Water Security 11 (2020) 100072 Available online 15 November 2020 2468-3124/© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). The state and future of the cryosphere in Central Asia Martina Barandun a, b, * , Joel Fiddes c , Martin Scherler a , Tamara Mathys a , Tomas Saks a , Dmitry Petrakov d , Martin Hoelzle a a Department of Geosciences, University of Fribourg, Fribourg, Switzerland b Laboratory of Environmental Chemistry, Paul Scherrer Institute, Villigen, Switzerland c WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland d Faculty of Geography, Lomonosov Moscow State University, Moscow, Russia ABSTRACT Snow, glaciers and permafrost translate fuctuations of atmospheric conditions and highlight current environmental changes. Monitoring of these changes is one of the major objectives of the international climate observation strategy developed by the Global Climate Observing System (GCOS). Under ongoing climate change, the implication of altering meltwater released by snow, ice and permafrost will become increasingly relevant for the fragile mountain and lowland environments of Central Asia. These changes will affect the livelihood, particularly for mountain communities but also for the highly populated regions downstream. A degrading cryosphere may cause drastic ecological changes and endanger water, food and health security leading to pronounced political instabilities and changing socio- hydrological interactions. For successful mitigation, the adaptation capacity has to be enforced by frst creating basic observational datasets on the state and changes of the cryosphere, and secondly, by providing well-calibrated models in connection with climate scenario output. This information is a pre-condition to reduce on mid- to long-term the vulnerability of the local population. So far, signifcant data gaps of in situ measurements in Central Asia, mainly from the mid-1990 s to around 2010 impeded sound interpretations of long-term trends in the cryosphere. However, the progress made on glacier observation and capacity building in recent years, promises a future perspective for monitoring including snow and permafrost. This paper summarizes the current knowledge on the state of three essential climate variables (ECV) of the Central Asian cryosphere: snow, glaciers and permafrost in a context of future water security. It highlights the challenges for cryosphere assessments in the region and discusses ongoing monitoring efforts, future directions and emerging approaches, which might address current shortcomings of today’s monitoring network. 1. Relevance of the cryosphere for water availability The changing cryosphere has become an icon for climate warming [1]. Changes of snow, glaciers and permafrost translate the fuctuations of atmospheric conditions and highlight current environmental changes [2]. During the past decades such changes have strongly affected the major Central Asian mountain ranges Tien Shan and Pamir [3]. These form the north-western margin of High Mountain Asia (HMA, Fig. 1) hosting 25,000 + glaciers. Maximum snow cover can exceed 80% of the mountainous terrain and up to 32% of the lowlands [4]. Permafrost contains highly variable amounts of ice depending on the substrate (e.g. rock glacier, bedrock, fne material, etc). A rock glacier can contain ice contents between 10 and 90 vol% whereas massive bedrock has in general very low ice contents. The different landforms of permafrost are found in the Central Asian highlands but have so far not been quantifed. Ice and snowmelt are principal water resources for the highly populated lowlands of Central Asia e.g. [5–7], and have a crucial role for mountain communities [8–10]. Especially where irrigation is a general practise, continuous socio-hydrological interactions establish [8]. Snow accumulation acts as a water reservoir mainly during winter months, controlling river runoff in spring and early summer. With increasing summer precipitation towards the East, summer snowfall is frequent [11,12]. Snow strongly infuences the temperature regime in the ground, and therewith permafrost distribution [13–15]. Furthermore, fresh snow increases the albedo and hence provokes a signifcant reduction of glacier melt [16–18]. Glaciers and permafrost release most of their melt water during July to September. During dry and hot pe- riods, glacier melt is a vital fresh water source [19,20]. So far, it is un- known how much permafrost melt contributes to the total river runoff. Changes in the cryosphere have implications on the occurrence of natural hazards [21]. Hazards associated with glacier or permafrost degradation are expected to become more frequent and stronger in magnitude with the ongoing climate warming [22–24]. Associated processes could reach densely populated areas, might be transboundary and cause numerous victims (i.e. [25–27]). Increasing rates of glacier lake expansion from 0.8% yr 1 [28] to>3% yr 1 were observed for both the Tien Shan and Pamir [24,29]. However, no evidence of an increase in Glacier Lake Outburst Floods since 1970-ies could be observed [30], * Corresponding author. Contents lists available at ScienceDirect Water Security journal homepage: www.sciencedirect.com/journal/water-security https://doi.org/10.1016/j.wasec.2020.100072 Received 20 December 2019; Received in revised form 31 August 2020; Accepted 10 September 2020