Recent controversy regarding changes in Himalayan glaciers, triggered by an erroneous statement in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (IPCC, 2007), has highlighted major gaps in knowledge of the present and future behavior of Himalayan glaciers and in understanding of the underlying processes. The description in the IPCC’s report referred to poorly substantiated estimates of the rates of recession and dates of disappearance of Himalayan glaciers. Meanwhile, views on changes in Himalayan glaciers by many researchers, including Japanese, have differed (e.g., Asahi, 2001; Waragai, 2010). It is well known that the ‘IPCC statement on the melting of Himalayan glaciers’ was released on 20 January 2010 (IPCC, 2010), in which IPCC had to correct its previous statement.

In addition, glacier changes not only imply change in water availability but also altered risks due to glacial hazards, not the least of which are glacial lake outburst floods (GLOFs). GLOFs are recognized worldwide, and in fact are considered a major natural hazard in the Himalayas. GLOFs have been studied in the Nepal Himalaya at least since the 1980s (Fushimi et al., 1985; Ives, 1986; Vuichard & Zimmermann, 1987), and the Imja Glacier Lake, one of the most heavily studied glacial lakes in Nepal, was first systematically examined in 1988 (Hammond, 1988). Nevertheless, research and mitigation measures have been limited, even in Nepal, mainly due to the high altitudes involved and difficult accessibility.

Much literature on glacier changes, glacial lakes, GLOFs and resultant phenomena has been published in South Asia, especially in the Nepal Himalaya. Such studies have greatly advanced in the last decade. However, there still exist regional imbalances in terms of the amount of knowledge of these phenomena. This special issue carries state-of-the-knowledge studies led by Japanese scientists, focusing mostly on the state of glaciers in the Bhutan Himalaya, which has been poorly understood.

GLOFs are a great concern not only to researchers but also to local communities. Knowledge of GLOFs is delivered to the local residents mostly through mass media and rumors, often resulting in unnecessary threats. In this regard, conducting research alone with no follow-up may not be appreciated; mitigating actions and dialogues with local residents together with research activities are important components of a well balanced approach. One project in Bhutan by the Japan International Cooperation Agency (JICA) and Japan Science and Technology Agency (JST) is providing a good example of bridging the gap between research and mitigation/dialogues with local residents on GLOF issues. In addition to promoting natural sciences, the GLOF project in Bhutan involves training of local experts, technology transfer, and a proposal for an early warning system.

Ten years have passed since the UN’s International Year of Mountains (IYM), and we can find increasing necessity for projects combining research itself with feedback mechanisms to the local communities. We do hope that this special issue, a contribution to the IYM Plus 10 by the Japanese science community, will lead to further development and promotion of research and action projects in mountain areas worldwide.

Note: Spellings of place names adopted in this issue vary among the papers, because they differ among different maps and information sources.

Glacial Lake Outburst Floods (GLOFs) are a major hazard of concern to mountain communities in the Himalayas. In 2009 we started a three-year research project, in which we have conducted evaluation of GLOF risk using satellite data, in-situ surveys, and breach and flood simulations, and have produced a hazard map of possible floods. We have primarily focused on the Mangde-Chhu basin, for which the GLOF hazard level has been believed to be high but information regarding mitigation has been lacking. In this article, we describe the structure and strategy of the research project, and major results obtained to date.

Two debris-covered glaciers and two debris-free glaciers were surveyed regarding their surface lowering in the Lunana region, in the northern part of Bhutan. Regarding the debris-covered ones, the lowering rates were estimated to be 0-3 m a^-1 and approximately 5 m a^-1 on the ablation areas of the Thorthormi and Lugge Glaciers, respectively, in 2002-2004. Glacier flow was also measured for the two glaciers. The results showed contrastively that compressive flow is clear on the Thorthormi Glacier but not on the Lugge Glacier. The contrast in the surface lowering and flow is discussed herein to infer a positive feedback mechanism between glacier shrinkage and glacial lake growth.

On the other hand, the surface lowering rates evaluated on debris-free glaciers were 3-4 m a^-1 on the lower part of the Jichu Dramo Glacier in 2003-2010, and 1-3 m a^-1 on a small unnamed glacier southeast of the Jaze La (pass) in 1999-2010. The lowering rate on the Jichu Dramo Glacier may have accelerated from the previous estimate in 1998-2003. In addition, several pairs of repeated photos are provided to show glacier shrinkages and retreats.

In the recent several decades, glacial lakes have been expanding at the terminus of debris-covered glaciers associated with glacier shrinkage in the Himalayas. Accordingly, glacial lake outburst floods (GLOFs) have become serious natural disasters in the Himalayas. Bathymetrical surveys have been carried out at several glacial lakes, and the relationship between the lake area and water volume has been illustrated. At the initial stage, several small lakes are distributed near the glacier terminus, and then they coalesce and become one large lake, and finally, the large lake expands rapidly through calving of the glacial front. Surface inclination, surface velocity and surface lowering of glaciers are significant indicators of glacial lake expansion. Future prediction of topographical changes in debris-covered glaciers is important in forecasting the formation and expansion of glacial lakes.

This study aims to develop and validate a new glacial lake inventory in order to gain an understanding of existing conditions. This is being done using optical imageries acquired by the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) and the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) onboard the Advanced Land Observing Satellite (ALOS, nicknamed ‘Daichi’). Glacial lakes can cause outburst floods when natural dams break, and they represent a serious hazard to downstream regions. A major challenge associated with glacial lake outburst floods (GLOFs) is the inability to predict when they will occur or how much damage they will cause. In order to mitigate GLOF hazard risks, a new glacial lake inventory of the Bhutan Himalayas using ALOS imageries is currently being developed, combining PRISM and AVNIR-2 results in imaging with a fine spatial resolution of 2.5 m and multi-spectral precise geolocation. In addition, PRISM can derive precise digital terrain information, i.e., digital surface model (DSM) using its along-track stereo capabilities. We describe the methodology used in the development of the ALOS-based glacial lake inventory, including image processing procedures, glacial lake extraction, accuracy assessments of the generated PRISM DSM for the entire country of Bhutan, and validation of the inventory.

Three glacial lakes, Zanam B, Zanam C and Metatshota, upstream on the Mangde Chhu River, central Bhutan, were selected to be studied as potentially hazardous in the generation glacial lake outburst floods (GLOFs). Disaster risks were analyzed by numerical simulation of a glacial lake outburst using the NWS-BREACH model with the adjusted parameters for reproducing the event of the Lake Luggye outburst in 1994, considering the possible scenario of a moraine dam breach, followed by an analysis of consequent flood risk occurrence using the FLO-2D model, hazard mapping of the flood inundation and risk identification reflecting the vulnerability of communities and facilities in downstream areas.

The results showed that in the uppermost village along the Mangde Chhu River the peak discharge of a GLOF would arise three hours after the outburst under a possible scenario of a breach of Lake Metatshota, and the flood would affect some houses and farmland situated on the lower terrace plain. The calculated hydrograph shows the flood level sharply rising to the peak within tens of minutes so that residents could hardly escape from the flood if they had taken no precautions. Community based disaster management, including early warning and awareness raising, would therefore be effective for GLOF disaster risk mitigation.

The internal structure of moraine dams, especially the distribution of core ice and bedrock, is one of the key factors in assessing GLOF risk. In this study, we discuss the interpretation of the results of 2D electric sounding at three moraines in northern central Bhutan from the standpoint of not only their specific resistivity values, but also distribution patterns, in conjunction with field observations and previous studies. We found that:

1) Zones of specific resistivity exceeding 100,000 ohm-m could be regarded as massive dead ice, while zones of 10,000 - 50,000 ohm-m were assumed to be a mixture of fragmented ice and rock debris, where the higher the value was, the higher the ice content.

2) Resistivity values of rock debris were 5,000 - 10,000 ohm-m depending on the water content of matrix materials and degree of freezing.

3) Resistivity values of bedrock overlapped those of rock debris in the moraine. However, in the case of the study area, some distinctive patterns of lower resistivity, such as steep angle zones that were concordant with lithological features of the bedrock of the area, were used to identify bedrock.

Further studies employing electric sounding accompanied by other exploration methods are still necessary to improve the accuracy of the interpretation.

Maintaining proper preparedness for GLOF hazards and drawing attention to the task of mitigation are important goals, necessitating exploration of past cases of outbursts. The frequency of GLOF occurrences is still unknown, because major outbursts which cause significant damage downstream are rare and records have been kept on them for only the past several decades. We have to collect as much data on past outburst events as possible, including unpublished and previously unknown incidents. As is obvious in the traces of known GLOFs, an outburst event leaves typical topographical and sedimentological features, i.e., 1) V-shaped trenches, 2) huge debris fan depositions and 3) subsequent devastated river beds. Hence, these features can be used as proof of past outburst events. We describe the 2009 Tshojo flood as the most recent case of a GLOF in the Bhutan Himalayas. The flood, which was initiated by dam leakage and water splashing on the surface from en-/sub-glacial passage, was a potentially dangerous hazard. Attention to such outburst events from invisible sources will be required in the future.

As for evaluating the frequency of GLOF incidents, besides the six cases reported in previous studies, we revealed a total of 15 other outburst cases in the Bhutan Himalayas using field survey data; Corona KH-4A, Hexagon KH9-9, Landsat7/ETM+, and ALOS/PRISM satellite data; and images from Google Earth. These 21 cases were found on the Tibetan branch of the Kuri Chu, and the Chamkhar Chu, Pho Chu, Mo Chu and Soe Chu rivers. Lake outbursts at the foot of cliffs with hanging glaciers were the most frequent cases, accounting for ten of the GLOFs. Seventeen of the 21 cases occurred before the 1970s, while four cases were counted during the period from the 1970s to 2010. Hence, the current frequency of outburst occurrences does not seem to have increased. Further research is urged, covering minor outburst events, and the scope has to be broadened at least to the Sikkim and Nepal Himalayas.

Various erosion and sedimentation disasters have been induced by glacial lake outburst floods (GLOFs) occurring along various segments of rivers in the Nepal and Bhutan Himalayas. This paper discusses such phenomena from the point of view of GLOF hazard management. In a U-shaped valley formed by past glaciation, a GLOF occurs as a debris flow from breached moraines. GLOFs may cause the collapse of banks along hills and terraces of glacial and fluvioglacial origin by toe erosion, and the vegetation may not recover from the damage caused by the GLOFs for a long time and may act as a sediment source for the downstream river. The breaching of temporary dams by the sediment-loaded flow of a GLOF or during associated landslides could aggravate the secondary damage along narrow river courses in V-shaped valleys. In the Lesser and Greater Himalayas, a dense distribution of old deep-seated landslides and rock creep indicates the re-activation of landslides on slopes of rivers undercut by GLOFs. Woody debris may be produced from riparian forests in V-shaped valleys. In the case of gently sloping rivers in the basins of such valleys, bank erosion and the river blockage caused by woody debris from those valleys often pose serious risks, particularly, in terraces along the lower reaches of the rivers. Sand deposition in rivers and irrigation canals may adversely affect the downstream alluvial plain areas. In the case of topographical units such as river terraces that are prone to bank erosion, planning should be done for constructing bridges with appropriate dimensions. Geomorphological classification maps of the regions along rivers and DEM maps of the basins and alluvial plains are essential for planning for GLOF hazard management.

As part of the JICA/JST Glacial Lake Outburst Floods (GLOFs) project, we carried out a social survey in central Bhutan in 2010 to acquire fundamental information about local communities and means of communication in case of disasters.The surveyed areas were the Mangde Chhu basin, the target area of the project, and the neighboring Punatsang Chhu and Chamkar Chhu basins. The survey was conducted interview-style, using questionnaires to seek information from local governments, residential communities and schools. The findings of the survey were as follows.

Some communities in the Mangde Chhu basin, especially temporary camps for construction workers located on riverbanks, have a potential risk of human damage from GLOFs. In Zhemgang Dzongkhag, the ratio of residents with no communication tools is very high (42%), compared with the other areas (0%-13%). Generally, traditional communities in Bhutan are safe from floods, including GLOFs. However, temporary residents of local communities, such as people living in workers camps on riverbanks, are highly vulnerable to floods. Accordingly, a concrete disaster mitigation plan, including off-limits zones based on accurate hazard maps, is necessary. Also, early warning systems are very effective at mitigating damage from GLOFs. As for devices to alert the residents, other than sirens and loudspeakers, radio and mobile phones are most appropriate because of their high ownership ratios. In general, schools are well equipped with communication tools, and teachers have a good understanding of their local communities, thus, schools can act as a foothold for disaster mitigation measures providing regular disaster education to entire communities through their students.

We carried out multi-date morphological mappings to document the development of the glacial lake ‘Chamlang South Tsho’ in the eastern Nepal Himalaya over four decades. High-resolution Corona KH-4A and Advanced Land Observing Satellite (ALOS) PRISM stereo-data taken in 1964 and 2006 were processed in the Leica Photogrammetric Suite (LPS) to generate digital terrain models (DTMs). The DTMs produced topographic maps representing elevations and morphology of the glacier surface with a maximum error of +/- 10 m. A bathymetric map was also produced based on sonar sounding data obtained in November 2009. Extensive surface lowering was found to have occurred since 1964, as high as 156.9 m in the upper glacier area. The average lowering of the glacier for the entire 42-year period from 1964 to 2006 is 37.5 m, with the average surface-lowering rate calculated at 0.9 m/year. The average surface lowering for the 45 years from the glacier surface in 1964 to the lake bottom in 2009 was 99.5 m at a rate of 2.2 m/year. The minimum and maximum surface lowering during that period were 12 m and 153.8 m, respectively. The area surrounding the largest supraglacial pond in 1964 exhibited a low surface gradient, and there had already been a large degree of ice melting that favoured further lake expansion. The larger lowering rate at the lake area supports the previously presented idea that ice calving into the pond triggered the larger and faster up-glacial lake expansion.

Spatial and temporal variations in the suspended sediment concentration (SSC) of supraglacial lakes in debris-covered areas were investigated on the Lirung Glacier in the Langtang region of central Nepal from May to Octorber 1996. Twenty-eight lakes of various sizes were observed on the glacier. SSC varied widely among the lakes from 0 to 364 mg l^-1. Monthly observations showed that SSC of lakes also varied temporally, but there was no common trend in seasonality among the lakes. Measurement of the settling rate of suspended sediment in lake water indicated that SSC rapidly decreased from 37 mg l^-1 to 4 mg l^-1 within a day. Our results suggest that in lakes where SSC is high it is maintained mainly by a supply of high SSC meltwater to the lakes and that the low SSC of other lakes is due to little meltwater inflow to the lakes. Variations in SSC among lakes probably result from heterogeneous distribution of debris thickness and ice cliffs that affect the melting of glacial ice around the lakes. Seasonal changes in SSC are probably due to changing meteorological conditions and/or debris cover and ice cliffs around the lakes. The availability of lake turbidity would enable quicker and safer determination of the meltwater supply of lakes via remote-sensing techniques, and may be useful for elucidating the status of supraglacial lakes and glacier melting on debris-covered glaciers.

The worse air pollution due to haze from fires occurred in the Southeast Asia during the strongest 1997-1998 El Niño event in the last century. The dense haze came from forest and peat fires mainly occurred in Indonesia. Recent fires in Indonesia have become an annual phenomenon nevertheless rapid deforestation rate showed declined trend. In addition, Indonesia formally admitted very large amount of CO₂ emission mostly from fires and deforestation (about 3.01 billion tones after the United States). Indonesia is now requested to reduce air pollution due to haze and carbon emissions at the same time. For an execution of REDD+ (Reducing Emissions from Deforestation and Forest Degradation plus) in Indonesia, it is also essential to develop an effective firefighting strategy.

In this paper, recent hotspot data captured by NASA MODIS from 2002 to 2010 was analyzed to grasp the recent fire trend in the whole Indonesia. As Indonesia is not so small country, various grid sizes utilizing latitude and longitude angles from 1x1 to 0.01x0.01 degrees were used for various analysis purposes. Analysis results using one degree grids clearly showed the highest hotspot density areas in Indonesia located in Kalimantan and Sumatra Islands. Among them, One of the Mega Rice Project (MRP) regions (grid center: south latitude 3^o, east longitude 114^o) showed extremely high hotspot density, 0.188 hotspots/km²/year. Two regions in Riau and South Sumatra of Sumatra Island followed the MRP area and their hotspot densities were 0.111 and 0.106 hotspots/km²/year, respectively. Other high hotspot density regions were mostly found in deforested area on peat. Analysis results on seasonality of peat fire showed strong correlation with El Niño event. Finally, the authors are now proposing an effective fire forecast method based on recent fire trend in Indonesia.