for the Qinghai-Tibet Plateau (QTP) to evaluate the patterns of the icing processes in the arid and high mountain regions at low latitudes. In this article, the icings/Aufeis in the Kunlun Mountains on the northern edge of the QTP were investigated. A total of 65 Landsat 8 Operational Land Imager images for 2017–2020 of the key sites were acquired. Icings occur at elevations of 2500–5400 m a. s. l. More than 1600 Aufeis were identified with a total ice-surface area of 2670 km2. About 88% of these areas are related to a gigantic Aufeis (tarin) field. Artesian aquifers related to the active faults play an important role in feeding the Aufeis in the Kunlun Mountains. About 120 Aufeis fed on glacier-melt have formed in the West Kunlun Mountains. Icing development was found to vary with the order of river channels and more than half of all of the identified Aufeis are located along first- and second-order river channels. The significance of Aufeis at the QTP related to as an indicator of climate change, and a volume of surface and ground waters conserved into Aufeis should take into consideration of river runoff estimation of the region.

Dynamic Lake Ice Movement on Lake Khovsgol, Mongolia, Revealed by Time Series Displacements from Pixel Offset with Sentinel-2 Optical Images

As one of the most sensitive indicators of global climate change, seasonal ice-covered lakes are attracting gaining attention worldwide. As a large seasonal ice-covered lake located in Northern Mongolia, Lake Khovsgol not only provides important freshwater resources for the local population but also serves as a means of water transportation in summer and an important land-based activity for residents in winter. In this study, we used the sub-pixel offset technique with multi-temporal Sentinel-2 optical images to estimate the time-series displacement of lake ice in Lake Khovsgol from 7 December 2020 to 17 June 2021. With the processing of 112 Sentinel-2 images, we obtained 27 pairs of displacement results at intervals of 5, 10, and 15 days. These lake ice movement results covered three stages from ice-on to ice-off. The first stage was the lake ice growth period, which lasted 26 days from 7 December 2020 to 3 January 2021. Ice formation started from the south and extended northward, with a displacement of up to 10 m in 5 days. The second stage was the active phase of the ice cover, which took place from 3 January 2021 to 18 April 2021. Maximum displacement values reached 12 m in the east and 11 m in the north among all observations. The value of the lake ice movement in the north–south direction (NS) was found to be larger than in the east–west direction (EW). The third stage was the melting period, which closed on 17 June 2021. In comparison to the freezing date of November in past years, our results demonstrate the ice-on date of Lake Khovsgol has been delayed to December, suggesting a possible reason that the seasonal ice-covered lake located at the middle latitude has been affected by global warming. In addition, the lake ice movement of our results can reveal the regional climate characteristic. This study is one of the few cases to reveal the distribution characteristics and changing trends of lake ice on the Mongolia Plateau, providing a rare reference for lake ice research in this region.