The Hindu Kush-Himalayan (HKH) region extends over 2,000 km from east to west across the Asian continent spanning several countries: Afghanistan, Bangladesh, Bhutan, China, India, Nepal, and Pakistan (Figure S.1). This region is the source of numerous large Asian river systems, including the Indus, Ganges, and Brahmaputra, which provide water for over a billion people. The surface water of these rivers and associated groundwater constitute a significant strategic resource for all of Asia. Many of the countries in this region are already experiencing physical water scarcity. Existing water stress and projections of population growth have led to concern over possibilities of negative impacts from changes in the availability of water supplies in the coming decades.
Scientific evidence indicates that glaciers in the HKH region are retreating at rates comparable to those in other parts of the world, and confirms that the rate has accelerated in the past century. In this region, conventional wisdom is that glacial meltwater is an important supplement to naturally occurring runoff from precipitation and snowmelt. The watersheds of the area each exhibit complex hydrology and the magnitude of the contribution of glacial meltwater to the total water supply in these rivers is not clear and the implications of accelerated rates of glacial retreat and the resulting increase in glacial wastage for downstream populations have not been precisely characterized. Important questions about regional water security need to be addressed in the context of incomplete science and unresolved uncertainties.
The eastern and western areas of the HKH region differ in climate, especially in timing and type of precipitation, and in glacier behavior and dynamics as well. The Sutlej Valley serves as a rough dividing line, with precipitation in the eastern end of the region dominated by monsoonal activity in summer while precipitation in the western end is dominated by the mid-latitude westerlies in winter. There is evidence of glacial retreat in the eastern and central Himalayas while glaciers in the western Himalayas appear to be more stable, and may even be advancing. The HKH region is geographically vast and complex both climatologically and hydrologically, and this complexity is dynamic and possibly changing. This large spatial variability makes it very difficult to generalize observations and findings over the entire region.
The HKH region’s climate is changing. Although generally temperatures are increasing and these increases are likely to accelerate in coming decades, spatial variability and gaps in observational data mean that it remains unclear what specific manifestations of climate change will be in specific places—including where and how quickly glaciers might retreat and what the cumulative impacts on the hydrological system of the region will be. Moreover, it is difficult to separate the effects of changes in glacial wastage from other factors. These factors include changes in the timing and amounts of monsoonal rain and seasonal snowmelt, snow and ice dynamics, the effects of aerosols and black carbon,1 and the role of tectonic activity in destabilizing glaciers. In addition, water-use changes resulting from changes in population numbers and densities, livelihoods and
1 Black carbon refers to particulate matter derived from the incomplete combustion of a hydrocarbon.
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Summary T he Hindu Kush-Himalayan (HKH) region cipitation, and in glacier behavior and dynamics as well. extends over 2,000 km from east to west across The Sutlej Valley serves as a rough dividing line, with the Asian continent spanning several coun- precipitation in the eastern end of the region dominated tries: Afghanistan, Bangladesh, Bhutan, China, India, by monsoonal activity in summer while precipitation Nepal, and Pakistan (Figure S.1). This region is the in the western end is dominated by the mid-latitude source of numerous large Asian river systems, including westerlies in winter. There is evidence of glacial retreat the Indus, Ganges, and Brahmaputra, which provide in the eastern and central Himalayas while glaciers in water for over a billion people. The surface water of the western Himalayas appear to be more stable, and these rivers and associated groundwater constitute a may even be advancing. The HKH region is geographi- significant strategic resource for all of Asia. Many of cally vast and complex both climatologically and hydro- the countries in this region are already experiencing logically, and this complexity is dynamic and possibly physical water scarcity. Existing water stress and pro- changing. This large spatial variability makes it very jections of population growth have led to concern over difficult to generalize observations and findings over possibilities of negative impacts from changes in the the entire region. availability of water supplies in the coming decades. The HKH region's climate is changing. Although Scientific evidence indicates that glaciers in the generally temperatures are increasing and these increases HKH region are retreating at rates comparable to those are likely to accelerate in coming decades, spatial vari- in other parts of the world, and confirms that the rate ability and gaps in observational data mean that it has accelerated in the past century. In this region, con- remains unclear what specific manifestations of climate ventional wisdom is that glacial meltwater is an impor- change will be in specific places--including where and tant supplement to naturally occurring runoff from how quickly glaciers might retreat and what the cumu- precipitation and snowmelt. The watersheds of the area lative impacts on the hydrological system of the region each exhibit complex hydrology and the magnitude of will be. Moreover, it is difficult to separate the effects the contribution of glacial meltwater to the total water of changes in glacial wastage from other factors. These supply in these rivers is not clear and the implications factors include changes in the timing and amounts of of accelerated rates of glacial retreat and the resulting monsoonal rain and seasonal snowmelt, snow and ice increase in glacial wastage for downstream populations dynamics, the effects of aerosols and black carbon,1 and have not been precisely characterized. Important ques- the role of tectonic activity in destabilizing glaciers. In tions about regional water security need to be addressed addition, water-use changes resulting from changes in the context of incomplete science and unresolved in population numbers and densities, livelihoods and uncertainties. The eastern and western areas of the HKH region 1 Black carbon refers to particulate matter derived from the differ in climate, especially in timing and type of pre- incomplete combustion of a hydrocarbon. 1
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2 HIMALAYAN GLACIERS: CLIMATE CHANGE, WATER RESOURCES, AND WATER SECURITY FIGURE S.1 The Hindu-Kush Himalayan region extends over 2,000 km across South Asia and includes all or parts of Afghanistan, Bangladesh, Bhutan, China, India, Nepal, and Pakistan. The region is the source of many of Asia's major rivers, including the Indus, Ganges, and Brahmaputra. consumption patterns, water management decisions there remains substantial scientific uncertainty, snow including groundwater pumping, agricultural water-use and glacial melt will likely continue to be important dynamics, and the extent of pollutants will affect water sources of water in the region and there will be several availability in the region. climatological, glaciological, and hydrological factors Despite these important uncertainties, not every- that control the rate, volume, and timing of snowmelt thing is uncertain or unknown. The National Research and icemelt. The means of adapting to change will Council Committee on Himalayan Glaciers, Hydrol- mostly be small in nature, and adaptive solutions will be ogy, Climate Change, and Implications for Water essential. Effective management institutions will also Security was charged with addressing questions about be critical and will need to operate flexibly. Monitor- four aspects of water security in the region. The ing systems will be critical to implementing effective Committee's overarching conclusions are that while adaptation solutions and improving water management
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SUMMARY 3 systems. The following are more specific and detailed Uncertainties in the role of groundwater in the conclusions that relate to the questions in the Commit- overall hydrology of the region are even greater than tee's charge (the full charge can be found in Box 1.1 of those of surface water. Evidence suggests that sizable the main text of the report). and extensive overdraft in the central Ganges Basin is likely to have an earlier and larger impact on water How sensitive are the Himalayan glaciers to supplies than foreseeable changes in glacial wastage. changes in temperature, precipitation, and the sur- For upstream populations, glacial lake outburst floods face energy budget? and landslide lake outburst floods are the dominant The climate of the Himalayas is not uniform and physical hazard risks. For downstream populations is strongly influenced by the South Asian monsoon in in the central and eastern Himalayas, floods from the east and the mid-latitude westerlies in the west. changes in monsoon dynamics are more likely to Evidence suggests that the eastern Himalayas and the be important, along with changes in the timing of Tibetan Plateau are warming, and this trend is more extreme events. pronounced at higher elevations; however, the long- term significance of this trend is not clear. Absorbing What management systems (including water aerosols such as desert dust and black carbon may supply, water demand, land use, and other institu- contribute to the rapid warming of the atmosphere, and tions and infrastructure) are in place to manage model results indicate this may in turn contribute to climate-induced changes in regional hydrology, and accelerated melting of snowpack and glacial retreat. how might they be strengthened? The rate of retreat and growth of individual gla- Water resources management and provision of ciers is highly dependent on glacier characteristics and clean water and sanitation are already a challenge in the location. In the eastern and central Himalayas, there is HKH region. The adequacy and effectiveness of exist- evidence of glacial retreat with rates accelerating over ing water management institutions is a reasonable, if the past century. Retreat rates are comparable to other coarse, indicator of how the region is likely to cope with areas of the world. Glaciers in the western Himalayas changes in water supply. Changes in seasonal stream- appear to be more stable overall, with evidence that flow could have significant impacts on the local popula- some may even be advancing. tions by altering water availability patterns and affecting water management decisions and policies for irrigation, What does current glaciological and climatologi- municipal, industrial, and environmental use. cal knowledge imply about potential changes in cli- Current efforts that focus on natural hazards and mate on downstream flows? What are the likely major disaster reduction in the region can offer useful les- impacts on water supplies and flood regimes? sons when considering and addressing the potential Surface water flow is highly seasonal and var- for impacts resulting from glacial retreat and changes ies across the region, as does the relative importance in snowmelt processes in the region. Water manage- of glacial meltwater. In most instances, the annual ment assessments have advanced over the past 5 to 10 contribution of snowmelt and rainfall to streamflow years, though their implementation in water policies exceeds that of glacial wastage. The contribution of and programs is less clear; to date, there is limited glacial wastage can be more important when the glacial penetration to lower levels of governance or support for wastage acts as a buffer against hydrological impacts local water managers who are most at risk. Changes to brought about by a changing climate. Overall, retreat- the hydrological system are inevitable and adaptation ing glaciers over the next several decades are unlikely is needed at all levels of governance and throughout to cause significant change in water availability at lower societies from rural household to city level. Adapta- elevations, which depend primarily on monsoon pre- tion approaches need to be flexible enough to change cipitation and snowmelt. However, for high-elevation with changing conditions, for example, smaller scale areas, current rates of glacial retreat, if they continue, and lower cost water management systems, because appear to be sufficient to alter the seasonal and tem- of uncertainty in impacts and the dynamic nature of poral streamflow in some basins. future changes.
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4 HIMALAYAN GLACIERS: CLIMATE CHANGE, WATER RESOURCES, AND WATER SECURITY What are some of the main vulnerabilities to systems; (3) to reduce and respond to this uncertainty adjusting to changes in water supply in these down- there is a need for improved monitoring of both the stream areas? What are the prospects for increased physical and social systems; and (4) in the face of this competition, or improved cooperation, between dif- uncertainty, the most compelling need is to improve ferent downstream water users? What are some of the water management and hazard mitigation systems. implications for national security in the region? Theme 1: There is significant variability in the climate, Rural and urban poor may be most at risk, in part hydrology, and glacier behavior as well as the demographics because the poor are least likely to be able to retrofit, and water-use patterns in the region. The retreat rates of move, or rebuild as needed when faced with risks. Himalayan glaciers vary over time and space, with the Social changes in the region have at least as much of rate of retreat being higher in the east than the west. an effect on water use as environmental factors do on There are confounding factors such as dust and black water supply, leading to stress. Among the most serious carbon that could affect glacial melt and in some cases challenges, even in the absence of climate change, are increase glacial wastage. Changes in the monsoon will the magnitude of conflicting demands for limited water probably be more important than changes in glacial resources, the lack of corresponding institutional capac- wastage at lower, downstream elevations. Rates of ity to cope with such conflicts, and the current political urbanization vary across the region, as does the por- disputes among regional actors that complicate reach- tion of the population with access to improved water ing any agreements on resource disputes. Although the and sanitation. history of international river disputes and agreement in Theme 2: Uncertainties exist and will continue to this region suggests that cooperation is a more likely exist in both the physical and social systems. The impact outcome than violent conflict, social conditions may of future climate change is uncertain but will probably have changed in ways that make historical patterns accelerate rates of glacial retreat. Accelerated glacial less informative about current and future challenges; retreat rates will have significant impacts in local, high- populations are larger, the number of state and nonstate mountain areas but may not be important downstream actors has increased dramatically, patterns of economic unless the seasonal contribution of glacial meltwater growth have changed, and the resource challenges are to rivers is high or dense populations are dependent more complex. Changes in the availability of water on historical flow rates. As the region's population resources may play an increasing role in political ten- becomes more urbanized and standards of living sions, especially if existing water management institu- change, water-use patterns will also change in ways tions do not evolve to take better account of the social, that will be difficult to predict. Existing demographic economic, and ecological complexities in the region. methods also do not allow for projections at a sufficient Agreements will likely reflect existing political relations spatial resolution to determine whether, for example, more than optimal management strategies. The most certain river basins and elevation zones will experience dangerous situation to monitor for is a combination higher rates of population growth than others and how of state fragility (encompassing, e.g., recent violent the demographic composition of those specific areas conflict, obstacles to economic development, and weak will change. In both the physical and social systems, management institutions) and high water stress. stationarity--the assumption that the systems will fluctuate within a known range of variability--will no A WAY FORWARD longer apply. In other words, the past is not a good basis for prediction, and past trends in the climate, hydrol- When considering the link between humans and ogy, glacier behavior, population, and water use of the the environment within the context of water security region will not be a viable guide for the future. in the HKH region, four themes emerge: (1) there is Theme 3: To reduce and respond to this uncertainty significant variability in the climate, hydrology, and there is a need for improved monitoring of both the physical glacier behavior as well as the demographics and water- and social systems. Monitoring will need to occur on a use patterns within the region; (2) uncertainties exist more extensive and consistent basis. Without enhanced and will continue to exist in both the physical and social monitoring, the information needed to respond to
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SUMMARY 5 changing environmental and social conditions will of lessons from these assessments in water policies and be unavailable. Monitoring and research will advance programs will be necessary. Options for adapting to cli- understanding of both the physical and social systems mate change and hydroclimatic hazards are discussed in in the region, and identify the various options available greater detail in the report. However, the people most to respond to change in the face of uncertainty. likely to be affected by changing water security in the Theme 4: In the face of this uncertainty, the most region are the rural and urban poor who have the least compelling need is to improve water management and capacity to adapt to changing environmental and social hazards mitigation systems. Existing patterns of water conditions and hazards. Management of groundwater use and water management need improvement. Some and demand-side management are among the areas progress has been made in improved assessments in the where improvements can be made. recent past. Going forward, improved implementation
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