remote sensing Communication Current Status and Variation since 1964 of the Glaciers around the Ebi Lake Basin in the Warming Climate Lin Wang 1, Changbin Bai 1 and Jing Ming 2,* 1 State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China; [email protected] (L.W.); [email protected] (C.B.) 2 Beacon Science & Consulting, Malvern, SA 5061, Australia * Correspondence: [email protected] Abstract: This work analyzed the spatial and temporal variations of the glaciers in the Ebi Lake basin during the period 1964 to 2019, based on the 1st and 2nd Chinese Glacier Inventories (CGI) and remote sensing data; this is believed to be the first long-term comprehensive remote sensing investigation on the glacier change in this area, and it also diagnosed the response of the glaciers to the warming climate by analyzing digital elevation modeling and meteorology. The results show that there are 988 glaciers in total in the basin, with a total area of 560 km2 and average area of 0.57 km2 for a single glacier. The area and number of the glaciers oriented north and northeast are 205 km2 (327 glaciers) and 180 km2 (265 glaciers), respectively. The glaciers are categorized into eight classes as per their area, which are less than 0.1, 0.1–0.5, 0.5–1.0, 1.0–2.0, 2.0–5.0, 5.0–10.0, 10.0–20.0, and greater than 20.0 km2, respectively. The smaller glaciers between 0.1 km2 and 10.0 km2 account for 509 km2 or 91% in total area, and, in particular, the glaciers smaller than 0.5 km2 account for 74% in the total number. The glacial area is concentrated at 3500–4000 m in altitude (512 km2 or 91.4% in total). The number of glaciers in the basin decreased by 10.5% or 116, and their area decreased by 263.29 km2 (−4.79 km2 a−1) or 32% (−0.58% a−1) from 1964 to 2019; the glaciers with an area Citation: Wang, L.; Bai, C.; Ming, J. between 2.0 km2 and 5.0 km2 decreased by the largest, −82.60 km2 or −40.67% in the total area at Current Status and Variation since −1.50 km2 a−1 or −0.74% a−1), and the largest decrease in number (i.e., 126 glaciers) occurs between 1964 of the Glaciers around the Ebi 0.1 km2 and 0.5 km2. The total ice storage in the basin decreased by 97.84–153.22 km3 from 1964 to Lake Basin in the Warming Climate. 2019, equivalent to 88.06–137.90 km3 water (taking 0.9 g cm−3 as ice mass density). The temperature Remote Sens. 2021, 13, 497. https:// increase rate in the basin was +0.37 ◦C decade−1, while the precipitation was +13.61 mm decade−1 doi.org/10.3390/rs13030497 during the last fifty-five years. This analysis shows that the increase in precipitation in the basin was Academic Editor: Xander Wang not sufficient to compensate the mass loss of glaciers caused by the warming during the same period. Received: 29 December 2020 The increase in temperature was the dominant factor exceeding precipitation mass supply for ruling Accepted: 28 January 2021 the retreat of the glaciers in the entire basin. Published: 30 January 2021 Keywords: Ebi Lake basin; decelerated-melting glaciers; climate change; climate response Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. 1. Introduction The cryosphere consists of snow, ice, and permafrost on and below the Earth’s land and ocean surfaces, and it is one of the major components in the climate system [1]. The accelerated shrinkage of the cryosphere in the context of global warming and the subse- Copyright: © 2021 by the authors. quent impacts on the sustainability of the Anthroposphere have attracted unprecedented Licensee MDPI, Basel, Switzerland. attention and raised deep concern, because the High-Asian mountain glaciers are crucial for This article is an open access article buffering against drought [2] and protecting life from drought [3]. These mountain glaciers distributed under the terms and are an essential part of the global cryosphere and have shown generally varying degrees of conditions of the Creative Commons continuous retreat in recent decades [4–6]. As projected by the Intergovernmental Panel on Attribution (CC BY) license (https:// Climate Change (IPCC), even in the mild emission scenario (RCP4.5), the Asian glaciers creativecommons.org/licenses/by/ would disappear by ~50% by the end of the century [7]. 4.0/). Remote Sens. 2021, 13, 497. https://doi.org/10.3390/rs13030497 https://www.mdpi.com/journal/remotesensing Remote Sens. 2021, 13, x FOR PEER REVIEW 2 of 15 Remote Sens. 2021, 13, 497 2 of 14 China has the most developed mountain glaciers in low and middle latitudes [8], andChina these hasglaciers the most are a developed vital water mountain resource glaciers in arid innorthwest low and middleChina and latitudes High [Asia8], and [9]. theseAs global glaciers temperatures are a vital waterincrease, resource China’s in aridglacial northwest covers are China generally and High in negative Asia [9]. mass As globalbalance temperatures and showing increase, a retreating China’s and glacial thinning covers trend are generally [10–12]. inThe negative Xinjiang mass region balance is an andarid showing and semi-arid a retreating area andof China thinning rich trend in mountain [10–12]. The glaciers. Xinjiang The region Tianshan is an aridand andAltai semi-arid area of China rich in mountain glaciers. The Tianshan and Altai Mountains Mountains are two main mountains developing concentrated mountain glaciers. The are two main mountains developing concentrated mountain glaciers. The glaciers in the glaciers in the Tianshan Mountains had experienced rapid mass loss (averaged from Tianshan Mountains had experienced rapid mass loss (averaged from −24.6 mm w.e. a−1 −24.6 mm w.e. a−1 in 1957–1970 to −444.6 mm w.e. a−1 in 1971–2009) during the second half in 1957–1970 to −444.6 mm w.e. a−1 in 1971–2009) during the second half of the 20th of the 20th century [13]; while in Altai, over a quarter of mountain glaciers were projected century [13]; while in Altai, over a quarter of mountain glaciers were projected to shrink in to shrink in RCP4.5 by 2100 [14]. RCP4.5 by 2100 [14]. The Ebi Lake basin is located in the northwestern Xinjiang region, China (Figure 1). The Ebi Lake basin is located in the northwestern Xinjiang region, China (Figure1). The increasingly irrigated area and population in the basin over the last 60 years have led The increasingly irrigated area and population in the basin over the last 60 years have to increased water consumption in the basin, increasing tension between supply and led to increased water consumption in the basin, increasing tension between supply and demand, and the ecological degradation [15–17]. This lake had shrunk by 50% from 1955 demand, and the ecological degradation [15–17]. This lake had shrunk by 50% from 1955 to 2013, as reported by NASA in 2014 [18]. Another study stated that the water area of the to 2013, as reported by NASA in 2014 [18]. Another study stated that the water area ofEbi the Lake Ebi Lakeshowed showed a significantly a significantly decreasing decreasing trend, trend, although although thethe precipitation precipitation was was in- increasingcreasing from from 2001 2001 to to 2016 [19]. [19]. Therefore, itit isis essentialessential toto assessassess the the regional regional glaciers glaciers changechange in in a a timely timely manner manner to to monitor monitor glacier glacier water water resources resources and and assess assess their their impact impact on on thethe water water resource resource supply supply in in the the basin. basin. This This aspect’s aspect’s research research has has conceptual conceptual and and practical practi- significancescal significances for water for water security, security, especially especially for industrial for industrial and agricultural and agricultural production production and economicand economic development development in this in ecologically this ecologically vulnerable vulnerable area. area. Figure 1. Study area with the Ebi Lake basin (5Y74) and related river and lake basins, where Kuitun River, Sikeshu River, JingheFigure River, 1. Study Daheyanzi area with River, the Ebi Sayram Lake Lake,basin and(5Y74) Bortala and related River sub-basinsriver and lake are annotatedbasins, where with Kuitun their CGIRiver, codes Sikeshu of 5Y741, River, 5Y742,Jinghe 5Y743, River,5Y744, Daheyanzi 5Y746, River, and 5Y746,Sayram respectively. Lake, and Bortala River sub-basins are annotated with their CGI codes of 5Y741, 5Y742, 5Y743, 5Y744, 5Y746, and 5Y746, respectively. In recent years, numerous studies used the topographic maps and remote sensing data of theIn Tianshan recent Mountains,years, numerous regional studies watersheds, used the and topographic typical reference maps glaciers and remote and revealed sensing thatdata the of regionalthe Tianshan glaciers Mountains, show retreating regional and wa thinningtersheds, [20 and–26 typical]. So far, reference very few glaciers studies and on therevealed glacier that change the statusregional have glaciers been carriedshow retrea out inting the and Ebi thinning Lake Basin. [20–26]. For example, So far, very Wang few Remote Sens. 2021, 13, 497 3 of 14 et al. used remote sensing data to partially reveal that there were around 450 glaciers in the Ebi Lake Basin, Tianshan, undergoing significant mass loss glacier changes from 1964 to 2004 [27]; Zhang et al. estimated the change of the Haxilegen 51 glacier in the basin from 1964 to 2006 and its response to climate [28].