Recent climate changes have had a significant impact on the high-mountain glacial environment. Rapid melting of glaciers has resulted in the formation and expansion of moraine-dammed lakes, creating a potential danger from glacial lake outburst floods (GLOFs). Most lakes have formed during the second half of the 20th century. Glaciers in the Mount Everest (Sagamartha) region, Nepal, are retreating at an average rate of 10-59 m a -1 . From 1976 to 2000, Lumding and Imja Glaciers retreated 42 and 34 m a -1 , respectively, a rate that increased to 74 m a -1 for both glaciers from 2000 to 2007. During the past decade, Himalayan glaciers have generally been shrinking and retreating faster while moraine-dammed lakes have been proliferating. Although the number of lakes above 3500 m a.s.l. has decreased, the overall area of moraine-dammed lakes is increasing. Understanding the behaviour of glaciers and glacial lakes is a vital aspect of GLOF disaster management.

The ongoing retreat of glaciers in the Hindu Kush-Himalaya (HKH) is associated with climate change. While deglaciation can cause a suite of impacts, one of the most visible and tangible impacts is the formation of glacial lakes. Some of these lakes can burst out causing large flash floods with the potential to cause significant damage to property, lives and livelihoods. At the moment, knowledge of the current glacial lake outburst flood (GLOF) risk in the HKH is incomplete, and a proper risk assessment is often circumvented. There is a need for a comprehensive GLOF risk assessment in order to support proper planning of mitigation and adaptation strategies in this context. In this paper we present a methodological approach for the GLOF risk assessment. The major part of the risk assessment is GLOF simulation and downstream impact assessment. The methodology was applied to the Sun Koshi river basin, a trans-boundary river basin between Tibet (China) and Nepal. A glacial lake outburst hydrograph was simulated using a dambreak model. The outburst flood was routed along the river using a hydrodynamic model to estimate the potential impact areas. A field survey was conducted to assess the potential damage caused by the GLOF. The peak outburst flood could be in the order of 7900 m 3 s 71 . The analysis shows that about 950 ha of land and a large amount of infrastructure are exposed to the GLOF. The economic risk due to the direct impact of a GLOF is estimated to be about US$197 million.

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Abstract. Floods resulting from the outbursts of glacial lakes are among the most far-reaching disasters in high mountain regions. Glacial lakes are typically located in remote areas and space-borne remote sensing data are an important source of information about the occurrence and development of such lakes. Here we show that very high resolution satellite Synthetic Aperture Radar (SAR) data can be employed for reliably mapping glacial lakes. Results in the Alps, Pamir and Himalaya using TerraSAR-X and Radarsat-2 data are discussed in comparison to in-situ information, and highresolution satellite optical and radar imagery. The performance of the satellite SAR data is best during the snow-and ice-free season. In the broader perspective of hazard management, the detection of glacial lakes and the monitoring of their changes from very high-resolution satellite SAR intensity images contributes to the initial assessment of hazards related to glacial lakes, but a more integrated, multi-level approach needs also to include other relevant information such as glacier outlines and outline changes or the identification of unstable slopes above the lake and the surrounding area, information types to which SAR analysis techniques can also contribute.

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