Calibration/Validation (C/V) studies using sites in the oceans have a long history and protocols are well established. Over lakes, C/V allows addressing problems such as the performance of the various retracking algorithms and evaluating the accuracy of the geophysical corrections for continental waters. This is achievable when measurements of specific and numerous field campaigns and a ground permanent network of level gauges and weather stations are processed. C/V consists of installation of permanent sites (weather stations, limnigraphs, and GPS reference points) and the organization of regular field campaigns. The lake Issykkul serves as permanent site of C/V, for a multi-mission purpose. The objective of this paper is to calculate the altimeter biases of Jason-3 and Sentinel-3A, both belonging to an operational satellite system which is used for the long-term monitoring of lake level variations. We have also determined the accuracy of the altimeters of these two satellites, through a comparison analysis with in situ data. In 2016 and 2017, three campaigns have been organized over this lake in order to estimate the absolute bias of the nadir altimeter onboard the Jason-3 and Sentinel-3A. The fieldwork consisted of measuring water height using a GPS system, carried on a boat, along the track of the altimeter satellite across the lake. It was performed at the time of the pass of the altimeter. Absolute altimeter biases were calculated by averaging the water height differences along the pass of the satellite (GPS from the boat system versus altimetry). Jason-3 operates in a Low Resolution Mode (LRM), while the Sentinel-3A operates in Synthetic Aperture Radar (SAR) mode. In this study we found that the absolute biases measured for Jason-3 were −28 ± 40 mm with the Ocean retracker and 206 ± 30 mm with the Ice-1 retracker. The biases for Sentinel-3A were −14 ± 20 mm with the Samosa (Ocean like) retracker and 285 ± 20 mm with the OCOG (Ice-1-like) retracker. We have also evaluated the accuracy of these two altimeters over Lake Issykkul which reached to 3 cm, for both the instruments, using the Ocean retracker.

Water vulnerabilities in Central Asia are affected by a complex combination of climate-sensitive water sources, trans-boundary political tensions, infrastructure deficiencies and a lack of water management organization from community to federal levels. This study aims to clarify the drivers of water stress across the 440 km Naryn River basin, headwater stem to the Syr Darya and the disappearing North Aral Sea. We use a combination of human and physical geography approaches to understand the meltwater-controlled hydrology of the system (using hydrochemical mixing models) as well as the human-water experience (via community surveys). Surveys indicate that current water stress is primarily a function of water management and access issues resulting from the clunky transition from Soviet era large-scale agriculture to post-Soviet small-plot farming. Snow and ice meltwaters play a dominant role in the surface and ground water supplies to downstream communities across the study's 4220 m elevation gradient, so future increases to water stress due to changes in volume and timing of water supply is likely given frozen waters' high sensitivities to warming temperatures. The combined influence of social, political and climate-induced pressures on water supplies in the Naryn basin suggest the need for proactive planning and adaptation strategies, and warrant concern for similar melt-sourced Central Asian watersheds.

This paper considers the results of complex glaciological and hydro meteorological observations in the basin of Chon Kyzyl Suu river for the period of 2013-2017; the analysis of flow formation from the Kara Batkak glacier was carried out. The main and minor factors of ice and snow ablation of Kara Batkak glacier are shown. The analysis of the main climatic parameters (air temperature and precipitation), which are changing in concordance with global warming, has been carried out. In the last 70 years the area of the Kara Batkak glacier has decreased by 21.8%, showing a pronounced trend of diminishing the area of this glacier, which is a consequence of global warming. It is established that the trend of increasing ablation over the entire observation period on the Kara Batkak glacier is associated with an increase in air temperatures over the last few decades.There is a good synchronization of annual trends of rise in air temperature at the three meteo stations for the period from 1961 to 2015 with a maximum of 7.0 °C at Kara-Batkak. This suggests that the same trend happens in all the regions of Teskey Ala Too, which in recent years, increase the trend of daily melting of ice. The mass balance in these basins over 60 years is negative due to rise in temperature and add to river runoff due to degradation and the reduction in the area of its glaciation confirmed the water-ice balance of mountain-glacial basins of the "continental" type glaciers. The close connection between the changes in climatic parameters, state of glaciations and glacial runoff in these river basin were established in this study.

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