ABSTRACT
On July 8, 1998, the deadliest glacier lake outburst flood (GLOF) in Central Asia for at least the last 100 years occurred in the Shakhimardan catchment, Kyrgyzstan. Most of the >100 victims were, however, killed in the Uzbek enclave of Shakhimardan, i.e. in the downstream part of this transboundary catchment. No warnings were issued between the two countries. In addition, due to political tensions, access to the site was impossible and a detailed assessment of the disaster could not be realized until now. Using remote sensing, we show that the lake at the origin of the "Shakhimardan event" appeared in the 1960s and drained periodically, without, however, causing damage to downstream areas before it eventually disappeared in the late 1980s. Based on post-event videos, we conclude that the GLOF-producing depression was again filled with a lake, estimated at 20 ± 1.2 × 103 m2 in area, before the disaster. The lake burst was likely driven by the rapidly rising air temperatures and the melting of snow/ice in late June and early July. The GLOF first travelled as a debris flow for 17 km, then continued as a debris flood in the increasingly flatter channel for another 20 km. Interestingly, the mean weighted channel angle in the areas of erosion was extremely low at 6.7°. The flood continued further downstream for ~100 km from its source. Today, 32 lakes (total area ~300 × 103 m2 in 2018) exist in the catchment, with several of the larger lakes (>5 × 103 m2) showing signs of instability. We therefore call for a systematic monitoring of environments like the Shakhimardan catchment, as well as for the installation of early warning systems at critical sites, with exchange of data between the Kyrgyz and Uzbek disaster risk management units, so as to mitigate existing and evolving GLOF risks.
ABSTRACT
Climate change has been shown to increase the number of mountain lakes across various mountain ranges in the World. In Central Asia, and in particular on the territory of Uzbekistan, a detailed assessment of glacier lakes and their evolution over time is, however lacking. For this reason we created the first detailed inventory of mountain lakes of Uzbekistan based on recent (2002-2014) satellite observations using WorldView-2, SPOT5, and IKONOS imagery with a spatial resolution from 2 to 10m. This record was complemented with data from field studies of the last 50years. The previous data were mostly in the form of inventories of lakes, available in Soviet archives, and primarily included localized in-situ data. The inventory of mountain lakes presented here, by contrast, includes an overview of all lakes of the territory of Uzbekistan. Lakes were considered if they were located at altitudes above 1500m and if lakes had an area exceeding 100m2. As in other mountain regions of the World, the ongoing increase of air temperatures has led to an increase in lake number and area. Moreover, the frequency and overall number of lake outburst events have been on the rise as well. Therefore, we also present the first outburst assessment with an updated version of well-known approaches considering local climate features and event histories. As a result, out of the 242 lakes identified on the territory of Uzbekistan, 15% are considered prone to outburst, 10% of these lakes have been assigned low outburst potential and the remainder of the lakes have an average level of outburst potential. We conclude that the distribution of lakes by elevation shows a significant influence on lake area and hazard potential. No significant differences, by contrast, exist between the distribution of lake area, outburst potential, and lake location with respect to glaciers by regions.
