Pradeep K. Mool

Glaciers, glacial lakes and glacial lake outburst floods in the Mount Everest region, Nepal.

Abstract 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 ma–1. From 1976 to 2000, Lumding and Imja Glaciers retreated 42 and 34 ma–1, respectively, a rate that increased to 74 ma–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.

Glacial lake outburst flood risk assessment of Sun Koshi basin, Nepal

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 m3 s−1. 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

Glacial lake mapping with very high resolution satellite SAR data

197 million.

A comprehensive approach and methods for glacial lake outburst flood risk assessment, with examples from Nepal and the transboundary area

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 high-resolution 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.

Preliminary results of mass-balance observations of Yala Glacier and analysis of temperature and precipitation gradients in Langtang Valley, Nepal

Like other mountainous areas, Nepal is highly vulnerable to glacial lake outburst floods (GLOFs), and this vulnerability has increased due to climate change. Risk reduction strategies must be based on a comprehensive risk assessment. A comprehensive methodological approach for GLOF risk assessment is described and illustrated in case studies of the potential GLOF risk posed in Nepal by four glacial lakes, one located in China. People, property and public infrastructure (including hydropower plants, roads and bridges) are vulnerable, and there is a need to integrate GLOF risk reduction strategies into national policies and programmes.

Estimation of discharge from Langtang River basin, Rasuwa, Nepal, using a glacio-hydrological model

Abstract Monitoring the glacier mass balance of summer-accumulation-type Himalayan glaciers is critical to not only assess the impact of climate change on the volume of such glaciers but also predict the downstream water availability and the global sea-level change in future. To better understand the change in meteorological parameters related to glacier mass balance and runoff in a glacierized basin and to assess the highly heterogeneous glacier responses to climate change in the Nepal Himalaya and nearby ranges, the Cryosphere Monitoring Project (CMP) carries out meteorological observations in Langtang Valley and mass-balance measurements on Yala Glacier, a debris-free glacier in the same valley. A negative annual mass balance of –0.89m w.e. and the rising equilibrium-line altitude of Yala Glacier indicate a continuation of a secular trend toward more negative mass balances. Lower temperature lapse rate during the monsoon, the effect of convective precipitation associated with mesoscale thermal circulation in the local precipitation and the occurrence of distinct diurnal cycles of temperature and precipitation at different stations in the valley are other conclusions of this comprehensive scientific study initiated by CMP which aims to yield multi-year glaciological, hydrological and meteorological observations in the glacierized Langtang River basin.

Glacial Lake Outburst Flood Risk in the Poiqu/Bhote Koshi/Sun Koshi River Basin in the Central Himalayas

Abstract This paper provides the results of semi-distributed positive degree-day (PDD) modelling for a glacierized river basin in Nepal. The main objective is to estimate the present and future discharge from the glacierized Langtang River basin using a PDD model (PDDM). The PDDM is calibrated for the period 1993–98 and is validated for the period 1999–2006 with Nash–Sutcliffe values of 0.85 and 0.80, respectively. Furthermore, the projected precipitation and temperature data from 2010 to 2050 are obtained from the Bjerknes Centre for Climate Research, Norway, for the representative concentration pathway 4.5 (RCP4.5) scenario. The Weather Research and Forecasting regional climate model is used to downscale the data from the Norwegian Earth System Model general circulation model. Projected discharge shows no significant trend, but in the future during the pre-monsoon period, discharge will be high and the peak discharge will be in July whereas it is in August at present. The contribution of snow and ice melt from glaciers and snowmelt from rocks and vegetation will decrease in the future: in 2040–50 it will be just 50% of the total discharge. The PDDM is sensitive to monthly average temperature, as a 2°C temperature increase will increase the discharge by 31.9%. Changes in glacier area are less sensitive, as glacier area decreases of 25% and 50% result in a change in the total discharge of –5.7% and –11.4%, respectively.

Himalayan Glaciers (India, Bhutan, Nepal): Satellite Observations of Thinning and Retreat

The Himalayas have experienced several glacial lake outburst floods (GLOFs), and the risk of GLOFs is now increasing in the context of global warming. Poiqu watershed in the Tibet Autonomous Region, China, also known as the Bhote Koshi and Sun Koshi downstream in Nepal, has been identified as highly prone to GLOFs. This study explored the distribution of and changes in glacial lakes, past GLOFs and the resulting losses, risk from potential future GLOFs, and risk reduction initiatives within the watershed. A relationship was established between lake area and volume of lake water based on data from 33 lakes surveyed within the Hindu Kush Himalayan region, and the maximum possible discharge was estimated using this and other previously developed empirical equations. We recommend different strategies to reduce GLOF risk and highlight the need for a glacial lake monitoring and early-warning system. We also recommend strong regional cooperation, especially on issues related to transboundary rivers.

Remote sensing based glacial lake inventory in the Hindu Kush-Himalaya region

This chapter summarizes the current state of remote sensing of glaciers in the India, Nepal, and Bhutan regions of the Himalaya, and focuses on new methods for assessing glacier change. Glaciers in these Himalaya regions exhibit complex patterns of changes due to the unique and variable climatic, topographic, and glaciological parameters present in this region. The theoretical understanding of glaciers in the Himalaya is limited by lack of sufficient observations due to terrain breadth and complexity, severe weather conditions, logistic difficulties, and geopolitics. Mapping and assessing these glaciers with satellite imagery is also challenging due to inherent sensor limitations and information extraction issues. Thus, we still lack a complete understanding of the magnitude of feedbacks, and in some places even their sign, between climate changes and glacier response in this region. In this chapter we present the current status of glaciers in various climatic regimes of the Himalaya, ranging from the monsoon-influenced regions of the central-eastern Himalaya (Nepal, Garhwal, Sikkim, and Bhutan) through the monsoon transition zone of Himachal Pradesh (India), to the dry areas of Ladakh (western Himalaya). The case studies presented here illustrate the use of remote sensing and elevation data coupled with glaciermapping techniques for glacier area and elevation change detection and ice flow modeling in the context of the Himalaya.

Decadal glacial lake changes in the Koshi basin, central Himalaya, from 1977 to 2010, derived from Landsat satellite images

Glacial lake inventory is the main method to investigate the glacial lakes in remote area and provides required information for glacier risk management and climate change research. A glacial lake inventory based on Landsat TM/ETM+ images has been carried in Hindu-Kush Himalaya regions, and 20204 glacial lakes with total area of 1955.75 km2 are documented by this inventory. This paper introduced the method and material and discussed the merits and demerits of the method. Landsat based glacial lake inventory is effective method for large scale area, but more detail inventory with high resolution satellite images is necessary for glacier risk management and glacial lake change detection. The distribution characteristics is also analyzed by this paper, obvious regional difference was found by this inventory, the formation and distribution of glacial lake are controlled by terrain, glaciation and conditions. The selection of assessment method and criteria need to consider the regional feature of glacial lakes and their environment.